动态加载java代码

	public String compile(String srcFiles[]) {
		//StringWriter err = new StringWriter();
		//PrintWriter errPrinter = new PrintWriter(err);
		ByteArrayOutputStream err=new ByteArrayOutputStream();
		

		String args[] = buildJavacArgs(srcFiles);
		//int resultCode = com.sun.tools.javac.Main.compile(args, errPrinter);
		logger.warn("Dyna Complie Java Source:---->"+args);						
		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
		if(compiler==null){
			throw new NullPointerException("ToolProvider.getSystemJavaCompiler() return null,please use JDK replace JRE!");
		}
		int resultCode = compiler.run(null, null, err, args);
		
		return (resultCode == 0) ? null : err.toString();
	}

参数设置正确了

private String[] buildJavacArgs(String srcFiles[]) {
		ArrayList args = new ArrayList();

		if (classpath != null) {
			args.add("-classpath");
			args.add(classpath);
		}
		if (outputdir != null) {
			args.add("-d");
			args.add(outputdir);
		}
		if (sourcepath != null) {
			args.add("-sourcepath");
			args.add(sourcepath);
		}
		if (bootclasspath != null) {
			args.add("-bootclasspath");
			args.add(bootclasspath);
		}
		if (extdirs != null) {
			args.add("-extdirs");
			args.add(extdirs);
		}
		if (encoding != null) {
			args.add("-encoding");
			args.add(encoding);
		}
		if (target != null) {
			args.add("-target");
			args.add(target);
		}

		for (int i = 0; i < srcFiles.length; i++) {
			args.add(srcFiles[i]);
		}

		return (String[]) args.toArray(new String[args.size()]);
	}

/**
	 * Extracts a classpath string from a given class loader. Recognizes only
	 * URLClassLoader.
	 */
	private static String extractClasspath(ClassLoader cl) {
		StringBuffer buf = new StringBuffer();

		while (cl != null) {
			if (cl instanceof URLClassLoader) {
				URL urls[] = ((URLClassLoader) cl).getURLs();

				for (int i = 0; i < urls.length; i++) {
					if (buf.length() > 0) {
						buf.append(File.pathSeparatorChar);
					}
					String s = urls[i].getFile();

					try {
						s = URLDecoder.decode(s, "UTF-8");
					} catch (UnsupportedEncodingException e) {
						continue;
					}
					File f = new File(s);

					// f.isFile()
					buf.append(f.getAbsolutePath());
				}
			}
			cl = cl.getParent();
		}
		return buf.toString();
	}

创建load上述class的ClassLoader时，指定的load class的路径要和上面编译的输出路径一致

classLoader = new URLClassLoader(new URL[] { binDir.toURL() },
						parentClassLoader);

后面就可以用特定的ClassLoader来加载class文件了，再后面就可以newInstance了。