Every {@link java.lang.Class Class} object contains a {@link * Class#getClassLoader() reference} to the {@code ClassLoader} that defined * it. * *
{@code Class} objects for array classes are not created by class * loaders, but are created automatically as required by the Java runtime. * The class loader for an array class, as returned by {@link * Class#getClassLoader()} is the same as the class loader for its element * type; if the element type is a primitive type, then the array class has no * class loader. * *
Applications implement subclasses of {@code ClassLoader} in order to * extend the manner in which the Java virtual machine dynamically loads * classes. * *
Class loaders may typically be used by security managers to indicate * security domains. * *
In addition to loading classes, a class loader is also responsible for * locating resources. A resource is some data (a "{@code .class}" file, * configuration data, or an image for example) that is identified with an * abstract '/'-separated path name. Resources are typically packaged with an * application or library so that they can be located by code in the * application or library. In some cases, the resources are included so that * they can be located by other libraries. * *
The {@code ClassLoader} class uses a delegation model to search for * classes and resources. Each instance of {@code ClassLoader} has an * associated parent class loader. When requested to find a class or * resource, a {@code ClassLoader} instance will usually delegate the search * for the class or resource to its parent class loader before attempting to * find the class or resource itself. * *
Class loaders that support concurrent loading of classes are known as * {@linkplain #isRegisteredAsParallelCapable() parallel capable} class * loaders and are required to register themselves at their class initialization * time by invoking the {@link * #registerAsParallelCapable ClassLoader.registerAsParallelCapable} * method. Note that the {@code ClassLoader} class is registered as parallel * capable by default. However, its subclasses still need to register themselves * if they are parallel capable. * In environments in which the delegation model is not strictly * hierarchical, class loaders need to be parallel capable, otherwise class * loading can lead to deadlocks because the loader lock is held for the * duration of the class loading process (see {@link #loadClass * loadClass} methods). * *
Bootstrap class loader. * It is the virtual machine's built-in class loader, typically represented * as {@code null}, and does not have a parent.
{@linkplain #getPlatformClassLoader() Platform class loader}. * All platform classes are visible to the platform class loader * that can be used as the parent of a {@code ClassLoader} instance. * Platform classes include Java SE platform APIs, their implementation * classes and JDK-specific run-time classes that are defined by the * platform class loader or its ancestors. *
To allow for upgrading/overriding of modules defined to the platform * class loader, and where upgraded modules read modules defined to class * loaders other than the platform class loader and its ancestors, then * the platform class loader may have to delegate to other class loaders, * the application class loader for example. * In other words, classes in named modules defined to class loaders * other than the platform class loader and its ancestors may be visible * to the platform class loader.
{@linkplain #getSystemClassLoader() System class loader}. * It is also known as application class loader and is distinct * from the platform class loader. * The system class loader is typically used to define classes on the * application class path, module path, and JDK-specific tools. * The platform class loader is a parent or an ancestor of the system class * loader that all platform classes are visible to it.
Normally, the Java virtual machine loads classes from the local file * system in a platform-dependent manner. * However, some classes may not originate from a file; they may originate * from other sources, such as the network, or they could be constructed by an * application. The method {@link #defineClass(String, byte[], int, int) * defineClass} converts an array of bytes into an instance of class * {@code Class}. Instances of this newly defined class can be created using * {@link Class#newInstance Class.newInstance}. * *
The methods and constructors of objects created by a class loader may * reference other classes. To determine the class(es) referred to, the Java * virtual machine invokes the {@link #loadClass loadClass} method of * the class loader that originally created the class. * *
For example, an application could create a network class loader to * download class files from a server. Sample code might look like: * *
* ClassLoader loader = new NetworkClassLoader(host, port);
* Object main = loader.loadClass("Main", true).newInstance();
* . . .
* The network class loader subclass must define the methods {@link * #findClass findClass} and {@code loadClassData} to load a class * from the network. Once it has downloaded the bytes that make up the class, * it should use the method {@link #defineClass defineClass} to * create a class instance. A sample implementation is: * *
* class NetworkClassLoader extends ClassLoader {
* String host;
* int port;
*
* public Class findClass(String name) {
* byte[] b = loadClassData(name);
* return defineClass(name, b, 0, b.length);
* }
*
* private byte[] loadClassData(String name) {
* // load the class data from the connection
* . . .
* }
* }
* Any class name provided as a {@code String} parameter to methods in * {@code ClassLoader} must be a binary name as defined by * The Java™ Language Specification. * *
Examples of valid class names include: *
* ** "java.lang.String" * "javax.swing.JSpinner$DefaultEditor" * "java.security.KeyStore$Builder$FileBuilder$1" * "java.net.URLClassLoader$3$1" *
Any package name provided as a {@code String} parameter to methods in
* {@code ClassLoader} must be either the empty string (denoting an unnamed package)
* or a fully qualified name as defined by
* The Java™ Language Specification.
