Java和Js之間的調用、java8新特性：ScriptEngineManager

## Java和Js之間的調用時基於ScriptEngineManager類，這個類是jdk8新增的

/**
 * @Author Evan
 * @Description //TODO Java和Js之間的調用時基於ScriptEngineManager類，這個類是jdk8新增的
 * @Date 9:45 2019/10/14
 * @Param 
 * @return 
 **/
public class JavaScriptFunction {

    @Test
    public void print() throws Exception {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("JavaScript");
        engine.eval("print('hello word!!')");
    }

    @Test
    public void obj() throws Exception {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("JavaScript");
        StringBuffer script = new StringBuffer();
        script.append("var obj = new Object();");
        script.append("obj.hello = function(name){print('hello, '+name);}");
        //執行這段script腳本
        engine.eval(script.toString());
        // javax.script.Invocable 是一個可選的接口
        // 檢查你的script engine 接口是否已實現!
        // 注意：JavaScript engine實現了Invocable接口
        Invocable inv = (Invocable) engine;
        // 獲取我們想調用那個方法所屬的js對象
        Object obj = engine.get("obj");
        // 執行obj對象的名爲hello的方法
        inv.invokeMethod(obj, "hello", "Script Method !!");
    }

    @Test
    public void file() throws Exception {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("JavaScript");
        engine.eval(new java.io.FileReader(new File("F:/test/test.js")));
        Invocable inv = (Invocable) engine;
        Object obj = engine.get("obj");
        inv.invokeMethod(obj, "name", "知道了");
    }


    /**
     * 腳本變量
     *
     * @throws Exception
     */
    @Test
    public void scriptVar() throws Exception {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("JavaScript");
        File file = new File("F:/test/test.txt");
        //將File對象f直接注入到js腳本中並可以作爲全局變量使用
        engine.put("files", file);
        engine.eval("print(files.getPath());print(files.getName());");
    }

    /**
     * 使用Script實現java接口
     *
     * @throws Exception
     */
    public void runnableImpl() throws Exception {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("JavaScript");

        // String裏定義一段JavaScript代碼腳本
        String script = "function run() { print('run called'); }";
        // 執行這個腳本
        engine.eval(script);

        // 從腳本引擎中獲取Runnable接口對象（實例）. 該接口方法由具有相匹配名稱的腳本函數實現。
        Invocable inv = (Invocable) engine;
        // 在上面的腳本中，我們已經實現了Runnable接口的run()方法
        Runnable runnable = inv.getInterface(Runnable.class);

        // 啓動一個線程運行上面的實現了runnable接口的script腳本
        Thread thread = new Thread(runnable);
        thread.start();
    }

    /**
     * 腳本引擎的多個scope
     *
     * @throws Exception
     */
    @Test
    public void multiScopes() throws Exception {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("nashorn");
        // 打印全局變量 "x"
        engine.put("x", "hello word!!");
        engine.eval("print(x);");
        // 上面的代碼會打印"hello word！！"

        // 現在，傳入另一個不同的script context
        ScriptContext context = new SimpleScriptContext();
        //新的Script context綁定ScriptContext的ENGINE_SCOPE
        Bindings bindings = context.getBindings(ScriptContext.ENGINE_SCOPE);

        // 增加一個新變臉到新的範圍 engineScope 中
        bindings.put("x", "word hello!!");
        // 執行同一個腳本 - 但這次傳入一個不同的script context
        engine.eval("print(x);", bindings);
        engine.eval("print(x);");
    }


    public static void main(String[] args) throws Exception {
        new JavaScriptFunction().runnableImpl();

        List list = new ArrayList();
        list.add("1");
        list.add("1");
        list.add("1");

        for (Object object : list) {
            System.out.println(object);
        }

    }

   

/**
 * @Author Evan
 * @Description //TODO 根據傳入代碼獲取結果
 * @Date 11:46 2019/10/14
 * @Param [paramJs] //TODO 一、單店要素 = IF ( M1<=Min,0,IF ( M1>=Mb,C,C- ( Mb - M1 ) / Fv * Fr ))
 * @return java.lang.String
 **/
public static BigDecimal getFunctionDecimal(String paramJs) throws ScriptException{
    ScriptEngineManager manager = new ScriptEngineManager();
    ScriptEngine engine = manager.getEngineByName("js");
    Object result = engine.eval(paramJs);
    if(EmptyUtil.isEmpty(result)){
        return new BigDecimal("0");
    }else{
        return new BigDecimal(result.toString()).setScale(2, BigDecimal.ROUND_HALF_UP);
    }
}

}

## 運用Java中的封裝技術將運行js腳本程序進行封裝

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import java.io.FileNotFoundException;
import java.io.FileReader;

/**
 * 運行腳本
 *
 * @author Ruby
 */
public class RunScript {

    private ScriptEngineManager manager = new ScriptEngineManager();
    private ScriptEngine engine;
    private String fileName;

    public RunScript(String fileName) {
        engine = manager.getEngineByName("JavaScript");
        this.fileName = fileName;
    }

    /**
     * 設置變量
     *
     * @param varName
     * @param obj
     */
    public void setVar(String varName, Object obj) {
        engine.put(varName, obj);
    }

    /**
     * 啓動腳本
     *
     * @throws FileNotFoundException
     * @throws ScriptException
     */
    public void start() throws FileNotFoundException, ScriptException {
        engine.eval(new FileReader(fileName));
    }
}

## 測試 將Logger對象注入到js對象中，那麼在js文件中就可以使用java中的Logger對象了

public static void main(String[]args)throws Exception{
        RunScript rs=new RunScript("D:\test.js");
        rs.setVar("Logger",Logger.getLogger(ConsoleListener.class));
        rs.start();
    }

    //在java中編譯js
    public static void main(String[]args)throws Exception
    {
        String expr="(1+2/5)*3";
        ScriptEngineManager manager=new ScriptEngineManager();
        ScriptEngine engine=manager.getEngineByName("js");
        Object result=engine.eval(expr);
        System.out.println(result);
    }