未找到JavaCompiler編譯類

Question

我已經使用JavaCompiler來編譯我在運行中生成的類。編譯任務成功。然後我嘗試使用Class.forName("MyClass")加載編譯的類;並且它以ClassNotFoundException失敗。這樣做有沒有已知的問題？

package com.amir.method; 

import java.io.*; 
import java.lang.reflect.Method; 
import java.net.URI; 
import java.net.URL; 
import java.net.URLClassLoader; 
import java.util.ArrayList; 
import java.util.Arrays; 
import java.util.List; 
import java.util.Set; 

import javax.tools.*; 

public class MethodGenerator { 

    private final static MethodGenerator INSTANCE = new MethodGenerator(); 

    private MethodGenerator() { 
    } 

    public static MethodGenerator get() { 
     return INSTANCE; 
    } 


    public static void main(String[] args) { 

     final Class<?> clz = MethodGenerator.get().compile("Foo", "doIt"); //<- args ignored for now 

    } 

    public Class compile(final String className, 
         final String methodName) { 
     try { 
      return doCompile(className, methodName); 
     } catch(final Exception e) { 
      throw new RuntimeException(this.toString(), e); 
     } 

    } 

    private Class doCompile(final String className, 
          final String methodName) throws IOException, ClassNotFoundException { 

     JavaCompiler compiler = ToolProvider.getSystemJavaCompiler(); 
     DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>(); 

     StringWriter writer = new StringWriter(); 
     PrintWriter out = new PrintWriter(writer); 
     out.println("public class HelloWorld {"); 
     out.println(" public static void main(String args[]) {"); 
     out.println(" System.out.println(\"This is in another java file\");"); 
     out.println(" }"); 
     out.println("}"); 
     out.close(); 

     final JavaFileObject file = new JavaSourceFromString("HelloWorld", writer.toString()); 
     final Iterable<? extends JavaFileObject> compilationUnits = Arrays.asList(file); 
     final String classPath = System.getProperty("java.class.path") + File.pathSeparator; 
     final String bootClassPath = System.getProperty("sun.boot.class.path") + File.pathSeparator; 
     final List<String> options = new ArrayList<String>(); 
     options.add("-classpath"); 
     final StringBuilder builder = new StringBuilder(); 
     builder.append(classPath); 
     builder.append(bootClassPath); 
     final URLClassLoader urlClassLoader = (URLClassLoader) ClassLoaderResolver.getClassLoader(); 
     for (final URL url : urlClassLoader.getURLs()) { 
      builder.append(url.getFile()).append(File.pathSeparator); 
     } 
     final int lastIndexOfColon = builder.lastIndexOf(File.pathSeparator); 
     builder.replace(lastIndexOfColon, lastIndexOfColon + 1, ""); 
     options.add(builder.toString()); 

     final JavaCompiler.CompilationTask task = compiler.getTask(null, null, diagnostics, options, null, compilationUnits); 

     boolean success = task.call(); 

     if(success) { 
      final Class<?> cls = Class.forName("HelloWorld", true, urlClassLoader); 
      return cls; 
     } 

     return null; 

    } 

    class JavaSourceFromString extends SimpleJavaFileObject { 
     final String code; 

     JavaSourceFromString(String name, String code) { 
      super(URI.create("string:///" + name.replace('.', '/') + Kind.SOURCE.extension),Kind.SOURCE); 
      this.code = code; 
     } 

     @Override 
     public CharSequence getCharContent(boolean ignoreEncodingErrors) { 
      return code; 
     } 
    } 

} 

Answer 1

嘗試通過編譯之後加載類，Thread.currentThread().getContextClassLoader().loadClass("com.ur.class");

發現這個...檢查是否這可以幫助..

// Create a new custom class loader, pointing to the directory that contains the compiled 
// classes, this should point to the top of the package structure! 
URLClassLoader classLoader = new URLClassLoader(new URL[]{new File("./").toURI().toURL()}); 
// Load the class from the classloader by name.... 
Class<?> loadedClass = classLoader.loadClass("com.ur.class"); 
// Create a new instance... 
Object obj = loadedClass.newInstance(); 
// Santity check 
if (obj instanceof com.ur.class) { 
    // code here ... 
} 

欲瞭解更多信息，請參閱本：How do you dynamically compile and load external java classes?