* For simple stand-alone Java applications, a typical way to write * a line of output data is: *
* System.out.println(data)
* * See the {@code println} methods in class {@code PrintStream}. * * @see java.io.PrintStream#println() * @see java.io.PrintStream#println(boolean) * @see java.io.PrintStream#println(char) * @see java.io.PrintStream#println(char[]) * @see java.io.PrintStream#println(double) * @see java.io.PrintStream#println(float) * @see java.io.PrintStream#println(int) * @see java.io.PrintStream#println(long) * @see java.io.PrintStream#println(java.lang.Object) * @see java.io.PrintStream#println(java.lang.String) */ public static final PrintStream out = null; /** * The "standard" error output stream. This stream is already * open and ready to accept output data. *
* Typically this stream corresponds to display output or another * output destination specified by the host environment or user. By * convention, this output stream is used to display error messages * or other information that should come to the immediate attention * of a user even if the principal output stream, the value of the * variable {@code out}, has been redirected to a file or other * destination that is typically not continuously monitored. */ public static final PrintStream err = null; // indicates if a security manager is possible private static final int NEVER = 1; private static final int MAYBE = 2; private static @Stable int allowSecurityManager; // current security manager private static volatile SecurityManager security; // read by VM // return true if a security manager is allowed private static boolean allowSecurityManager() { return (allowSecurityManager != NEVER); } /** * Reassigns the "standard" input stream. * * First, if there is a security manager, its {@code checkPermission} * method is called with a {@code RuntimePermission("setIO")} permission * to see if it's ok to reassign the "standard" input stream. * * @param in the new standard input stream. * * @throws SecurityException * if a security manager exists and its * {@code checkPermission} method doesn't allow * reassigning of the standard input stream. * * @see SecurityManager#checkPermission * @see java.lang.RuntimePermission * * @since 1.1 */ public static void setIn(InputStream in) { checkIO(); setIn0(in); } /** * Reassigns the "standard" output stream. * * First, if there is a security manager, its {@code checkPermission} * method is called with a {@code RuntimePermission("setIO")} permission * to see if it's ok to reassign the "standard" output stream. * * @param out the new standard output stream * * @throws SecurityException * if a security manager exists and its * {@code checkPermission} method doesn't allow * reassigning of the standard output stream. * * @see SecurityManager#checkPermission * @see java.lang.RuntimePermission * * @since 1.1 */ public static void setOut(PrintStream out) { checkIO(); setOut0(out); } /** * Reassigns the "standard" error output stream. * * First, if there is a security manager, its {@code checkPermission} * method is called with a {@code RuntimePermission("setIO")} permission * to see if it's ok to reassign the "standard" error output stream. * * @param err the new standard error output stream. * * @throws SecurityException * if a security manager exists and its * {@code checkPermission} method doesn't allow * reassigning of the standard error output stream. * * @see SecurityManager#checkPermission * @see java.lang.RuntimePermission * * @since 1.1 */ public static void setErr(PrintStream err) { checkIO(); setErr0(err); } private static volatile Console cons; /** * Returns the unique {@link java.io.Console Console} object associated * with the current Java virtual machine, if any. * * @return The system console, if any, otherwise {@code null}. * * @since 1.6 */ public static Console console() { Console c; if ((c = cons) == null) { synchronized (System.class) { if ((c = cons) == null) { cons = c = SharedSecrets.getJavaIOAccess().console(); } } } return c; } /** * Returns the channel inherited from the entity that created this * Java virtual machine. * * This method returns the channel obtained by invoking the * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel * inheritedChannel} method of the system-wide default * {@link java.nio.channels.spi.SelectorProvider} object. * *
In addition to the network-oriented channels described in * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel * inheritedChannel}, this method may return other kinds of * channels in the future. * * @return The inherited channel, if any, otherwise {@code null}. * * @throws IOException * If an I/O error occurs * * @throws SecurityException * If a security manager is present and it does not * permit access to the channel. * * @since 1.5 */ public static Channel inheritedChannel() throws IOException { return SelectorProvider.provider().inheritedChannel(); } private static void checkIO() { SecurityManager sm = getSecurityManager(); if (sm != null) { sm.checkPermission(new RuntimePermission("setIO")); } } private static native void setIn0(InputStream in); private static native void setOut0(PrintStream out); private static native void setErr0(PrintStream err); /** * Sets the system-wide security manager. * * If there is a security manager already installed, this method first * calls the security manager's {@code checkPermission} method * with a {@code RuntimePermission("setSecurityManager")} * permission to ensure it's ok to replace the existing * security manager. * This may result in throwing a {@code SecurityException}. * *