*
* @jls 6.7 Fully Qualified Names
* @jls 13.1 The Form of a Binary
* @see #resolveClass(Class)
* @since 1.0
* @revised 9
* @spec JPMS
*/
public abstract class ClassLoader {
private static native void registerNatives();
static {
registerNatives();
}
// The parent class loader for delegation
// Note: VM hardcoded the offset of this field, thus all new fields
// must be added *after* it.
private final ClassLoader parent;
// class loader name
private final String name;
// the unnamed module for this ClassLoader
private final Module unnamedModule;
/**
* Encapsulates the set of parallel capable loader types.
*/
private static class ParallelLoaders {
private ParallelLoaders() {}
// the set of parallel capable loader types
private static final Set If there is a security manager, its {@link
* SecurityManager#checkCreateClassLoader() checkCreateClassLoader} method
* is invoked. This may result in a security exception. If there is a security manager, its {@link
* SecurityManager#checkCreateClassLoader()
* checkCreateClassLoader} method is invoked. This may result in
* a security exception. Invoke {@link #findLoadedClass(String)} to check if the class
* has already been loaded. Invoke the {@link #loadClass(String) loadClass} method
* on the parent class loader. If the parent is {@code null} the class
* loader built into the virtual machine is used, instead. Invoke the {@link #findClass(String)} method to find the
* class. If the class was found using the above steps, and the
* {@code resolve} flag is true, this method will then invoke the {@link
* #resolveClass(Class)} method on the resulting {@code Class} object.
*
* Subclasses of {@code ClassLoader} are encouraged to override {@link
* #findClass(String)}, rather than this method. Unless overridden, this method synchronizes on the result of
* {@link #getClassLoadingLock getClassLoadingLock} method
* during the entire class loading process.
*
* @param name
* The binary name of the class
*
* @param resolve
* If {@code true} then resolve the class
*
* @return The resulting {@code Class} object
*
* @throws ClassNotFoundException
* If the class could not be found
*/
protected Class loadClass(String name, boolean resolve)
throws ClassNotFoundException
{
synchronized (getClassLoadingLock(name)) {
// First, check if the class has already been loaded
Class c = findLoadedClass(name);
if (c == null) {
long t0 = System.nanoTime();
try {
if (parent != null) {
c = parent.loadClass(name, false);
} else {
c = findBootstrapClassOrNull(name);
}
} catch (ClassNotFoundException e) {
// ClassNotFoundException thrown if class not found
// from the non-null parent class loader
}
if (c == null) {
// If still not found, then invoke findClass in order
// to find the class.
long t1 = System.nanoTime();
c = findClass(name);
// this is the defining class loader; record the stats
PerfCounter.getParentDelegationTime().addTime(t1 - t0);
PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
PerfCounter.getFindClasses().increment();
}
}
if (resolve) {
resolveClass(c);
}
return c;
}
}
/**
* Loads the class with the specified binary name
* in a module defined to this class loader. This method returns {@code null}
* if the class could not be found.
*
* @apiNote This method does not delegate to the parent class loader.
*
* @implSpec The default implementation of this method searches for classes
* in the following order:
*
* This method assigns a default {@link java.security.ProtectionDomain
* ProtectionDomain} to the newly defined class. The
* {@code ProtectionDomain} is effectively granted the same set of
* permissions returned when {@link
* java.security.Policy#getPermissions(java.security.CodeSource)
* Policy.getPolicy().getPermissions(new CodeSource(null, null))}
* is invoked. The default protection domain is created on the first invocation
* of {@link #defineClass(String, byte[], int, int) defineClass},
* and re-used on subsequent invocations.
*
* To assign a specific {@code ProtectionDomain} to the class, use
* the {@link #defineClass(String, byte[], int, int,
* java.security.ProtectionDomain) defineClass} method that takes a
* {@code ProtectionDomain} as one of its arguments.
* This method defines a package in this class loader corresponding to the
* package of the {@code Class} (if such a package has not already been defined
* in this class loader). The name of the defined package is derived from
* the binary name of the class specified by
* the byte array {@code b}.
* Other properties of the defined package are as specified by {@link Package}.
*
* @param name
* The expected binary name of the class, or
* {@code null} if not known
*
* @param b
* The bytes that make up the class data. The bytes in positions
* {@code off} through {@code off+len-1} should have the format
* of a valid class file as defined by
* The Java™ Virtual Machine Specification.
*
* @param off
* The start offset in {@code b} of the class data
*
* @param len
* The length of the class data
*
* @return The {@code Class} object that was created from the specified
* class data.
*
* @throws ClassFormatError
* If the data did not contain a valid class
*
* @throws IndexOutOfBoundsException
* If either {@code off} or {@code len} is negative, or if
* {@code off+len} is greater than {@code b.length}.
