java 实现 javascript eval 函数

import java.util.Arrays;
import javax.tools.SimpleJavaFileObject;
import javax.tools.JavaFileObject;
import javax.tools.JavaCompiler;
import javax.tools.ToolProvider;
import javax.tools.DiagnosticCollector;
import java.net.URI;



 * @version  1.0
 */

public class 
    extends ClassLoader
{
    
    public Class<?> findClass(String str) throws ClassNotFoundException
    {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        //用于诊断源代码编译错误的对象
        DiagnosticCollector diagnostics = new DiagnosticCollector();
        //内存中的源代码保存在一个从JavaFileObject继承的类中 
        JavaFileObject file = new JavaSourceFromString("Temp", str.toString());
        Iterable compilationUnits = Arrays.asList(file);
        //建立一个编译任务
        JavaCompiler.CompilationTask task = compiler.getTask(null, null, null, null, null, compilationUnits);
        //编译源程序
        boolean result = task.call();
        if (result) 
        {
            return Class.forName("Temp");
        }
        return null;
    }
}

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

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

 import java.lang.reflect.Method;  
  
/** 
 * @version  1.0 
 */  
  
public class Eval   
{  
    public static Object eval(String str) throws Exception  
    {  
        StringBuffer sb = new StringBuffer();  
        sb.append("public class Temp");  
        sb.append("{");  
        sb.append("    public Object getObject()");  
        sb.append("    {");  
        sb.append("        " + str + "return new Object();");  
        sb.append("    }");  
        sb.append("}");  
        //调用自定义类加载器加载编译在内存中class文件  
        Class clazz = new MyClassLoader().findClass(sb.toString());  
        Method method = clazz.getMethod("getObject");  
        //通过反射调用方法  
        return method.invoke(clazz.newInstance());  
    }  
  
    public static void main(String[] args) throws Exception  
    {  
        Object rval = eval("System.out.println(/"Hello World/");");  
        System.out.println(rval);  
    }  
}