什么是腳本引擎，腳本引擎是指在程序運(yùn)行期間嵌入另一種腳本語言，并與其交互，產(chǎn)生最終運(yùn)行結(jié)果

腳本引擎存在的意義是什么？腳本引擎可以改變編譯語言的內(nèi)部運(yùn)行邏輯，彌補(bǔ)編譯語言的不足，使編譯語言具備動(dòng)態(tài)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(fā)的端游（網(wǎng)游一種，需要按照客戶端），編譯語言最大的缺點(diǎn)就是客戶端升級(jí)需要重新安裝并且安裝之后重啟應(yīng)用程序才能生效。腳本引擎彌補(bǔ)了這項(xiàng)致命的缺點(diǎn)，用戶只需升級(jí)劇情腳本，而不需要退出整個(gè)游戲然后重新進(jìn)入。

1.11.1.?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>

1.11.2.?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);}} }

1.11.3.?運(yùn)行腳本文件

將腳本放入外部文件

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 stubScriptEngineManager 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 blocke.printStackTrace();} catch (ScriptException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

test.js

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

1.11.4.?變量傳遞

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 scriptengine.put("file", f);// evaluate a script string. The script accesses "file"// variable and calls method on itengine.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 stubtry {ScriptVars sv = new ScriptVars();sv.variable();sv.simpleBindings();sv.outputToFile();sv.function();sv.object();sv.outputToFile();} catch (ScriptException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

1.11.5.?全局變量與局部變量定義

ScriptContext.GLOBAL_SCOPE 作用于 ScriptEngineManager， ScriptContext.ENGINE_SCOPE 作用于 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 stubScriptEngineManager 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 并沒有定義 name 但輸出結(jié)果卻顯示 Netkiller，所以ScriptContext.GLOBAL_SCOPE定義的變量是全局的。 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 contextScriptContext newContext = new SimpleScriptContext();Bindings engineScope = newContext.getBindings(ScriptContext.ENGINE_SCOPE);// add new variable "x" to the new engineScopeengineScope.put("x", "world");// execute the same script - but this time pass a different script contextengine.eval("print(x);", newContext);// the above line prints "world"} }

1.11.6.?調(diào)用腳本中的函數(shù)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 stubScriptEngineManager manager = new ScriptEngineManager();ScriptEngine engine = manager.getEngineByName("JavaScript");// JavaScript code in a StringString script = "function hello(name) { print('Hello, ' + name); }";// evaluate scriptengine.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 scriptengine.eval(script);// get script object on which we want to call the methodObject obj = engine.get("obj");// invoke the method named "hello" on the script object "obj"inv.invokeMethod(obj, "hello", "Script Method !!");} }

1.11.7.?腳本編譯

只有重復(fù)執(zhí)行腳本時(shí)才需要編譯。只運(yùn)行一次不建議編譯運(yùn)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 stubScriptCompile sc = new ScriptCompile();try {CompiledScript script = sc.compile("print('Helloworld!!!');");for (int i = 0; i < 100; i++) {script.eval();}} catch (ScriptException ex) {ex.printStackTrace();}}}

1.11.8.?jjs - Invokes the Nashorn engine.

jjs 是一個(gè)在命令行運(yùn)行腳本的命令

創(chuàng)建腳本文件

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

運(yùn)行結(jié)果

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

原文出處：Netkiller 系列 手札
本文作者：陳景峯
轉(zhuǎn)載請(qǐng)與作者聯(lián)系，同時(shí)請(qǐng)務(wù)必標(biāo)明文章原始出處和作者信息及本聲明。

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