Otherwise, the argument is established as the current * security manager. If the argument is {@code null} and no * security manager has been established, then no action is taken and * the method simply returns. * * @implNote In the JDK implementation, if the Java virtual machine is * started with the system property {@code java.security.manager} set to * the special token "{@code disallow}" then the {@code setSecurityManager} * method cannot be used to set a security manager. * * @param sm the security manager or {@code null} * @throws SecurityException * if the security manager has already been set and its {@code * checkPermission} method doesn't allow it to be replaced * @throws UnsupportedOperationException * if {@code sm} is non-null and a security manager is not allowed * to be set dynamically * @see #getSecurityManager * @see SecurityManager#checkPermission * @see java.lang.RuntimePermission */ public static void setSecurityManager(SecurityManager sm) { if (allowSecurityManager()) { if (security == null) { // ensure image reader is initialized Object.class.getResource("java/lang/ANY"); } if (sm != null) { try { // pre-populates the SecurityManager.packageAccess cache // to avoid recursive permission checking issues with custom // SecurityManager implementations sm.checkPackageAccess("java.lang"); } catch (Exception e) { // no-op } } setSecurityManager0(sm); } else { // security manager not allowed if (sm != null) { throw new UnsupportedOperationException( "Runtime configured to disallow security manager"); } } } private static synchronized void setSecurityManager0(final SecurityManager s) { SecurityManager sm = getSecurityManager(); if (sm != null) { // ask the currently installed security manager if we // can replace it. sm.checkPermission(new RuntimePermission("setSecurityManager")); } if ((s != null) && (s.getClass().getClassLoader() != null)) { // New security manager class is not on bootstrap classpath. // Force policy to get initialized before we install the new // security manager, in order to prevent infinite loops when // trying to initialize the policy (which usually involves // accessing some security and/or system properties, which in turn // calls the installed security manager's checkPermission method // which will loop infinitely if there is a non-system class // (in this case: the new security manager class) on the stack). AccessController.doPrivileged(new PrivilegedAction<>() { public Object run() { s.getClass().getProtectionDomain().implies (SecurityConstants.ALL_PERMISSION); return null; } }); } security = s; } /** * Gets the system-wide security manager. * * @return if a security manager has already been established for the * current application, then that security manager is returned; * otherwise, {@code null} is returned. * @see #setSecurityManager */ public static SecurityManager getSecurityManager() { if (allowSecurityManager()) { return security; } else { return null; } } /** * Returns the current time in milliseconds. Note that * while the unit of time of the return value is a millisecond, * the granularity of the value depends on the underlying * operating system and may be larger. For example, many * operating systems measure time in units of tens of * milliseconds. * *
See the description of the class {@code Date} for * a discussion of slight discrepancies that may arise between * "computer time" and coordinated universal time (UTC). * * @return the difference, measured in milliseconds, between * the current time and midnight, January 1, 1970 UTC. * @see java.util.Date */ @HotSpotIntrinsicCandidate public static native long currentTimeMillis(); /** * Returns the current value of the running Java Virtual Machine's * high-resolution time source, in nanoseconds. * * This method can only be used to measure elapsed time and is * not related to any other notion of system or wall-clock time. * The value returned represents nanoseconds since some fixed but * arbitrary origin time (perhaps in the future, so values * may be negative). The same origin is used by all invocations of * this method in an instance of a Java virtual machine; other * virtual machine instances are likely to use a different origin. * *
This method provides nanosecond precision, but not necessarily * nanosecond resolution (that is, how frequently the value changes) * - no guarantees are made except that the resolution is at least as * good as that of {@link #currentTimeMillis()}. * *
Differences in successive calls that span greater than * approximately 292 years (263 nanoseconds) will not * correctly compute elapsed time due to numerical overflow. * *
The values returned by this method become meaningful only when * the difference between two such values, obtained within the same * instance of a Java virtual machine, is computed. * *
For example, to measure how long some code takes to execute: *
{@code
* long startTime = System.nanoTime();
* // ... the code being measured ...
* long elapsedNanos = System.nanoTime() - startTime;}
*
* To compare elapsed time against a timeout, use
{@code
* if (System.nanoTime() - startTime >= timeoutNanos) ...}
* instead of {@code
* if (System.nanoTime() >= startTime + timeoutNanos) ...}
* because of the possibility of numerical overflow.
*
* @return the current value of the running Java Virtual Machine's
* high-resolution time source, in nanoseconds
* @since 1.5
*/
@HotSpotIntrinsicCandidate
public static native long nanoTime();
/**
* Copies an array from the specified source array, beginning at the
* specified position, to the specified position of the destination array.
* A subsequence of array components are copied from the source
* array referenced by {@code src} to the destination array
* referenced by {@code dest}. The number of components copied is
* equal to the {@code length} argument. The components at
* positions {@code srcPos} through
* {@code srcPos+length-1} in the source array are copied into
* positions {@code destPos} through
* {@code destPos+length-1}, respectively, of the destination
* array.