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class (which is unsigned), or if
* {@code name} begins with "{@code java.}".
*
* @see #loadClass(String, boolean)
* @see #resolveClass(Class)
* @see java.security.CodeSource
* @see java.security.SecureClassLoader
*
* @since 1.1
* @revised 9
* @spec JPMS
*/
protected final Class defineClass(String name, byte[] b, int off, int len)
throws ClassFormatError
{
return defineClass(name, b, off, len, null);
}
/* Determine protection domain, and check that:
- not define java.* class,
- signer of this class matches signers for the rest of the classes in
package.
*/
private ProtectionDomain preDefineClass(String name,
ProtectionDomain pd)
{
if (!checkName(name))
throw new NoClassDefFoundError("IllegalName: " + name);
// Note: Checking logic in java.lang.invoke.MemberName.checkForTypeAlias
// relies on the fact that spoofing is impossible if a class has a name
// of the form "java.*"
if ((name != null) && name.startsWith("java.")
&& this != getBuiltinPlatformClassLoader()) {
throw new SecurityException
("Prohibited package name: " +
name.substring(0, name.lastIndexOf('.')));
}
if (pd == null) {
pd = defaultDomain;
}
if (name != null) {
checkCerts(name, pd.getCodeSource());
}
return pd;
}
private String defineClassSourceLocation(ProtectionDomain pd) {
CodeSource cs = pd.getCodeSource();
String source = null;
if (cs != null && cs.getLocation() != null) {
source = cs.getLocation().toString();
}
return source;
}
private void postDefineClass(Class c, ProtectionDomain pd) {
// define a named package, if not present
getNamedPackage(c.getPackageName(), c.getModule());
if (pd.getCodeSource() != null) {
Certificate certs[] = pd.getCodeSource().getCertificates();
if (certs != null)
setSigners(c, certs);
}
}
/**
* Converts an array of bytes into an instance of class {@code Class},
* with a given {@code ProtectionDomain}.
*
* If the given {@code ProtectionDomain} is {@code null},
* then a default protection domain will be assigned to the class as specified
* in the documentation for {@link #defineClass(String, byte[], int, int)}.
* Before the class can be used it must be resolved.
*
* The first class defined in a package determines the exact set of
* certificates that all subsequent classes defined in that package must
* contain. The set of certificates for a class is obtained from the
* {@link java.security.CodeSource CodeSource} within the
* {@code ProtectionDomain} of the class. Any classes added to that
* package must contain the same set of certificates or a
* {@code SecurityException} will be thrown. Note that if
* {@code name} is {@code null}, this check is not performed.
* You should always pass in the binary name of the
* class you are defining as well as the bytes. This ensures that the
* class you are defining is indeed the class you think it is.
*
* If the specified {@code name} begins with "{@code java.}", it can
* only be defined by the {@linkplain #getPlatformClassLoader()
* platform class loader} or its ancestors; otherwise {@code SecurityException}
* will be thrown. If {@code name} is not {@code null}, it must be equal to
* the binary name of the class
* specified by the byte array {@code b}, otherwise a {@link
* NoClassDefFoundError NoClassDefFoundError} will be thrown.
*
* This method defines a package in this class loader corresponding to the
* package of the {@code Class} (if such a package has not already been defined
* in this class loader). The name of the defined package is derived from
* the binary name of the class specified by
* the byte array {@code b}.
* Other properties of the defined package are as specified by {@link Package}.
*
* @param name
* The expected binary name of the class, or
* {@code null} if not known
*
* @param b
* The bytes that make up the class data. The bytes in positions
* {@code off} through {@code off+len-1} should have the format
* of a valid class file as defined by
* The Java™ Virtual Machine Specification.
*
* @param off
* The start offset in {@code b} of the class data
*
* @param len
* The length of the class data
*
* @param protectionDomain
* The {@code ProtectionDomain} of the class
*
* @return The {@code Class} object created from the data,
* and {@code ProtectionDomain}.
*
* @throws ClassFormatError
* If the data did not contain a valid class
*
* @throws NoClassDefFoundError
* If {@code name} is not {@code null} and not equal to the
* binary name of the class specified by {@code b}
*
* @throws IndexOutOfBoundsException
* If either {@code off} or {@code len} is negative, or if
* {@code off+len} is greater than {@code b.length}.
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class, or if {@code name} begins with
* "{@code java.}" and this class loader is not the platform
* class loader or its ancestor.
*
* @revised 9
* @spec JPMS
*/
protected final Class defineClass(String name, byte[] b, int off, int len,
ProtectionDomain protectionDomain)
throws ClassFormatError
{
protectionDomain = preDefineClass(name, protectionDomain);
String source = defineClassSourceLocation(protectionDomain);
Class c = defineClass1(this, name, b, off, len, protectionDomain, source);
postDefineClass(c, protectionDomain);
return c;
}
/**
* Converts a {@link java.nio.ByteBuffer ByteBuffer} into an instance
* of class {@code Class}, with the given {@code ProtectionDomain}.
