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25 
26 package javax.tools;
27 
28 import java.security.AccessController;
29 import java.security.PrivilegedAction;
30 import java.util.Objects;
31 import java.util.ServiceConfigurationError;
32 import java.util.ServiceLoader;
33 
34 /**
35  * Provides methods for locating tool providers, for example,
36  * providers of compilers.  This class complements the
37  * functionality of {@link java.util.ServiceLoader}.
38  *
39  * @author Peter von der Ahé
40  * @since 1.6
41  */
42 public class ToolProvider {
43 
44     private static final String systemJavaCompilerModule = "jdk.compiler";
45     private static final String systemJavaCompilerName   = "com.sun.tools.javac.api.JavacTool";
46 
ToolProvider()47     private ToolProvider() {}
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 {@code null} otherwise.
61      */
getSystemJavaCompiler()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 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 {@code null} otherwise.
82      */
getSystemDocumentationTool()83     public static DocumentationTool getSystemDocumentationTool() {
84         return getSystemTool(DocumentationTool.class,
85                 systemDocumentationToolModule, systemDocumentationToolName);
86     }
87 
88     /**
89      * Returns a class loader that may be used to load system tools,
90      * or {@code null} if no such special loader is provided.
91      * @implSpec This implementation always returns {@code null}.
92      * @deprecated This method is subject to removal in a future version of
93      * Java SE.
94      * Use the {@link java.util.spi.ToolProvider system tool provider} or
95      * {@link java.util.ServiceLoader service loader} mechanisms to
96      * locate system tools as well as user-installed tools.
97      * @return a class loader, or {@code null}
98      */
99     @Deprecated(since="9")
getSystemToolClassLoader()100     public static ClassLoader getSystemToolClassLoader() {
101         return null;
102     }
103 
104     /**
105      * Get an instance of a system tool using the service loader.
106      * @implNote         By default, this returns the implementation in the specified module.
107      *                   For limited backward compatibility, if this code is run on an older version
108      *                   of the Java platform that does not support modules, this method will
109      *                   try and create an instance of the named class. Note that implies the
110      *                   class must be available on the system class path.
111      * @param <T>        the interface of the tool
112      * @param clazz      the interface of the tool
113      * @param moduleName the name of the module containing the desired implementation
114      * @param className  the class name of the desired implementation
115      * @return the specified implementation of the tool
116      */
getSystemTool(Class<T> clazz, String moduleName, String className)117     private static <T> T getSystemTool(Class<T> clazz, String moduleName, String className) {
118 
119         try {
120             ServiceLoader<T> sl = ServiceLoader.load(clazz, ClassLoader.getSystemClassLoader());
121             for (T tool : sl) {
122                 if (matches(tool, moduleName))
123                     return tool;
124             }
125         } catch (ServiceConfigurationError e) {
126             throw new Error(e);
127         }
128         return null;
129     }
130 
131     /**
132      * Determine if this is the desired tool instance.
133      * @param <T>               the interface of the tool
134      * @param tool              the instance of the tool
135      * @param moduleName        the name of the module containing the desired implementation
136      * @return true if and only if the tool matches the specified criteria
137      */
matches(T tool, String moduleName)138     private static <T> boolean matches(T tool, String moduleName) {
139         PrivilegedAction<Boolean> pa = () -> {
140             Module toolModule = tool.getClass().getModule();
141             String toolModuleName = toolModule.getName();
142             return Objects.equals(toolModuleName, moduleName);
143         };
144         return AccessController.doPrivileged(pa);
145     }
146 }
147