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1.16. java 腳本引擎
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1.16. java 腳本引擎

什麼是腳本引擎，腳本引擎是指在程序運行期間嵌入另一種腳本語言，並與其交互，產生最終運行結果

腳本引擎存在的意義是什麼？腳本引擎可以改變編譯語言的內部運行邏輯，彌補編譯語言的不足，使編譯語言具備動態語言的一部分特性。

是否有成功案例？最成功的案例就是基于C++和Lua語言開發的端游（網遊一種，需要按照客戶端），編譯語言最大的缺點就是客戶端升級需要重新安裝並且安裝之後重啟應用程序才能生效。腳本引擎彌補了這項致命的缺點，用戶只需升級劇情腳本，而不需要退出整個遊戲然後重新進入。

1.16.1. Maven

		
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>cn.netkiller</groupId>
	<artifactId>script</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>Java Script</name>
	<description>Java Script Engine</description>
	<dependencies>
		<!-- https://mvnrepository.com/artifact/org.mockito/mockito-all -->
		<dependency>
			<groupId>org.mockito</groupId>
			<artifactId>mockito-all</artifactId>
			<version>1.10.19</version>
		</dependency>
	</dependencies>
	<build>
		<sourceDirectory>src</sourceDirectory>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.5.1</version>
				<configuration>
					<source>1.8</source>
					<target>1.8</target>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

1.16.2. Helloworld

		
package cn.netkiller.javascript;

import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class Helloworld {

	public Helloworld() {
		ScriptEngineManager manager = new ScriptEngineManager();
		List<ScriptEngineFactory> factories = manager.getEngineFactories();
		for (ScriptEngineFactory f : factories) {
			System.out.println("egine name:" + f.getEngineName());
			System.out.println("engine version:" + f.getEngineVersion());
			System.out.println("language name:" + f.getLanguageName());
			System.out.println("language version:" + f.getLanguageVersion());
			System.out.println("names:" + f.getNames());
			System.out.println("mime:" + f.getMimeTypes());
			System.out.println("extension:" + f.getExtensions());
			System.out.println("-----------------------------------------------");
		}
	}

	public void hello() throws ScriptException {
		ScriptEngineManager manager = new ScriptEngineManager();
		ScriptEngine engine = manager.getEngineByName("JavaScript");
		// ScriptEngine engine = manager.getEngineByExtension("js");
		// ScriptEngine engine = manager.getEngineByMimeType("text/javascript");
		engine.eval("print('Hello, World')");
	}

	public static void main(String[] args) {
		try {
			new Helloworld().hello();
		} catch (ScriptException ex) {
			Logger.getLogger(Helloworld.class.getName()).log(Level.SEVERE, null, ex);
		}
	}
}

1.16.3. 運行腳本檔案

將腳本放入外部檔案

		
package javascript;

import java.io.FileNotFoundException;
import java.net.URL;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class EvalFile {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ScriptEngineManager manager = new ScriptEngineManager();
		ScriptEngine engine = manager.getEngineByExtension("js");
		// ScriptEngine engine = manager.getEngineByMimeType("text/javascript");

		try {

			URL location = EvalFile.class.getProtectionDomain().getCodeSource().getLocation();
			String file = location.getFile() + "test.js";
			System.out.println(file);

			engine.eval(new java.io.FileReader(file));

		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ScriptException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

test.js

print("This is hello from test.js");

1.16.4. 變數傳遞

		
package javascript;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.script.Bindings;
import javax.script.ScriptContext;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import javax.script.SimpleBindings;

public class ScriptVars {

	ScriptEngine engine = null;

	public ScriptVars() {
		ScriptEngineManager manager = new ScriptEngineManager();
		engine = manager.getEngineByMimeType("text/javascript");
	}

	public void variable() throws ScriptException {
		engine.put("name", "Neo");
		engine.eval("var message = 'Hello, ' + name;");
		engine.eval("print(message);");
		Object obj = engine.get("message");
		System.out.println(obj);
	}

	public void simpleBindings() throws ScriptException {
		Bindings bindings = new SimpleBindings();
		bindings.put("name", "Neo");
		engine.eval("print('I am ' + name);", bindings);
	}

	public void function() throws ScriptException {
		engine.put("a", 4);
		engine.put("b", 6);
		Object maxNum = engine.eval("function max_num(a,b){return (a>b)?a:b;}max_num(a,b);");
		System.out.println("max_num:" + maxNum + ", (class = " + maxNum.getClass() + ")");

		Map<String, Integer> m = new HashMap<String, Integer>();
		m.put("c", 10);
		engine.put("m", m);
		engine.eval("var x= max_num(a,m.get('c'));");
		System.out.println("max_num:" + engine.get("x"));
	}

	public void object() throws ScriptException {
		File f = new File("test.txt");
		// expose File object as variable to script
		engine.put("file", f);