* * If the {@code src} and {@code dest} arguments refer to the * same array object, then the copying is performed as if the * components at positions {@code srcPos} through * {@code srcPos+length-1} were first copied to a temporary * array with {@code length} components and then the contents of * the temporary array were copied into positions * {@code destPos} through {@code destPos+length-1} of the * destination array. *
* If {@code dest} is {@code null}, then a * {@code NullPointerException} is thrown. *
* If {@code src} is {@code null}, then a * {@code NullPointerException} is thrown and the destination * array is not modified. *
* Otherwise, if any of the following is true, an * {@code ArrayStoreException} is thrown and the destination is * not modified: *
* Otherwise, if any of the following is true, an * {@code IndexOutOfBoundsException} is * thrown and the destination is not modified: *
* Otherwise, if any actual component of the source array from * position {@code srcPos} through * {@code srcPos+length-1} cannot be converted to the component * type of the destination array by assignment conversion, an * {@code ArrayStoreException} is thrown. In this case, let * k be the smallest nonnegative integer less than * length such that {@code src[srcPos+}k{@code ]} * cannot be converted to the component type of the destination * array; when the exception is thrown, source array components from * positions {@code srcPos} through * {@code srcPos+}k{@code -1} * will already have been copied to destination array positions * {@code destPos} through * {@code destPos+}k{@code -1} and no other * positions of the destination array will have been modified. * (Because of the restrictions already itemized, this * paragraph effectively applies only to the situation where both * arrays have component types that are reference types.) * * @param src the source array. * @param srcPos starting position in the source array. * @param dest the destination array. * @param destPos starting position in the destination data. * @param length the number of array elements to be copied. * @throws IndexOutOfBoundsException if copying would cause * access of data outside array bounds. * @throws ArrayStoreException if an element in the {@code src} * array could not be stored into the {@code dest} array * because of a type mismatch. * @throws NullPointerException if either {@code src} or * {@code dest} is {@code null}. */ @HotSpotIntrinsicCandidate public static native void arraycopy(Object src, int srcPos, Object dest, int destPos, int length); /** * Returns the same hash code for the given object as * would be returned by the default method hashCode(), * whether or not the given object's class overrides * hashCode(). * The hash code for the null reference is zero. * * @param x object for which the hashCode is to be calculated * @return the hashCode * @since 1.1 * @see Object#hashCode * @see java.util.Objects#hashCode(Object) */ @HotSpotIntrinsicCandidate public static native int identityHashCode(Object x); /** * System properties. The following properties are guaranteed to be defined: *
* The current set of system properties for use by the * {@link #getProperty(String)} method is returned as a * {@code Properties} object. If there is no current set of * system properties, a set of system properties is first created and * initialized. This set of system properties always includes values * for the following keys: *
| Key | *Description of Associated Value |
|---|---|
| {@systemProperty java.version} | *Java Runtime Environment version, which may be interpreted * as a {@link Runtime.Version} |
| {@systemProperty java.version.date} | *Java Runtime Environment version date, in ISO-8601 YYYY-MM-DD * format, which may be interpreted as a {@link * java.time.LocalDate} |
| {@systemProperty java.vendor} | *Java Runtime Environment vendor |
| {@systemProperty java.vendor.url} | *Java vendor URL |
| {@systemProperty java.vendor.version} | *Java vendor version |
| {@systemProperty java.home} | *Java installation directory |
| {@systemProperty java.vm.specification.version} | *Java Virtual Machine specification version, whose value is the * {@linkplain Runtime.Version#feature feature} element of the * {@linkplain Runtime#version() runtime version} |
| {@systemProperty java.vm.specification.vendor} | *Java Virtual Machine specification vendor |
| {@systemProperty java.vm.specification.name} | *Java Virtual Machine specification name |
| {@systemProperty java.vm.version} | *Java Virtual Machine implementation version which may be * interpreted as a {@link Runtime.Version} |
| {@systemProperty java.vm.vendor} | *Java Virtual Machine implementation vendor |
| {@systemProperty java.vm.name} | *Java Virtual Machine implementation name |
| {@systemProperty java.specification.version} | *Java Runtime Environment specification version, whose value is * the {@linkplain Runtime.Version#feature feature} element of the * {@linkplain Runtime#version() runtime version} |
| {@systemProperty java.specification.vendor} | *Java Runtime Environment specification vendor |
| {@systemProperty java.specification.name} | *Java Runtime Environment specification name |
| {@systemProperty java.class.version} | *Java class format version number |
| {@systemProperty java.class.path} | *Java class path (refer to * {@link ClassLoader#getSystemClassLoader()} for details) |
| {@systemProperty java.library.path} | *List of paths to search when loading libraries |
| {@systemProperty java.io.tmpdir} | *Default temp file path |
| {@systemProperty java.compiler} | *Name of JIT compiler to use |
| {@systemProperty os.name} | *Operating system name |
| {@systemProperty os.arch} | *Operating system architecture |
| {@systemProperty os.version} | *Operating system version |
| {@systemProperty file.separator} | *File separator ("/" on UNIX) |
| {@systemProperty path.separator} | *Path separator (":" on UNIX) |
| {@systemProperty line.separator} | *Line separator ("\n" on UNIX) |
| {@systemProperty user.name} | *User's account name |
| {@systemProperty user.home} | *User's home directory |
| {@systemProperty user.dir} | *User's current working directory |
* Multiple paths in a system property value are separated by the path * separator character of the platform. *
* Note that even if the security manager does not permit the * {@code getProperties} operation, it may choose to permit the * {@link #getProperty(String)} operation. * * @apiNote * Changing a standard system property may have unpredictable results * unless otherwise specified. * Property values may be cached during initialization or on first use. * Setting a standard property after initialization using {@link #getProperties()}, * {@link #setProperties(Properties)}, {@link #setProperty(String, String)}, or * {@link #clearProperty(String)} may not have the desired effect. * * @implNote * In addition to the standard system properties, the system * properties may include the following keys: *
| Key | *Description of Associated Value |
|---|---|
| {@systemProperty jdk.module.path} | *The application module path |
| {@systemProperty jdk.module.upgrade.path} | *The upgrade module path |
| {@systemProperty jdk.module.main} | *The module name of the initial/main module |
| {@systemProperty jdk.module.main.class} | *The main class name of the initial module |
On UNIX systems, it returns {@code "\n"}; on Microsoft * Windows systems it returns {@code "\r\n"}. * * @return the system-dependent line separator string * @since 1.7 */ public static String lineSeparator() { return lineSeparator; } private static String lineSeparator; /** * Sets the system properties to the {@code Properties} argument. * * First, if there is a security manager, its * {@code checkPropertiesAccess} method is called with no * arguments. This may result in a security exception. *
* The argument becomes the current set of system properties for use
* by the {@link #getProperty(String)} method. If the argument is
* {@code null}, then the current set of system properties is
* forgotten.
