java怎么调用js代码_在Java中直接调用js代码

JDK1.6版添加了新的ScriptEngine类&＃xff0c;允许用户直接执行js代码。

在Java中直接调用js代码

不能调用浏览器中定义的js函数&＃xff0c;会抛出异常提示ReferenceError: “alert” is not defined。

package com.sinaapp.manjushri;

import javax.script.ScriptEngine;

import javax.script.ScriptEngineManager;

import javax.script.ScriptException;

/**

* 直接调用js代码

* */

public class ScriptEngineTest {

public static void main(String[] args) {

ScriptEngineManager manager &＃61; new ScriptEngineManager();

ScriptEngine engine &＃61; manager.getEngineByName("Javascript");

try{

engine.eval("var a&＃61;3; var b&＃61;4;print (a&＃43;b);");

// engine.eval("alert(\"js alert\");"); // 不能调用浏览器中定义的js函数&＃xff0c;会抛出alert引用不存在的异常

}catch(ScriptException e){

e.printStackTrace();

}

}

}

输出结果&＃xff1a;7

在Java中绑定js变量

在调用engine.get(key);时&＃xff0c;如果key没有定义&＃xff0c;则返回null

package com.sinaapp.manjushri;

import javax.script.Bindings;

import javax.script.ScriptContext;

import javax.script.ScriptEngine;

import javax.script.ScriptEngineManager;

import javax.script.ScriptException;

public class ScriptEngineTest2 {

public static void main(String[] args) {

ScriptEngineManager manager &＃61; new ScriptEngineManager();

ScriptEngine engine &＃61; manager.getEngineByName("Javascript");

engine.put("a", 4);

engine.put("b", 3);

Bindings bindings &＃61; engine.getBindings(ScriptContext.ENGINE_SCOPE);

try {

// 只能为Double&＃xff0c;使用Float和Integer会抛出异常

Double result &＃61; (Double) engine.eval("a&＃43;b");

System.out.println("result &＃61; " &＃43; result);

engine.eval("c&＃61;a&＃43;b");

Double c &＃61; (Double)engine.get("c");

System.out.println("c &＃61; " &＃43; c);

} catch (ScriptException e) {

e.printStackTrace();

}

}

}

输出&＃xff1a;

result &＃61; 7.0

c &＃61; 7.0

在Java中调用js文件中的function&＃xff0c;传入调用参数&＃xff0c;并获取返回值

js文件中的merge函数将两个参数a&＃xff0c;b相加&＃xff0c;返回结果

// expression.js

function merge(a, b) {

return a &＃43; b;

}

在Java代码中读取js文件&＃xff0c;传入两个参数&＃xff0c;获得返回值。

package com.sinaapp.manjushri;

import java.io.FileReader;

import javax.script.Invocable;

import javax.script.ScriptEngine;

import javax.script.ScriptEngineManager;

/**

* Java调用并执行js文件&＃xff0c;传递参数&＃xff0c;并活动返回值

**/

public class ScriptEngineTest {

public static void main(String[] args) throws Exception {

ScriptEngineManager manager &＃61; new ScriptEngineManager();

ScriptEngine engine &＃61; manager.getEngineByName("Javascript");

String jsFileName &＃61; "expression.js"; // 读取js文件

FileReader reader &＃61; new FileReader(jsFileName); // 执行指定脚本

engine.eval(reader);

if(engine instanceof Invocable) {

Invocable invoke &＃61; (Invocable)engine;

// 调用merge方法&＃xff0c;并传入两个参数

Double c &＃61; (Double)invoke.invokeFunction("merge", 2, 3);

System.out.println("c &＃61; " &＃43; c);

}

reader.close();

}

}

输出结果&＃xff1a;

c &＃61; 5.0