* If the given {@code ProtectionDomain} is {@code null}, then a default
* protection domain will be assigned to the class as
* specified in the documentation for {@link #defineClass(String, byte[],
* int, int)}. Before the class can be used it must be resolved.
*
* The rules about the first class defined in a package determining the
* set of certificates for the package, the restrictions on class names,
* and the defined package of the class
* are identical to those specified in the documentation for {@link
* #defineClass(String, byte[], int, int, ProtectionDomain)}.
*
* An invocation of this method of the form
* cl{@code .defineClass(}name{@code ,}
* bBuffer{@code ,} pd{@code )} yields exactly the same
* result as the statements
*
* This method loads the class through the system class loader (see
* {@link #getSystemClassLoader()}). The {@code Class} object returned
* might have more than one {@code ClassLoader} associated with it.
* Subclasses of {@code ClassLoader} need not usually invoke this method,
* because most class loaders need to override just {@link
* #findClass(String)}. The name of a resource is a '{@code /}'-separated path name that
* identifies the resource. Resources in named modules are subject to the encapsulation rules
* specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
* Additionally, and except for the special case where the resource has a
* name ending with "{@code .class}", this method will only find resources in
* packages of named modules when the package is {@link Module#isOpen(String)
* opened} unconditionally (even if the caller of this method is in the
* same module as the resource). The name of a resource is a {@code /}-separated path name that
* identifies the resource. Resources in named modules are subject to the encapsulation rules
* specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
* Additionally, and except for the special case where the resource has a
* name ending with "{@code .class}", this method will only find resources in
* packages of named modules when the package is {@link Module#isOpen(String)
* opened} unconditionally (even if the caller of this method is in the
* same module as the resource). The name of a resource is a {@code /}-separated path name that
* identifies the resource.
*
* The resources will be located when the returned stream is evaluated.
* If the evaluation results in an {@code IOException} then the I/O
* exception is wrapped in an {@link UncheckedIOException} that is then
* thrown.
*
* Resources in named modules are subject to the encapsulation rules
* specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
* Additionally, and except for the special case where the resource has a
* name ending with "{@code .class}", this method will only find resources in
* packages of named modules when the package is {@link Module#isOpen(String)
* opened} unconditionally (even if the caller of this method is in the
* same module as the resource). For resources in named modules then the method must implement the
* rules for encapsulation specified in the {@code Module} {@link
* Module#getResourceAsStream getResourceAsStream} method. Additionally,
* it must not find non-"{@code .class}" resources in packages of named
* modules unless the package is {@link Module#isOpen(String) opened}
* unconditionally. For resources in named modules then the method must implement the
* rules for encapsulation specified in the {@code Module} {@link
* Module#getResourceAsStream getResourceAsStream} method. Additionally,
* it must not find non-"{@code .class}" resources in packages of named
* modules unless the package is {@link Module#isOpen(String) opened}
* unconditionally. Note that once a class loader is registered as parallel capable, there
* is no way to change it back. Resources in named modules are subject to the encapsulation rules
* specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
* Additionally, and except for the special case where the resource has a
* name ending with "{@code .class}", this method will only find resources in
* packages of named modules when the package is {@link Module#isOpen(String)
* opened} unconditionally. The search order is described in the documentation for {@link
* #getSystemResource(String)}. Resources in named modules are subject to the encapsulation rules
* specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
* Additionally, and except for the special case where the resource has a
* name ending with "{@code .class}", this method will only find resources in
* packages of named modules when the package is {@link Module#isOpen(String)
* opened} unconditionally. The search order is described in the documentation for {@link
* #getResource(String)}. Resources in named modules are subject to the encapsulation rules
* specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
* Additionally, and except for the special case where the resource has a
* name ending with "{@code .class}", this method will only find resources in
* packages of named modules when the package is {@link Module#isOpen(String)
* opened} unconditionally. Resources in named modules are subject to the encapsulation rules
* specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
* Additionally, and except for the special case where the resource has a
* name ending with "{@code .class}", this method will only find resources in
* packages of named modules when the package is {@link Module#isOpen(String)
* opened} unconditionally. This method is first invoked early in the runtime's startup
* sequence, at which point it creates the system class loader. This
* class loader will be the context class loader for the main application
* thread (for example, the thread that invokes the {@code main} method of
* the main class).
*
* The default system class loader is an implementation-dependent
* instance of this class.
