如何将 JDK6 ToolProvider 和 JavaCompiler 与上下文类加载器一起使用？

发布于 2024-07-08 06:04:16 字数 909 浏览 8 评论 0原文

我的用例是使用 JDK 6 中提供的 ToolProvider 和 JavaCompiler 类从 java 程序编译生成的源文件。源文件包含对上下文类加载器（它在 J2EE 容器中运行）中的类的引用，但不包含对系统类加载器中的类的引用。我的理解是，默认情况下 ToolProvider 将使用系统类加载器创建 JavaCompiler 实例。

有没有办法指定JavaCompiler使用的类加载器？

我尝试了这种方法，修改自 IBM DeveloperWorks 上的某些内容：

FileManagerImpl fm = 
    new FileManagerImpl(compiler.getStandardFileManager(null, null, null););

FileManagerImpl 定义为：

static final class FileManagerImpl 
    extends ForwardingJavaFileManager<JavaFileManager> {

   public FileManagerImpl(JavaFileManager fileManager) {
      super(fileManager);
   }

   @Override
   public ClassLoader getClassLoader(JavaFileManager.Location location) {
      new Exception().printStackTrace();
      return Thread.currentThread().getContextClassLoader();
   }

}

堆栈跟踪表明它在注释处理期间仅调用一次。我验证了要编译的源文件中引用的类不在系统类路径上，但可以从上下文类加载器中获取。

原文

My usage case is compiling generated source files from a java program using the ToolProvider and JavaCompiler classes provided in JDK 6. The source files contain references to classes in the context classloader (it runs in a J2EE container), but not in the system classloader. My understanding is that by default the ToolProvider will create the JavaCompiler instance with the system classloader.

Is there a way to specify a classloader for JavaCompiler to use?

I tried this approach, modified from something on IBM DeveloperWorks:

FileManagerImpl fm = 
    new FileManagerImpl(compiler.getStandardFileManager(null, null, null););

with FileManagerImpl defined as:

static final class FileManagerImpl 
    extends ForwardingJavaFileManager<JavaFileManager> {

   public FileManagerImpl(JavaFileManager fileManager) {
      super(fileManager);
   }

   @Override
   public ClassLoader getClassLoader(JavaFileManager.Location location) {
      new Exception().printStackTrace();
      return Thread.currentThread().getContextClassLoader();
   }

}

The stacktrace indicates it's only called once during annotation processing. I verified the class referenced in the source file to be compiled is not on the system classpath but is available from the context classloader.

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仙女山的月亮 2024-07-15 06:04:16

如果您知道 contextclassloader 已知的文件的类路径，则可以将它们传递给编译器：

    StandardJavaFileManager fileManager = compiler.getStandardFileManager(this /* diagnosticlistener */, null, null);
// get compilationunits from somewhere, for instance via fileManager.getJavaFileObjectsFromFiles(List<file> files)
List<String> options = new ArrayList<String>();
options.add("-classpath");
StringBuilder sb = new StringBuilder();
URLClassLoader urlClassLoader = (URLClassLoader) Thread.currentThread().getContextClassLoader();
for (URL url : urlClassLoader.getURLs())
    sb.append(url.getFile()).append(File.pathSeparator);
options.add(sb.toString());
CompilationTask task = compiler.getTask(null, fileManager, this /* diagnosticlistener */, options, null, compilationUnits);
task.call();

此示例假设您正在使用 URLClassloader（它允许您检索类路径），但如果需要，您可以插入自己的类路径到。

If you know the classpath to the files that are known to the contextclassloader you can pass them to the compiler:

    StandardJavaFileManager fileManager = compiler.getStandardFileManager(this /* diagnosticlistener */, null, null);
// get compilationunits from somewhere, for instance via fileManager.getJavaFileObjectsFromFiles(List<file> files)
List<String> options = new ArrayList<String>();
options.add("-classpath");
StringBuilder sb = new StringBuilder();
URLClassLoader urlClassLoader = (URLClassLoader) Thread.currentThread().getContextClassLoader();
for (URL url : urlClassLoader.getURLs())
    sb.append(url.getFile()).append(File.pathSeparator);
options.add(sb.toString());
CompilationTask task = compiler.getTask(null, fileManager, this /* diagnosticlistener */, options, null, compilationUnits);
task.call();

This example assumes you're using a URLClassloader (which allows you to retrieve the classpath) but you could insert your own classpath if you wanted to.

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