在Java中直接调用js代码

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 = new ScriptEngineManager();
  ScriptEngine engine = manager.getEngineByName("javascript");
     try{    

          engine.eval("var a=3; var b=4;print (a+b);");

         // engine.eval("alert(\"js alert\");");    // 不能调用浏览器中定义的js函数 // 错误，会抛出alert引用不存在的异常
 }catch(ScriptException e){

 e.printStackTrace();
 }
 }   
}

输出结果：7

在Java中绑定js变量
在调用engine.get(key);时，如果key没有定义，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 = new ScriptEngineManager();   
ScriptEngine engine = manager.getEngineByName("javascript");   
engine.put("a", 4);   
engine.put("b", 3);   
Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);  
try {                        
 // 只能为Double，使用Float和Integer会抛出异常    

Double result = (Double) engine.eval("a+b");       

System.out.println("result = " + result);    
engine.eval("c=a+b");    

Double c = (Double)engine.get("c");    

System.out.println("c = " + c);   

    } catch (ScriptException e) { 
   e.printStackTrace();   

    }  

  } 

}

输出：
result = 7.0
c = 7.0

在Java中调用js文件中的function，传入调用参数，并获取返回值

// expression.js 
function merge(a, b) { 
 c = a * b; 
 return c; 
}

在Java代码中读取js文件，并参数两个参数，然后回去返回值。

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，传递参数，并活动返回值  *   * @author manjushri  */ 

public class ScriptEngineTest {    

public static void main(String[] args) throws Exception {   
ScriptEngineManager manager = new ScriptEngineManager();   
ScriptEngine engine = manager.getEngineByName("javascript");     

String jsFileName = "expression.js";   // 读取js文件   

FileReader reader = new FileReader(jsFileName);   // 执行指定脚本   
engine.eval(reader);   

if(engine instanceof Invocable) {    
Invocable invoke = (Invocable)engine;    // 调用merge方法，并传入两个参数    

// c = merge(2, 3);    

Double c = (Double)invoke.invokeFunction("merge", 2, 3);    

System.out.println("c = " + c);   
}   

reader.close();  

  }
}

原文参考：
https://blog.csdn.net/z834410038/article/details/70231544