		// evaluate a script string. The script accesses "file"
		// variable and calls method on it
		engine.eval("print(file.getAbsolutePath())");
	}

	public void outputToFile() throws IOException, ScriptException {
		ScriptContext context = engine.getContext();
		context.setWriter(new FileWriter("script.log"));
		engine.eval("print('Hello World!');");
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		try {
			ScriptVars sv = new ScriptVars();
			sv.variable();
			sv.simpleBindings();
			sv.outputToFile();
			sv.function();
			sv.object();
			sv.outputToFile();

		} catch (ScriptException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

1.16.5. 全局變數與局部變數定義

ScriptContext.GLOBAL_SCOPE 作用於 ScriptEngineManager， ScriptContext.ENGINE_SCOPE 作用於 ScriptEngine

		
package javascript;

import javax.script.ScriptContext;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class ContextVariable {

	public static void main(String[] args) throws ScriptException {
		// TODO Auto-generated method stub
		ScriptEngineManager manager = new ScriptEngineManager();
		ScriptEngine engine = manager.getEngineByName("JavaScript");
		ScriptContext context = engine.getContext();  
	    context.setAttribute("name", "Netkiller", ScriptContext.GLOBAL_SCOPE);  
	    context.setAttribute("name", "Neo", ScriptContext.ENGINE_SCOPE);  
	    //context.getAttribute("name"); 
	    engine.eval("print('I am ' + name);", context);
	    
	    // engine1,context1 並沒有定義 name 但輸出結果卻顯示 Netkiller，所以ScriptContext.GLOBAL_SCOPE定義的變數是全局的。 
	    ScriptEngine engine1 = manager.getEngineByName("JavaScript");
	    ScriptContext context1 = engine1.getContext();  
	    engine.eval("print('I am ' + name);", context1);
	    
	}

}		
		
		
		
import javax.script.*;

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

        engine.put("x", "hello");
        // print global variable "x"
        engine.eval("print(x);");
        // the above line prints "hello"

        // Now, pass a different script context
        ScriptContext newContext = new SimpleScriptContext();
        Bindings engineScope = newContext.getBindings(ScriptContext.ENGINE_SCOPE);

        // add new variable "x" to the new engineScope
        engineScope.put("x", "world");

        // execute the same script - but this time pass a different script context
        engine.eval("print(x);", newContext);
        // the above line prints "world"
    }
}

1.16.6. 調用腳本中的函數或方法

		
package javascript;

import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class InvokeScriptFunction {

	public static void main(String[] args) throws ScriptException, NoSuchMethodException {
		// TODO Auto-generated method stub
		ScriptEngineManager manager = new ScriptEngineManager();
		ScriptEngine engine = manager.getEngineByName("JavaScript");

		// JavaScript code in a String
		String script = "function hello(name) { print('Hello, ' + name); }";
		// evaluate script
		engine.eval(script);

		// javax.script.Invocable is an optional interface.
		// Check whether your script engine implements or not!
		// Note that the JavaScript engine implements Invocable interface.
		Invocable inv = (Invocable) engine;

		// invoke the global function named "hello"
		inv.invokeFunction("hello", "Scripting!!");

		// JavaScript code in a String. This code defines a script object 'obj'
		// with one method called 'hello'.
		script = "var obj = new Object(); obj.hello = function(name) { print('Hello, ' + name); }";
		// evaluate script
		engine.eval(script);
		// get script object on which we want to call the method
		Object obj = engine.get("obj");

		// invoke the method named "hello" on the script object "obj"
		inv.invokeMethod(obj, "hello", "Script Method !!");
	}
}

1.16.7. 腳本編譯

只有重複執行腳本時才需要編譯。只運行一次不建議編譯運行。

		
package javascript;

import javax.script.*;

public class ScriptCompile {
	public CompiledScript compile(String script) throws ScriptException {

		ScriptEngineManager manager = new ScriptEngineManager();
		ScriptEngine engine = manager.getEngineByName("JavaScript");

		return ((Compilable) engine).compile(script);

	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ScriptCompile sc = new ScriptCompile();
		try {

			CompiledScript script = sc.compile("print('Helloworld!!!');");

			for (int i = 0; i < 100; i++) {
				script.eval();
			}

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

}

1.16.8. jjs - Invokes the Nashorn engine.

jjs 是一個在命令行運行腳本的命令

創建腳本檔案

		
[neo@netkiller tmp]$ cat test.js 
function f() { 
     return 1; 
}; 

print( f() + 1 );

運行結果

		
[neo@netkiller tmp]$ jjs test.js 
2

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