*
* If the system property "{@code java.system.class.loader}" is defined
* when this method is first invoked then the value of that property is
* taken to be the name of a class that will be returned as the system
* class loader. The class is loaded using the default system class loader
* and must define a public constructor that takes a single parameter of
* type {@code ClassLoader} which is used as the delegation parent. An
* instance is then created using this constructor with the default system
* class loader as the parameter. The resulting class loader is defined
* to be the system class loader. During construction, the class loader
* should take great care to avoid calling {@code getSystemClassLoader()}.
* If circular initialization of the system class loader is detected then
* an unspecified error or exception is thrown.
*
* @implNote The system property to override the system class loader is not
* examined until the VM is almost fully initialized. Code that executes
* this method during startup should take care not to cache the return
* value until the system is fully initialized.
*
* The name of the built-in system class loader is {@code "app"}.
* The class path used by the built-in system class loader is determined
* by the system property "{@code java.class.path}" during early
* initialization of the VM. If the system property is not defined,
* or its value is an empty string, then there is no class path
* when the initial module is a module on the application module path,
* i.e. a named module. If the initial module is not on
* the application module path then the class path defaults to
* the current working directory.
*
* @return The system {@code ClassLoader} for delegation
*
* @throws SecurityException
* If a security manager is present, and the caller's class loader
* is not {@code null} and is not the same as or an ancestor of the
* system class loader, and the caller does not have the
* {@link RuntimePermission}{@code ("getClassLoader")}
*
* @throws IllegalStateException
* If invoked recursively during the construction of the class
* loader specified by the "{@code java.system.class.loader}"
* property.
*
* @throws Error
* If the system property "{@code java.system.class.loader}"
* is defined but the named class could not be loaded, the
* provider class does not define the required constructor, or an
* exception is thrown by that constructor when it is invoked. The
* underlying cause of the error can be retrieved via the
* {@link Throwable#getCause()} method.
*
* @revised 1.4
* @revised 9
* @spec JPMS
*/
@CallerSensitive
public static ClassLoader getSystemClassLoader() {
switch (VM.initLevel()) {
case 0:
case 1:
case 2:
// the system class loader is the built-in app class loader during startup
return getBuiltinAppClassLoader();
case 3:
String msg = "getSystemClassLoader should only be called after VM booted";
throw new InternalError(msg);
case 4:
// system fully initialized
assert VM.isBooted() && scl != null;
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkClassLoaderPermission(scl, Reflection.getCallerClass());
}
return scl;
default:
throw new InternalError("should not reach here");
}
}
static ClassLoader getBuiltinPlatformClassLoader() {
return ClassLoaders.platformClassLoader();
}
static ClassLoader getBuiltinAppClassLoader() {
return ClassLoaders.appClassLoader();
}
/*
* Initialize the system class loader that may be a custom class on the
* application class path or application module path.
*
* @see java.lang.System#initPhase3
*/
static synchronized ClassLoader initSystemClassLoader() {
if (VM.initLevel() != 3) {
throw new InternalError("system class loader cannot be set at initLevel " +
VM.initLevel());
}
// detect recursive initialization
if (scl != null) {
throw new IllegalStateException("recursive invocation");
}
ClassLoader builtinLoader = getBuiltinAppClassLoader();
// All are privileged frames. No need to call doPrivileged.
String cn = System.getProperty("java.system.class.loader");
if (cn != null) {
try {
// custom class loader is only supported to be loaded from unnamed module
Constructor ctor = Class.forName(cn, false, builtinLoader)
.getDeclaredConstructor(ClassLoader.class);
scl = (ClassLoader) ctor.newInstance(builtinLoader);
} catch (Exception e) {
throw new Error(e);
}
} else {
scl = builtinLoader;
}
return scl;
}
// Returns true if the specified class loader can be found in this class
// loader's delegation chain.
boolean isAncestor(ClassLoader cl) {
ClassLoader acl = this;
do {
acl = acl.parent;
if (cl == acl) {
return true;
}
} while (acl != null);
return false;
}
// Tests if class loader access requires "getClassLoader" permission
// check. A class loader 'from' can access class loader 'to' if
// class loader 'from' is same as class loader 'to' or an ancestor
// of 'to'. The class loader in a system domain can access
// any class loader.
private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
ClassLoader to)
{
if (from == to)
return false;
if (from == null)
return false;
return !to.isAncestor(from);
}
// Returns the class's class loader, or null if none.
static ClassLoader getClassLoader(Class caller) {
// This can be null if the VM is requesting it
if (caller == null) {
return null;
}
// Circumvent security check since this is package-private
return caller.getClassLoader0();
}
/*
* Checks RuntimePermission("getClassLoader") permission
* if caller's class loader is not null and caller's class loader
* is not the same as or an ancestor of the given cl argument.
*/
static void checkClassLoaderPermission(ClassLoader cl, Class caller) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
// caller can be null if the VM is requesting it
ClassLoader ccl = getClassLoader(caller);
if (needsClassLoaderPermissionCheck(ccl, cl)) {
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
}
}
}
// The system class loader
// @GuardedBy("ClassLoader.class")
private static volatile ClassLoader scl;
// -- Package --
/**
* Define a Package of the given Class object.
