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.security.AccessController;
31 import java.security.PrivilegedAction;
32 import java.util.Objects;
33 import java.util.Optional;
34 import java.util.ServiceLoader;
35 import java.util.stream.StreamSupport;
36
37 /**
38 * An interface for command-line tools to provide a way to
39 * be invoked without necessarily starting a new VM.
40 *
41 * <p>Tool providers are normally located using the service-provider
42 * loading facility defined by {@link ServiceLoader}.
43 * Each provider must provide a name, and a method to run
44 * an instance of the corresponding tool. When a tool is run,
45 * it will be provided with an array of string arguments, and a
46 * pair of streams: one for normal (or expected) output and the other
47 * for reporting any errors that may occur.
48 * The interpretation of the string arguments will normally be defined by
49 * each individual tool provider, but will generally correspond to the
50 * arguments that could be provided to the tool when invoking the tool
51 * from the command line.
52 *
53 * @since 9
54 */
55 public interface ToolProvider {
56 /**
57 * Returns the name of this tool provider.
58 *
59 * @apiNote It is recommended that the name be the same as would be used on
60 * the command line: for example, "javac", "jar", "jlink".
61 *
62 * @return the name of this tool provider
63 */
64 String name();
65
66 /**
67 * Runs an instance of the tool, returning zero for a successful run.
68 * Any non-zero return value indicates a tool-specific error during the
69 * execution.
70 * Two streams should be provided, for "expected" output, and for any
71 * error messages. If it is not necessary to distinguish the output,
72 * the same stream may be used for both.
73 *
74 * @apiNote The interpretation of the arguments will be specific to
75 * each tool.
76 *
77 * @param out a stream to which "expected" output should be written
78 *
79 * @param err a stream to which any error messages should be written
80 *
81 * @param args the command-line arguments for the tool
82 *
83 * @return the result of executing the tool.
84 * A return value of 0 means the tool did not encounter any errors;
85 * any other value indicates that at least one error occurred during
86 * execution.
87 *
88 * @throws NullPointerException if any of the arguments are {@code null},
89 * or if there are any {@code null} values in the {@code args} array
90 */
91 int run(PrintWriter out, PrintWriter err, String... args);
92
93 /**
94 * Runs an instance of the tool, returning zero for a successful run.
95 * Any non-zero return value indicates a tool-specific error during the
96 * execution.
97 * Two streams should be provided, for "expected" output, and for any
98 * error messages. If it is not necessary to distinguish the output,
99 * the same stream may be used for both.
100 *
101 * @apiNote The interpretation of the arguments will be specific to
102 * each tool.
103 *
104 * @implNote This implementation wraps the {@code out} and {@code err}
105 * streams within {@link PrintWriter}s, and then calls
106 * {@link run(PrintWriter, PrintWriter, String[])}.
107 *
108 * @param out a stream to which "expected" output should be written
109 *
110 * @param err a stream to which any error messages should be written
111 *
112 * @param args the command-line arguments for the tool
113 *
114 * @return the result of executing the tool.
115 * A return value of 0 means the tool did not encounter any errors;
116 * any other value indicates that at least one error occurred during
117 * execution.
118 *
119 * @throws NullPointerException if any of the arguments are {@code null},
120 * or if there are any {@code null} values in the {@code args} array
121 */
122 default int run(PrintStream out, PrintStream err, String... args) {
123 Objects.requireNonNull(out);
124 Objects.requireNonNull(err);
125 for (String arg : args) {
126 Objects.requireNonNull(args);
127 }
128
129 PrintWriter outWriter = new PrintWriter(out);
130 PrintWriter errWriter = new PrintWriter(err);
131 try {
132 try {
133 return run(outWriter, errWriter, args);
134 } finally {
135 outWriter.flush();
136 }
137 } finally {
138 errWriter.flush();
139 }
140 }
141
142 /**
143 * Returns the first instance of a {@code ToolProvider} with the given name,
144 * as loaded by {@link ServiceLoader} using the system class loader.
145 *
146 * @param name the name of the desired tool provider
147 *
148 * @return an {@code Optional<ToolProvider>} of the first instance found
149 *
150 * @throws NullPointerException if {@code name} is {@code null}
151 */
152 static Optional<ToolProvider> findFirst(String name) {
153 Objects.requireNonNull(name);
154 ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
155 return AccessController.doPrivileged(
156 (PrivilegedAction<Optional<ToolProvider>>) () -> {
157 ServiceLoader<ToolProvider> sl =
158 ServiceLoader.load(ToolProvider.class, systemClassLoader);
159 return StreamSupport.stream(sl.spliterator(), false)
160 .filter(p -> p.name().equals(name))
161 .findFirst();
162 });
163 }
164 }
165