*
* @apiNote
* Changing a standard system property may have unpredictable results
* unless otherwise specified.
* See {@linkplain #getProperties getProperties} for details.
*
* @param props the new system properties.
* @throws SecurityException if a security manager exists and its
* {@code checkPropertiesAccess} method doesn't allow access
* to the system properties.
* @see #getProperties
* @see java.util.Properties
* @see java.lang.SecurityException
* @see java.lang.SecurityManager#checkPropertiesAccess()
*/
public static void setProperties(Properties props) {
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPropertiesAccess();
}
if (props == null) {
Map
* If there is no current set of system properties, a set of system
* properties is first created and initialized in the same manner as
* for the {@code getProperties} method.
*
* @apiNote
* Changing a standard system property may have unpredictable results
* unless otherwise specified.
* See {@linkplain #getProperties getProperties} for details.
*
* @param key the name of the system property.
* @return the string value of the system property,
* or {@code null} if there is no property with that key.
*
* @throws SecurityException if a security manager exists and its
* {@code checkPropertyAccess} method doesn't allow
* access to the specified system property.
* @throws NullPointerException if {@code key} is {@code null}.
* @throws IllegalArgumentException if {@code key} is empty.
* @see #setProperty
* @see java.lang.SecurityException
* @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
* @see java.lang.System#getProperties()
*/
public static String getProperty(String key) {
checkKey(key);
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPropertyAccess(key);
}
return props.getProperty(key);
}
/**
* Gets the system property indicated by the specified key.
*
* First, if there is a security manager, its
* {@code checkPropertyAccess} method is called with the
* {@code key} as its argument.
*
* If there is no current set of system properties, a set of system
* properties is first created and initialized in the same manner as
* for the {@code getProperties} method.
*
* @param key the name of the system property.
* @param def a default value.
* @return the string value of the system property,
* or the default value if there is no property with that key.
*
* @throws SecurityException if a security manager exists and its
* {@code checkPropertyAccess} method doesn't allow
* access to the specified system property.
* @throws NullPointerException if {@code key} is {@code null}.
* @throws IllegalArgumentException if {@code key} is empty.
* @see #setProperty
* @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
* @see java.lang.System#getProperties()
*/
public static String getProperty(String key, String def) {
checkKey(key);
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPropertyAccess(key);
}
return props.getProperty(key, def);
}
/**
* Sets the system property indicated by the specified key.
*
* First, if a security manager exists, its
* {@code SecurityManager.checkPermission} method
* is called with a {@code PropertyPermission(key, "write")}
* permission. This may result in a SecurityException being thrown.
* If no exception is thrown, the specified property is set to the given
* value.
*
* @apiNote
* Changing a standard system property may have unpredictable results
* unless otherwise specified.
* See {@linkplain #getProperties getProperties} for details.
*
* @param key the name of the system property.
* @param value the value of the system property.
* @return the previous value of the system property,
* or {@code null} if it did not have one.
*
* @throws SecurityException if a security manager exists and its
* {@code checkPermission} method doesn't allow
* setting of the specified property.
* @throws NullPointerException if {@code key} or
* {@code value} is {@code null}.
* @throws IllegalArgumentException if {@code key} is empty.
* @see #getProperty
* @see java.lang.System#getProperty(java.lang.String)
* @see java.lang.System#getProperty(java.lang.String, java.lang.String)
* @see java.util.PropertyPermission
* @see SecurityManager#checkPermission
* @since 1.2
*/
public static String setProperty(String key, String value) {
checkKey(key);
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPermission(new PropertyPermission(key,
SecurityConstants.PROPERTY_WRITE_ACTION));
}
return (String) props.setProperty(key, value);
}
/**
* Removes the system property indicated by the specified key.
*
* First, if a security manager exists, its
* {@code SecurityManager.checkPermission} method
* is called with a {@code PropertyPermission(key, "write")}
* permission. This may result in a SecurityException being thrown.
* If no exception is thrown, the specified property is removed.
*
* @apiNote
* Changing a standard system property may have unpredictable results
* unless otherwise specified.
* See {@linkplain #getProperties getProperties} method for details.
*
* @param key the name of the system property to be removed.
* @return the previous string value of the system property,
* or {@code null} if there was no property with that key.
*
* @throws SecurityException if a security manager exists and its
* {@code checkPropertyAccess} method doesn't allow
* access to the specified system property.
* @throws NullPointerException if {@code key} is {@code null}.
* @throws IllegalArgumentException if {@code key} is empty.
* @see #getProperty
* @see #setProperty
* @see java.util.Properties
* @see java.lang.SecurityException
* @see java.lang.SecurityManager#checkPropertiesAccess()
* @since 1.5
*/
public static String clearProperty(String key) {
checkKey(key);
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPermission(new PropertyPermission(key, "write"));
}
return (String) props.remove(key);
}
private static void checkKey(String key) {
if (key == null) {
throw new NullPointerException("key can't be null");
}
if (key.isEmpty()) {
throw new IllegalArgumentException("key can't be empty");
}
}
/**
* Gets the value of the specified environment variable. An
* environment variable is a system-dependent external named
* value.