*
* If the given class represents an array type, a primitive type or void,
* this method returns {@code null}.
*
* This method does not throw IllegalArgumentException.
*/
Package definePackage(Class c) {
if (c.isPrimitive() || c.isArray()) {
return null;
}
return definePackage(c.getPackageName(), c.getModule());
}
/**
* Defines a Package of the given name and module
*
* This method does not throw IllegalArgumentException.
*
* @param name package name
* @param m module
*/
Package definePackage(String name, Module m) {
if (name.isEmpty() && m.isNamed()) {
throw new InternalError("unnamed package in " + m);
}
// check if Package object is already defined
NamedPackage pkg = packages.get(name);
if (pkg instanceof Package)
return (Package)pkg;
return (Package)packages.compute(name, (n, p) -> toPackage(n, p, m));
}
/*
* Returns a Package object for the named package
*/
private Package toPackage(String name, NamedPackage p, Module m) {
// define Package object if the named package is not yet defined
if (p == null)
return NamedPackage.toPackage(name, m);
// otherwise, replace the NamedPackage object with Package object
if (p instanceof Package)
return (Package)p;
return NamedPackage.toPackage(p.packageName(), p.module());
}
/**
* Defines a package by name in this {@code ClassLoader}.
*
* Package names must be unique within a class loader and
* cannot be redefined or changed once created.
*
* If a class loader wishes to define a package with specific properties,
* such as version information, then the class loader should call this
* {@code definePackage} method before calling {@code defineClass}.
* Otherwise, the
* {@link #defineClass(String, byte[], int, int, ProtectionDomain) defineClass}
* method will define a package in this class loader corresponding to the package
* of the newly defined class; the properties of this defined package are
* specified by {@link Package}.
*
* @apiNote
* A class loader that wishes to define a package for classes in a JAR
* typically uses the specification and implementation titles, versions, and
* vendors from the JAR's manifest. If the package is specified as
* {@linkplain java.util.jar.Attributes.Name#SEALED sealed} in the JAR's manifest,
* the {@code URL} of the JAR file is typically used as the {@code sealBase}.
* If classes of package {@code 'p'} defined by this class loader
* are loaded from multiple JARs, the {@code Package} object may contain
* different information depending on the first class of package {@code 'p'}
* defined and which JAR's manifest is read first to explicitly define
* package {@code 'p'}.
*
* It is strongly recommended that a class loader does not call this
* method to explicitly define packages in named modules; instead,
* the package will be automatically defined when a class is {@linkplain
* #defineClass(String, byte[], int, int, ProtectionDomain) being defined}.
* If it is desirable to define {@code Package} explicitly, it should ensure
* that all packages in a named module are defined with the properties
* specified by {@link Package}. Otherwise, some {@code Package} objects
* in a named module may be for example sealed with different seal base.
*
* @param name
* The package name
*
* @param specTitle
* The specification title
*
* @param specVersion
* The specification version
*
* @param specVendor
* The specification vendor
*
* @param implTitle
* The implementation title
*
* @param implVersion
* The implementation version
*
* @param implVendor
* The implementation vendor
*
* @param sealBase
* If not {@code null}, then this package is sealed with
* respect to the given code source {@link java.net.URL URL}
* object. Otherwise, the package is not sealed.
*
* @return The newly defined {@code Package} object
*
* @throws NullPointerException
* if {@code name} is {@code null}.
*
* @throws IllegalArgumentException
* if a package of the given {@code name} is already
* defined by this class loader
*
*
* @since 1.2
* @revised 9
* @spec JPMS
*
* @jvms 5.3 Run-time package
* @see
* The JAR File Specification: Package Sealing
*/
protected Package definePackage(String name, String specTitle,
String specVersion, String specVendor,
String implTitle, String implVersion,
String implVendor, URL sealBase)
{
Objects.requireNonNull(name);
// definePackage is not final and may be overridden by custom class loader
Package p = new Package(name, specTitle, specVersion, specVendor,
implTitle, implVersion, implVendor,
sealBase, this);
if (packages.putIfAbsent(name, p) != null)
throw new IllegalArgumentException(name);
return p;
}
/**
* Returns a {@code Package} of the given name that
* has been defined by this class loader.
*
* @param name The package name
*
* @return The {@code Package} of the given name that has been defined
* by this class loader, or {@code null} if not found
*
* @throws NullPointerException
* if {@code name} is {@code null}.
*
* @jvms 5.3 Run-time package
*
* @since 9
* @spec JPMS
*/
public final Package getDefinedPackage(String name) {
Objects.requireNonNull(name, "name cannot be null");
NamedPackage p = packages.get(name);
if (p == null)
return null;
return definePackage(name, p.module());
}
/**
* Returns all of the {@code Package}s that have been defined by
* this class loader. The returned array has no duplicated {@code Package}s
* of the same name.
