Java版的实现JavaScript中的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;

/**
* Description:
* <br/>网站: <a href="http://www.crazyit.org" mce_href="http://www.crazyit.org">疯狂Java联盟</a>
* <br/>Copyright (C), 2001-2010, Leeyohn
* <br/>This program is protected by copyright laws.
* <br/>Program Name:
* <br/>Date:
* @author Leeyohn [email protected]
* @version 1.0
*/

public class MyClassLoader
extends ClassLoader
{
@Override
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;

/**
* Description:
* <br/>网站: <a href="http://www.crazyit.org" mce_href="http://www.crazyit.org">疯狂Java联盟</a>
* <br/>Copyright (C), 2001-2010, Leeyohn
* <br/>This program is protected by copyright laws.
* <br/>Program Name:
* <br/>Date:
* @author Leeyohn [email protected]
* @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);
}
}