*
* If a security manager exists, its
* {@link SecurityManager#checkPermission checkPermission}
* method is called with a
* {@code {@link RuntimePermission}("getenv."+name)}
* permission. This may result in a {@link SecurityException}
* being thrown. If no exception is thrown the value of the
* variable {@code name} is returned.
*
* System
* properties and environment variables are both
* conceptually mappings between names and values. Both
* mechanisms can be used to pass user-defined information to a
* Java process. Environment variables have a more global effect,
* because they are visible to all descendants of the process
* which defines them, not just the immediate Java subprocess.
* They can have subtly different semantics, such as case
* insensitivity, on different operating systems. For these
* reasons, environment variables are more likely to have
* unintended side effects. It is best to use system properties
* where possible. Environment variables should be used when a
* global effect is desired, or when an external system interface
* requires an environment variable (such as {@code PATH}).
*
* On UNIX systems the alphabetic case of {@code name} is
* typically significant, while on Microsoft Windows systems it is
* typically not. For example, the expression
* {@code System.getenv("FOO").equals(System.getenv("foo"))}
* is likely to be true on Microsoft Windows.
*
* @param name the name of the environment variable
* @return the string value of the variable, or {@code null}
* if the variable is not defined in the system environment
* @throws NullPointerException if {@code name} is {@code null}
* @throws SecurityException
* if a security manager exists and its
* {@link SecurityManager#checkPermission checkPermission}
* method doesn't allow access to the environment variable
* {@code name}
* @see #getenv()
* @see ProcessBuilder#environment()
*/
public static String getenv(String name) {
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPermission(new RuntimePermission("getenv."+name));
}
return ProcessEnvironment.getenv(name);
}
/**
* Returns an unmodifiable string map view of the current system environment.
* The environment is a system-dependent mapping from names to
* values which is passed from parent to child processes.
*
* If the system does not support environment variables, an
* empty map is returned.
*
* The returned map will never contain null keys or values.
* Attempting to query the presence of a null key or value will
* throw a {@link NullPointerException}. Attempting to query
* the presence of a key or value which is not of type
* {@link String} will throw a {@link ClassCastException}.
*
* The returned map and its collection views may not obey the
* general contract of the {@link Object#equals} and
* {@link Object#hashCode} methods.
*
* The returned map is typically case-sensitive on all platforms.
*
* If a security manager exists, its
* {@link SecurityManager#checkPermission checkPermission}
* method is called with a
* {@code {@link RuntimePermission}("getenv.*")} permission.
* This may result in a {@link SecurityException} being thrown.
*
* When passing information to a Java subprocess,
* system properties
* are generally preferred over environment variables.
*
* @return the environment as a map of variable names to values
* @throws SecurityException
* if a security manager exists and its
* {@link SecurityManager#checkPermission checkPermission}
* method doesn't allow access to the process environment
* @see #getenv(String)
* @see ProcessBuilder#environment()
* @since 1.5
*/
public static java.util.Map
* Severity values and Mapping to {@code java.util.logging.Level}.
*
* {@linkplain System.Logger.Level System logger levels} are mapped to
* {@linkplain java.util.logging.Level java.util.logging levels}
* of corresponding severity.
*
* An application can replace the logging backend
* even when the java.logging module is present, by simply providing
* and declaring an implementation of the {@link LoggerFinder} service.
*
* Default Implementation
*
* The system default {@code LoggerFinder} implementation uses
* {@code java.util.logging} as the backend framework when the
* {@code java.logging} module is present.
* It returns a {@linkplain System.Logger logger} instance
* that will route log messages to a {@link java.util.logging.Logger
* java.util.logging.Logger}. Otherwise, if {@code java.logging} is not
* present, the default implementation will return a simple logger
* instance that will route log messages of {@code INFO} level and above to
* the console ({@code System.err}).
*
* Logging Configuration
*
* {@linkplain Logger Logger} instances obtained from the
* {@code LoggerFinder} factory methods are not directly configurable by
* the application. Configuration is the responsibility of the underlying
* logging backend, and usually requires using APIs specific to that backend.
* For the default {@code LoggerFinder} implementation
* using {@code java.util.logging} as its backend, refer to
* {@link java.util.logging java.util.logging} for logging configuration.
* For the default {@code LoggerFinder} implementation returning simple loggers
* when the {@code java.logging} module is absent, the configuration
* is implementation dependent.
*
* Usually an application that uses a logging framework will log messages
* through a logger facade defined (or supported) by that framework.
* Applications that wish to use an external framework should log
* through the facade associated with that framework.
*
* A system class that needs to log messages will typically obtain
* a {@link System.Logger} instance to route messages to the logging
* framework selected by the application.
*
* Libraries and classes that only need loggers to produce log messages
* should not attempt to configure loggers by themselves, as that
* would make them dependent from a specific implementation of the
* {@code LoggerFinder} service.
*
* In addition, when a security manager is present, loggers provided to
* system classes should not be directly configurable through the logging
* backend without requiring permissions.
*
* Message Levels and Mapping to backend levels
*
* A logger finder is responsible for mapping from a {@code
* System.Logger.Level} to a level supported by the logging backend it uses.