*
* @apiNote This method returns an array rather than a {@code Set} or {@code Stream}
* for consistency with the existing {@link #getPackages} method.
*
* @return The array of {@code Package} objects that have been defined by
* this class loader; or an zero length array if no package has been
* defined by this class loader.
*
* @jvms 5.3 Run-time package
*
* @since 9
* @spec JPMS
*/
public final Package[] getDefinedPackages() {
return packages().toArray(Package[]::new);
}
/**
* Finds a package by name in this class loader and its ancestors.
*
* If this class loader defines a {@code Package} of the given name,
* the {@code Package} is returned. Otherwise, the ancestors of
* this class loader are searched recursively (parent by parent)
* for a {@code Package} of the given name.
*
* @apiNote The {@link #getPlatformClassLoader() platform class loader}
* may delegate to the application class loader but the application class
* loader is not its ancestor. When invoked on the platform class loader,
* this method will not find packages defined to the application
* class loader.
*
* @param name
* The package name
*
* @return The {@code Package} of the given name that has been defined by
* this class loader or its ancestors, or {@code null} if not found.
*
* @throws NullPointerException
* if {@code name} is {@code null}.
*
* @deprecated
* If multiple class loaders delegate to each other and define classes
* with the same package name, and one such loader relies on the lookup
* behavior of {@code getPackage} to return a {@code Package} from
* a parent loader, then the properties exposed by the {@code Package}
* may not be as expected in the rest of the program.
* For example, the {@code Package} will only expose annotations from the
* {@code package-info.class} file defined by the parent loader, even if
* annotations exist in a {@code package-info.class} file defined by
* a child loader. A more robust approach is to use the
* {@link ClassLoader#getDefinedPackage} method which returns
* a {@code Package} for the specified class loader.
*
* @see ClassLoader#getDefinedPackage(String)
*
* @since 1.2
* @revised 9
* @spec JPMS
*/
@Deprecated(since="9")
protected Package getPackage(String name) {
Package pkg = getDefinedPackage(name);
if (pkg == null) {
if (parent != null) {
pkg = parent.getPackage(name);
} else {
pkg = BootLoader.getDefinedPackage(name);
}
}
return pkg;
}
/**
* Returns all of the {@code Package}s that have been defined by
* this class loader and its ancestors. The returned array may contain
* more than one {@code Package} object of the same package name, each
* defined by a different class loader in the class loader hierarchy.
*
* @apiNote The {@link #getPlatformClassLoader() platform class loader}
* may delegate to the application class loader. In other words,
* packages in modules defined to the application class loader may be
* visible to the platform class loader. On the other hand,
* the application class loader is not its ancestor and hence
* when invoked on the platform class loader, this method will not
* return any packages defined to the application class loader.
*
* @return The array of {@code Package} objects that have been defined by
* this class loader and its ancestors
*
* @see ClassLoader#getDefinedPackages()
*
* @since 1.2
* @revised 9
* @spec JPMS
*/
protected Package[] getPackages() {
Stream Every native library requires a particular version of JNI. This is
* denoted by the private {@code jniVersion} field. This field is set by
* the VM when it loads the library, and used by the VM to pass the correct
* version of JNI to the native methods. A subpackage of a package named p is any package whose name begins
* with "{@code p.}". For example, {@code javax.swing.text} is a
* subpackage of {@code javax.swing}, and both {@code java.util} and
* {@code java.lang.reflect} are subpackages of {@code java}.
*
* In the event that multiple package defaults apply to a given class,
* the package default pertaining to the most specific package takes
* precedence over the others. For example, if {@code javax.lang} and
* {@code javax.lang.reflect} both have package defaults associated with
* them, the latter package default applies to classes in
* {@code javax.lang.reflect}.
*
* Package defaults take precedence over the class loader's default
* assertion status, and may be overridden on a per-class basis by invoking
* {@link #setClassAssertionStatus(String, boolean)}. If the named class is not a top-level class, this invocation will
* have no effect on the actual assertion status of any class.
*
*
*
*
*
*
* @param module
* The module
* @param name
* The binary name of the class
*
* @return The resulting {@code Class} object in a module defined by
* this class loader, or {@code null} if the class could not be found.
*/
final Class loadClass(Module module, String name) {
synchronized (getClassLoadingLock(name)) {
// First, check if the class has already been loaded
Class c = findLoadedClass(name);
if (c == null) {
c = findClass(module.getName(), name);
}
if (c != null && c.getModule() == module) {
return c;
} else {
return null;
}
}
}
/**
* Returns the lock object for class loading operations.
* For backward compatibility, the default implementation of this method
* behaves as follows. If this ClassLoader object is registered as
* parallel capable, the method returns a dedicated object associated
* with the specified class name. Otherwise, the method returns this
* ClassLoader object.
