ToolProvider.java revision 3474:dcb234002184 
1/*
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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
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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
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24 */
25
26package javax.tools;
27
28import java.lang.reflect.InvocationTargetException;
29import java.lang.reflect.Method;
30import java.security.AccessController;
31import java.security.PrivilegedAction;
32import java.util.Iterator;
33import java.util.ServiceConfigurationError;
34import java.util.ServiceLoader;
35
36/**
37 * Provides methods for locating tool providers, for example,
38 * providers of compilers.  This class complements the
39 * functionality of {@link java.util.ServiceLoader}.
40 *
41 * @author Peter von der Ahé
42 * @since 1.6
43 */
44public class ToolProvider {
45
46    private static final String systemJavaCompilerModule = "jdk.compiler";
47    private static final String systemJavaCompilerName   = "com.sun.tools.javac.api.JavacTool";
48
49    /**
50     * Returns the Java™ programming language compiler provided
51     * with this platform.
52     * <p>The file manager returned by calling
53     * {@link JavaCompiler#getStandardFileManager getStandardFileManager}
54     * on this compiler supports paths provided by any
55     * {@linkplain java.nio.file.FileSystem filesystem}.</p>
56     * @return the compiler provided with this platform or
57     * {@code null} if no compiler is provided
58     * @implNote This implementation returns the compiler provided
59     * by the {@code jdk.compiler} module if that module is available,
60     * and null otherwise.
61     */
62    public static JavaCompiler getSystemJavaCompiler() {
63        return getSystemTool(JavaCompiler.class,
64                systemJavaCompilerModule, systemJavaCompilerName);
65    }
66
67    private static final String systemDocumentationToolModule = "jdk.javadoc";
68    private static final String systemDocumentationToolName = "jdk.javadoc.internal.api.JavadocTool";
69
70    /**
71     * Returns the Java&trade; programming language documentation tool provided
72     * with this platform.
73     * <p>The file manager returned by calling
74     * {@link DocumentationTool#getStandardFileManager getStandardFileManager}
75     * on this tool supports paths provided by any
76     * {@linkplain java.nio.file.FileSystem filesystem}.</p>
77     * @return the documentation tool provided with this platform or
78     * {@code null} if no documentation tool is provided
79     * @implNote This implementation returns the tool provided
80     * by the {@code jdk.javadoc} module if that module is available,
81     * and null otherwise.
82     */
83    public static DocumentationTool getSystemDocumentationTool() {
84        return getSystemTool(DocumentationTool.class,
85                systemDocumentationToolModule, systemDocumentationToolName);
86    }
87
88    /**
89     * Returns the class loader for tools provided with this platform.
90     * This does not include user-installed tools.  Use the
91     * {@linkplain java.util.ServiceLoader service provider mechanism}
92     * for locating user installed tools.
93     *
94     * @return the class loader for tools provided with this platform
95     * or {@code null} if no tools are provided
96     */
97    public static ClassLoader getSystemToolClassLoader() {
98        return ClassLoader.getSystemClassLoader();
99    }
100
101    private static final boolean useLegacy;
102
103    static {
104        Class<?> c = null;
105        try {
106            c = Class.forName("java.lang.reflect.Module");
107        } catch (Throwable t) {
108        }
109        useLegacy = (c == null);
110    }
111
112    /**
113     * Get an instance of a system tool using the service loader.
114     * @implNote         By default, this returns the implementation in the specified module.
115     *                   For limited backward compatibility, if this code is run on an older version
116     *                   of the Java platform that does not support modules, this method will
117     *                   try and create an instance of the named class. Note that implies the
118     *                   class must be available on the system class path.
119     * @param <T>        the interface of the tool
120     * @param clazz      the interface of the tool
121     * @param moduleName the name of the module containing the desired implementation
122     * @param className  the class name of the desired implementation
123     * @return the specified implementation of the tool
124     */
125    private static <T> T getSystemTool(Class<T> clazz, String moduleName, String className) {
126        if (useLegacy) {
127            try {
128                return Class.forName(className, true, ClassLoader.getSystemClassLoader()).
129                    asSubclass(clazz).getConstructor().newInstance();
130            } catch (ReflectiveOperationException e) {
131                throw new Error(e);
132            }
133        }
134
135        try {
136            ServiceLoader<T> sl = ServiceLoader.load(clazz, ClassLoader.getSystemClassLoader());
137            for (Iterator<T> iter = sl.iterator(); iter.hasNext(); ) {
138                T tool = iter.next();
139                if (matches(tool, moduleName))
140                    return tool;
141            }
142        } catch (ServiceConfigurationError e) {
143            throw new Error(e);
144        }
145        return null;
146    }
147
148    /**
149     * Determine if this is the desired tool instance.
150     * @param <T>        the interface of the tool
151     * @param tool       the instance of the tool
152     * @param moduleName the name of the module containing the desired implementation
153     * @return true if and only if the tool matches the specified criteria
154     */
155    private static <T> boolean matches(T tool, String moduleName) {
156        PrivilegedAction<Boolean> pa = () -> {
157            // for now, use reflection to implement
158            //      return moduleName.equals(tool.getClass().getModule().getName());
159            try {
160                Method getModuleMethod = Class.class.getDeclaredMethod("getModule");
161                Object toolModule = getModuleMethod.invoke(tool.getClass());
162                Method getNameMethod = toolModule.getClass().getDeclaredMethod("getName");
163                String toolModuleName = (String) getNameMethod.invoke(toolModule);
164                return moduleName.equals(toolModuleName);
165            } catch (InvocationTargetException | NoSuchMethodException | IllegalAccessException e) {
166                return false;
167            }
168        };
169        return AccessController.doPrivileged(pa);
170    }
171}
172