1 /*
2 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util.spi;
27
28 import java.io.PrintStream;
29 import java.io.PrintWriter;
30 import java.util.Objects;
31 import java.util.Optional;
32 import java.util.ServiceLoader;
33
34 /**
35 * An interface for command-line tools to provide a way to
36 * be invoked without necessarily starting a new VM.
37 *
38 * <p>Tool providers are normally located using the service-provider
39 * loading facility defined by {@link ServiceLoader}.
40 * Each provider must provide a name, and a method to run
41 * an instance of the corresponding tool. When a tool is run,
42 * it will be provided with an array of string arguments, and a
43 * pair of streams: one for normal (or expected) output and the other
44 * for reporting any errors that may occur.
45 * The interpretation of the string arguments will normally be defined by
46 * each individual tool provider, but will generally correspond to the
47 * arguments that could be provided to the tool when invoking the tool
48 * from the command line.
49 *
50 * @since 9
51 */
52 public interface ToolProvider {
53 /**
54 * Returns the name of this tool provider.
55 * @apiNote It is recommended that the name be the same as would
56 * be used on the command line: for example, "javac", "jar", "jlink".
57 * @return the name of this tool provider
58 */
59 String name();
60
61 /**
62 * Runs an instance of the tool, returning zero for a successful run.
63 * Any nonzero return value indicates a tool-specific error during the
64 * execution.
65 * Two streams should be provided, for "expected" output, and for any
66 * error messages. If it is not necessary to distinguish the output,
67 * the same stream may be used for both.
68 * @apiNote The interpretation of the arguments will be specific to
69 * each tool.
70 * @param out a stream to which "expected" output should be written
71 * @param err a stream to which any error messages should be written
72 * @param args the command-line arguments for the tool
73 * @return the result of executing the tool.
74 * A return value of 0 means the tool did not encounter any errors;
75 * any other value indicates that at least one error occurred during
76 * execution.
77 * @throws NullPointerException if any of the arguments are {@code null},
78 * or if there are any {@code null} values in the {@code args} array
79 */
80 int run(PrintWriter out, PrintWriter err, String... args);
81
82 /**
83 * Runs an instance of the tool, returning zero for a successful run.
84 * Any non-zero return value indicates a tool-specific error during the
85 * execution.
86 * Two streams should be provided, for "expected" output, and for any
87 * error messages. If it is not necessary to distinguish the output,
88 * the same stream may be used for both.
89 * @apiNote The interpretation of the arguments will be specific to
90 * each tool.
91 * @implNote This implementation wraps the {@code out} and {@code err}
92 * streams within {@link PrintWriter}s, and then calls
93 * {@link run(PrintWriter, PrintWriter, String[])}.
94 * @param out a stream to which "expected" output should be written
95 * @param err a stream to which any error messages should be written
96 * @param args the command-line arguments for the tool
97 * @return the result of executing the tool.
98 * A return value of 0 means the tool did not encounter any errors;
99 * any other value indicates that at least one error occurred during
100 * execution.
101 * @throws NullPointerException if any of the arguments are {@code null},
102 * or if there are any {@code null} values in the {@code args} array
103 */
104 default int run(PrintStream out, PrintStream err, String... args) {
105 Objects.requireNonNull(out);
106 Objects.requireNonNull(err);
107 for (String arg : args) {
108 Objects.requireNonNull(args);
109 }
110
111 PrintWriter outWriter = new PrintWriter(out);
112 PrintWriter errWriter = new PrintWriter(err);
113 try {
114 try {
115 return run(outWriter, errWriter, args);
116 } finally {
117 outWriter.flush();
118 }
119 } finally {
120 errWriter.flush();
121 }
122 }
123
124 /**
125 * Returns the first instance of a {@code ToolProvider} with the given name,
126 * as loaded by {@link ServiceLoader} using the system class loader.
127 * @param name the name of the desired tool provider
128 * @return an {@code Optional<ToolProvider>} of the first instance found
129 * @throws NullPointerException if {@code name} is {@code null}
130 */
131 static Optional<ToolProvider> findFirst(String name) {
132 Objects.requireNonNull(name);
133 for (ToolProvider p : ServiceLoader.load(ToolProvider.class,
134 ClassLoader.getSystemClassLoader())) {
135 if (p.name().equals(name)) {
136 return Optional.of(p);
137 }
138 }
139 return Optional.empty();
140 }
141 }
142