*
* @param className
* The name of the to-be-loaded class
*
* @return the lock for class loading operations
*
* @throws NullPointerException
* If registered as parallel capable and {@code className} is null
*
* @see #loadClass(String, boolean)
*
* @since 1.7
*/
protected Object getClassLoadingLock(String className) {
Object lock = this;
if (parallelLockMap != null) {
Object newLock = new Object();
lock = parallelLockMap.putIfAbsent(className, newLock);
if (lock == null) {
lock = newLock;
}
}
return lock;
}
// This method is invoked by the virtual machine to load a class.
private Class loadClassInternal(String name)
throws ClassNotFoundException
{
// For backward compatibility, explicitly lock on 'this' when
// the current class loader is not parallel capable.
if (parallelLockMap == null) {
synchronized (this) {
return loadClass(name);
}
} else {
return loadClass(name);
}
}
// Invoked by the VM after loading class with this loader.
private void checkPackageAccess(Class cls, ProtectionDomain pd) {
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
if (ReflectUtil.isNonPublicProxyClass(cls)) {
for (Class intf: cls.getInterfaces()) {
checkPackageAccess(intf, pd);
}
return;
}
final String name = cls.getName();
final int i = name.lastIndexOf('.');
if (i != -1) {
AccessController.doPrivileged(new PrivilegedAction<>() {
public Void run() {
sm.checkPackageAccess(name.substring(0, i));
return null;
}
}, new AccessControlContext(new ProtectionDomain[] {pd}));
}
}
}
/**
* Finds the class with the specified binary name.
* This method should be overridden by class loader implementations that
* follow the delegation model for loading classes, and will be invoked by
* the {@link #loadClass loadClass} method after checking the
* parent class loader for the requested class.
*
* @implSpec The default implementation throws {@code ClassNotFoundException}.
*
* @param name
* The binary name of the class
*
* @return The resulting {@code Class} object
*
* @throws ClassNotFoundException
* If the class could not be found
*
* @since 1.2
*/
protected Class findClass(String name) throws ClassNotFoundException {
throw new ClassNotFoundException(name);
}
/**
* Finds the class with the given binary name
* in a module defined to this class loader.
* Class loader implementations that support the loading from modules
* should override this method.
*
* @apiNote This method returns {@code null} rather than throwing
* {@code ClassNotFoundException} if the class could not be found.
*
* @implSpec The default implementation attempts to find the class by
* invoking {@link #findClass(String)} when the {@code moduleName} is
* {@code null}. It otherwise returns {@code null}.
*
* @param moduleName
* The module name; or {@code null} to find the class in the
* {@linkplain #getUnnamedModule() unnamed module} for this
* class loader
* @param name
* The binary name of the class
*
* @return The resulting {@code Class} object, or {@code null}
* if the class could not be found.
*
* @since 9
* @spec JPMS
*/
protected Class findClass(String moduleName, String name) {
if (moduleName == null) {
try {
return findClass(name);
} catch (ClassNotFoundException ignore) { }
}
return null;
}
/**
* Converts an array of bytes into an instance of class {@code Class}.
* Before the {@code Class} can be used it must be resolved. This method
* is deprecated in favor of the version that takes a binary name as its first argument, and is more secure.
*
* @param b
* The bytes that make up the class data. The bytes in positions
* {@code off} through {@code off+len-1} should have the format
* of a valid class file as defined by
* The Java™ Virtual Machine Specification.
*
* @param off
* The start offset in {@code b} of the class data
*
* @param len
* The length of the class data
*
* @return The {@code Class} object that was created from the specified
* class data
*
* @throws ClassFormatError
* If the data did not contain a valid class
*
* @throws IndexOutOfBoundsException
* If either {@code off} or {@code len} is negative, or if
* {@code off+len} is greater than {@code b.length}.
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class, or if an attempt is made
* to define a class in a package with a fully-qualified name
* that starts with "{@code java.}".
*
* @see #loadClass(String, boolean)
* @see #resolveClass(Class)
*
* @deprecated Replaced by {@link #defineClass(String, byte[], int, int)
* defineClass(String, byte[], int, int)}
*/
@Deprecated(since="1.1")
protected final Class defineClass(byte[] b, int off, int len)
throws ClassFormatError
{
return defineClass(null, b, off, len, null);
}
/**
* Converts an array of bytes into an instance of class {@code Class}.
* Before the {@code Class} can be used it must be resolved.
*
*
* ...
* byte[] temp = new byte[bBuffer.{@link
* java.nio.ByteBuffer#remaining remaining}()];
* bBuffer.{@link java.nio.ByteBuffer#get(byte[])
* get}(temp);
* return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
* cl.defineClass}(name, temp, 0,
* temp.length, pd);
*
*
*