*
* An implementation of {@code LoggerFinder} may override this method,
* for example, when the underlying logging backend provides its own
* mechanism for localizing log messages, then such a
* {@code LoggerFinder} would be free to return a logger
* that makes direct use of the mechanism provided by the backend.
*
* @param name the name of the logger.
* @param bundle a resource bundle; can be {@code null}.
* @param module the module for which the logger is being requested.
* @return an instance of {@link Logger Logger} which will use the
* provided resource bundle for message localization.
*
* @throws NullPointerException if {@code name} is {@code null} or
* {@code module} is {@code null}.
* @throws SecurityException if a security manager is present and its
* {@code checkPermission} method doesn't allow the
* {@code RuntimePermission("loggerFinder")}.
*/
public Logger getLocalizedLogger(String name, ResourceBundle bundle,
Module module) {
return new LocalizedLoggerWrapper<>(getLogger(name, module), bundle);
}
/**
* Returns the {@code LoggerFinder} instance. There is one
* single system-wide {@code LoggerFinder} instance in
* the Java Runtime. See the class specification of how the
* {@link LoggerFinder LoggerFinder} implementation is located and
* loaded.
* @return the {@link LoggerFinder LoggerFinder} instance.
* @throws SecurityException if a security manager is present and its
* {@code checkPermission} method doesn't allow the
* {@code RuntimePermission("loggerFinder")}.
*/
public static LoggerFinder getLoggerFinder() {
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
sm.checkPermission(LOGGERFINDER_PERMISSION);
}
return accessProvider();
}
private static volatile LoggerFinder service;
static LoggerFinder accessProvider() {
// We do not need to synchronize: LoggerFinderLoader will
// always return the same instance, so if we don't have it,
// just fetch it again.
if (service == null) {
PrivilegedAction
* This method calls the {@code exit} method in class
* {@code Runtime}. This method never returns normally.
*
* The call {@code System.exit(n)} is effectively equivalent to
* the call:
*
* The call {@code System.gc()} is effectively equivalent to the
* call:
*
* The call {@code System.runFinalization()} is effectively
* equivalent to the call:
*
* The call {@code System.load(name)} is effectively equivalent
* to the call:
*
* The call {@code System.loadLibrary(name)} is effectively
* equivalent to the call
*
* {@link #ALL} and {@link #OFF}
* are simple markers with severities mapped respectively to
* {@link java.lang.Integer#MIN_VALUE Integer.MIN_VALUE} and
* {@link java.lang.Integer#MAX_VALUE Integer.MAX_VALUE}.
*
The mapping is as follows:
*
*
*
*
* @since 9
*
* @see java.lang.System.LoggerFinder
* @see java.lang.System.Logger
*/
public enum Level {
// for convenience, we're reusing java.util.logging.Level int values
// the mapping logic in sun.util.logging.PlatformLogger depends
// on this.
/**
* A marker to indicate that all levels are enabled.
* This level {@linkplain #getSeverity() severity} is
* {@link Integer#MIN_VALUE}.
*/
ALL(Integer.MIN_VALUE), // typically mapped to/from j.u.l.Level.ALL
/**
* {@code TRACE} level: usually used to log diagnostic information.
* This level {@linkplain #getSeverity() severity} is
* {@code 400}.
*/
TRACE(400), // typically mapped to/from j.u.l.Level.FINER
/**
* {@code DEBUG} level: usually used to log debug information traces.
* This level {@linkplain #getSeverity() severity} is
* {@code 500}.
*/
DEBUG(500), // typically mapped to/from j.u.l.Level.FINEST/FINE/CONFIG
/**
* {@code INFO} level: usually used to log information messages.
* This level {@linkplain #getSeverity() severity} is
* {@code 800}.
*/
INFO(800), // typically mapped to/from j.u.l.Level.INFO
/**
* {@code WARNING} level: usually used to log warning messages.
* This level {@linkplain #getSeverity() severity} is
* {@code 900}.
*/
WARNING(900), // typically mapped to/from j.u.l.Level.WARNING
/**
* {@code ERROR} level: usually used to log error messages.
* This level {@linkplain #getSeverity() severity} is
* {@code 1000}.
*/
ERROR(1000), // typically mapped to/from j.u.l.Level.SEVERE
/**
* A marker to indicate that all levels are disabled.
* This level {@linkplain #getSeverity() severity} is
* {@link Integer#MAX_VALUE}.
*/
OFF(Integer.MAX_VALUE); // typically mapped to/from j.u.l.Level.OFF
private final int severity;
private Level(int severity) {
this.severity = severity;
}
/**
* Returns the name of this level.
* @return this level {@linkplain #name()}.
*/
public final String getName() {
return name();
}
/**
* Returns the severity of this level.
* A higher severity means a more severe condition.
* @return this level severity.
*/
public final int getSeverity() {
return severity;
}
}
/**
* Returns the name of this logger.
*
* @return the logger name.
*/
public String getName();
/**
* Checks if a message of the given level would be logged by
* this logger.
*
* @param level the log message level.
* @return {@code true} if the given log message level is currently
* being logged.
*
* @throws NullPointerException if {@code level} is {@code null}.
*/
public boolean isLoggable(Level level);
/**
* Logs a message.
*
* @implSpec The default implementation for this method calls
* {@code this.log(level, (ResourceBundle)null, msg, (Object[])null);}
*
* @param level the log message level.
* @param msg the string message (or a key in the message catalog, if
* this logger is a {@link
* LoggerFinder#getLocalizedLogger(java.lang.String,
* java.util.ResourceBundle, java.lang.Module) localized logger});
* can be {@code null}.
*
* @throws NullPointerException if {@code level} is {@code null}.
*/
public default void log(Level level, String msg) {
log(level, (ResourceBundle) null, msg, (Object[]) null);
}
/**
* Logs a lazily supplied message.
*
* If the logger is currently enabled for the given log message level
* then a message is logged that is the result produced by the
* given supplier function. Otherwise, the supplier is not operated on.
*
* @implSpec When logging is enabled for the given level, the default
* implementation for this method calls
* {@code this.log(level, (ResourceBundle)null, msgSupplier.get(), (Object[])null);}
*
* @param level the log message level.
* @param msgSupplier a supplier function that produces a message.
*
* @throws NullPointerException if {@code level} is {@code null},
* or {@code msgSupplier} is {@code null}.
*/
public default void log(Level level, SupplierSystem.Logger Levels
* java.util.logging Levels
* {@link Logger.Level#ALL ALL}
* {@link java.util.logging.Level#ALL ALL}
* {@link Logger.Level#TRACE TRACE}
* {@link java.util.logging.Level#FINER FINER}
* {@link Logger.Level#DEBUG DEBUG}
* {@link java.util.logging.Level#FINE FINE}
* {@link Logger.Level#INFO INFO}
* {@link java.util.logging.Level#INFO INFO}
* {@link Logger.Level#WARNING WARNING}
* {@link java.util.logging.Level#WARNING WARNING}
* {@link Logger.Level#ERROR ERROR}
* {@link java.util.logging.Level#SEVERE SEVERE}
* {@link Logger.Level#OFF OFF}
* {@link java.util.logging.Level#OFF OFF}
*
*
*
* It is the responsibility of the provider of
* the concrete {@code LoggerFinder} implementation to ensure that
* these loggers are not configured by untrusted code without proper
* permission checks, as configuration performed on such loggers usually
* affects all applications in the same Java Runtime.
*
The default LoggerFinder using {@code java.util.logging} as the backend
* maps {@code System.Logger} levels to
* {@linkplain java.util.logging.Level java.util.logging} levels
* of corresponding severity - as described in {@link Logger.Level
* Logger.Level}.
*
* @see java.lang.System
* @see java.lang.System.Logger
*
* @since 9
*/
public static abstract class LoggerFinder {
/**
* The {@code RuntimePermission("loggerFinder")} is
* necessary to subclass and instantiate the {@code LoggerFinder} class,
* as well as to obtain loggers from an instance of that class.
*/
static final RuntimePermission LOGGERFINDER_PERMISSION =
new RuntimePermission("loggerFinder");
/**
* Creates a new instance of {@code LoggerFinder}.
*
* @implNote It is recommended that a {@code LoggerFinder} service
* implementation does not perform any heavy initialization in its
* constructor, in order to avoid possible risks of deadlock or class
* loading cycles during the instantiation of the service provider.
*
* @throws SecurityException if a security manager is present and its
* {@code checkPermission} method doesn't allow the
* {@code RuntimePermission("loggerFinder")}.
*/
protected LoggerFinder() {
this(checkPermission());
}
private LoggerFinder(Void unused) {
// nothing to do.
}
private static Void checkPermission() {
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
sm.checkPermission(LOGGERFINDER_PERMISSION);
}
return null;
}
/**
* Returns an instance of {@link Logger Logger}
* for the given {@code module}.
*
* @param name the name of the logger.
* @param module the module for which the logger is being requested.
*
* @return a {@link Logger logger} suitable for use within the given
* module.
* @throws NullPointerException if {@code name} is {@code null} or
* {@code module} is {@code null}.
* @throws SecurityException if a security manager is present and its
* {@code checkPermission} method doesn't allow the
* {@code RuntimePermission("loggerFinder")}.
*/
public abstract Logger getLogger(String name, Module module);
/**
* Returns a localizable instance of {@link Logger Logger}
* for the given {@code module}.
* The returned logger will use the provided resource bundle for
* message localization.
*
* @implSpec By default, this method calls {@link
* #getLogger(java.lang.String, java.lang.Module)
* this.getLogger(name, module)} to obtain a logger, then wraps that
* logger in a {@link Logger} instance where all methods that do not
* take a {@link ResourceBundle} as parameter are redirected to one
* which does - passing the given {@code bundle} for
* localization. So for instance, a call to {@link
* Logger#log(Logger.Level, String) Logger.log(Level.INFO, msg)}
* will end up as a call to {@link
* Logger#log(Logger.Level, ResourceBundle, String, Object...)
* Logger.log(Level.INFO, bundle, msg, (Object[])null)} on the wrapped
* logger instance.
* Note however that by default, string messages returned by {@link
* java.util.function.Supplier Supplier<String>} will not be
* localized, as it is assumed that such strings are messages which are
* already constructed, rather than keys in a resource bundle.
*
*
* @param status exit status.
* @throws SecurityException
* if a security manager exists and its {@code checkExit}
* method doesn't allow exit with the specified status.
* @see java.lang.Runtime#exit(int)
*/
public static void exit(int status) {
Runtime.getRuntime().exit(status);
}
/**
* Runs the garbage collector.
*
* Calling the {@code gc} method suggests that the Java Virtual
* Machine expend effort toward recycling unused objects in order to
* make the memory they currently occupy available for quick reuse.
* When control returns from the method call, the Java Virtual
* Machine has made a best effort to reclaim space from all discarded
* objects.
*
* Runtime.getRuntime().exit(n)
*
*
* @see java.lang.Runtime#gc()
*/
public static void gc() {
Runtime.getRuntime().gc();
}
/**
* Runs the finalization methods of any objects pending finalization.
*
* Calling this method suggests that the Java Virtual Machine expend
* effort toward running the {@code finalize} methods of objects
* that have been found to be discarded but whose {@code finalize}
* methods have not yet been run. When control returns from the
* method call, the Java Virtual Machine has made a best effort to
* complete all outstanding finalizations.
*
* Runtime.getRuntime().gc()
*
*
* @see java.lang.Runtime#runFinalization()
*/
public static void runFinalization() {
Runtime.getRuntime().runFinalization();
}
/**
* Loads the native library specified by the filename argument. The filename
* argument must be an absolute path name.
*
* If the filename argument, when stripped of any platform-specific library
* prefix, path, and file extension, indicates a library whose name is,
* for example, L, and a native library called L is statically linked
* with the VM, then the JNI_OnLoad_L function exported by the library
* is invoked rather than attempting to load a dynamic library.
* A filename matching the argument does not have to exist in the
* file system.
* See the JNI Specification
* for more details.
*
* Otherwise, the filename argument is mapped to a native library image in
* an implementation-dependent manner.
*
*
* Runtime.getRuntime().runFinalization()
*
*
* @param filename the file to load.
* @throws SecurityException if a security manager exists and its
* {@code checkLink} method doesn't allow
* loading of the specified dynamic library
* @throws UnsatisfiedLinkError if either the filename is not an
* absolute path name, the native library is not statically
* linked with the VM, or the library cannot be mapped to
* a native library image by the host system.
* @throws NullPointerException if {@code filename} is {@code null}
* @see java.lang.Runtime#load(java.lang.String)
* @see java.lang.SecurityManager#checkLink(java.lang.String)
*/
@CallerSensitive
public static void load(String filename) {
Runtime.getRuntime().load0(Reflection.getCallerClass(), filename);
}
/**
* Loads the native library specified by the {@code libname}
* argument. The {@code libname} argument must not contain any platform
* specific prefix, file extension or path. If a native library
* called {@code libname} is statically linked with the VM, then the
* JNI_OnLoad_{@code libname} function exported by the library is invoked.
* See the JNI Specification
* for more details.
*
* Otherwise, the libname argument is loaded from a system library
* location and mapped to a native library image in an implementation-
* dependent manner.
*
* Runtime.getRuntime().load(name)
*
*
* @param libname the name of the library.
* @throws SecurityException if a security manager exists and its
* {@code checkLink} method doesn't allow
* loading of the specified dynamic library
* @throws UnsatisfiedLinkError if either the libname argument
* contains a file path, the native library is not statically
* linked with the VM, or the library cannot be mapped to a
* native library image by the host system.
* @throws NullPointerException if {@code libname} is {@code null}
* @see java.lang.Runtime#loadLibrary(java.lang.String)
* @see java.lang.SecurityManager#checkLink(java.lang.String)
*/
@CallerSensitive
public static void loadLibrary(String libname) {
Runtime.getRuntime().loadLibrary0(Reflection.getCallerClass(), libname);
}
/**
* Maps a library name into a platform-specific string representing
* a native library.
*
* @param libname the name of the library.
* @return a platform-dependent native library name.
* @throws NullPointerException if {@code libname} is {@code null}
* @see java.lang.System#loadLibrary(java.lang.String)
* @see java.lang.ClassLoader#findLibrary(java.lang.String)
* @since 1.2
*/
public static native String mapLibraryName(String libname);
/**
* Create PrintStream for stdout/err based on encoding.
*/
private static PrintStream newPrintStream(FileOutputStream fos, String enc) {
if (enc != null) {
try {
return new PrintStream(new BufferedOutputStream(fos, 128), true, enc);
} catch (UnsupportedEncodingException uee) {}
}
return new PrintStream(new BufferedOutputStream(fos, 128), true);
}
/**
* Logs an exception/error at initialization time to stdout or stderr.
*
* @param printToStderr to print to stderr rather than stdout
* @param printStackTrace to print the stack trace
* @param msg the message to print before the exception, can be {@code null}
* @param e the exception or error
*/
private static void logInitException(boolean printToStderr,
boolean printStackTrace,
String msg,
Throwable e) {
if (VM.initLevel() < 1) {
throw new InternalError("system classes not initialized");
}
PrintStream log = (printToStderr) ? err : out;
if (msg != null) {
log.println(msg);
}
if (printStackTrace) {
e.printStackTrace(log);
} else {
log.println(e);
for (Throwable suppressed : e.getSuppressed()) {
log.println("Suppressed: " + suppressed);
}
Throwable cause = e.getCause();
if (cause != null) {
log.println("Caused by: " + cause);
}
}
}
/**
* Create the Properties object from a map - masking out system properties
* that are not intended for public access.
*/
private static Properties createProperties(Map
* Runtime.getRuntime().loadLibrary(name)
*