Java 如何实现动态脚本？

eval('console.log(2+3)')

--dynamic-script 
 ------advance-discuss //深度讨论脚本动态化技术中的一些细节 
 ------code-javac //使用代码执行编译加载运行任务 
 ------command-javac //演示用命令行的方式动态编译和加载java类 
 ------facade  //提供单独的接口包，方便整个演示过程流畅进行

cd 项目根目录 
 mvn install

# 进入到Cat.java所在的目录 
 cd /Users/fusu/d/group/fusu-share/dynamic-script/command-javac/src/main/resources 
 # 使用命令行工具javac编译，linux/mac 上cp分隔符使用 :  windown使用 ; 
 javac -cp .:/Users/fusu/d/group/fusu-share/dynamic-script/facade/target/facade-1.0.jar Cat.java 
 # 运行 
 java -cp .:/Users/fusu/d/group/fusu-share/dynamic-script/facade/target/facade-1.0.jar Cat 
 # 得到结果 
 # > I'm Cat Main

//项目所在路径 
 String projectPath = PathUtil.getAppHomePath(); 
  
 Process process = null; 
  
 String cmd = String.format("javac -cp .:%s/facade/target/facade-1.0.jar -d %s/command-javac/src/main/resources %s/command-javac/src/main/resources/Cat.java", projectPath, projectPath, projectPath); 
  
 System.out.println(cmd); 
  
 process = Runtime.getRuntime().exec(cmd); 
  
 // 打印程序输出 
 readProcessOutput(process); 
  
 int exitVal = process.waitFor(); 
 if (exitVal == 0) { 
   System.out.println("javac执行成功！" + exitVal); 
 } else { 
   System.out.println("javac执行失败" + exitVal); 
   return; 
 } 
  
 String classFilePath = String.format("%s/command-javac/src/main/resources/Cat.class", projectPath); 
 String urlFilePath = String.format("file:%s", classFilePath); 
 URL url = new URL(urlFilePath); 
 URLClassLoader classLoader = new URLClassLoader(new URL[]{url}); 
  
 Class<?> catClass = classLoader.loadClass("Cat"); 
 Object obj = catClass.newInstance(); 
 if (obj instanceof Animal) { 
   Animal animal = (Animal) obj; 
   animal.hello("Kitty"); 
 } 
 //会得到结果:  Hello,Kitty! 我是Cat。

//类名 
 String className = "Cat"; 
 //项目所在路径 
 String projectPath = PathUtil.getAppHomePath(); 
 String facadeJarPath = String.format(".:%s/facade/target/facade-1.0.jar", projectPath); 
  
 //需要进行编译的代码 
 Iterable<? extends JavaFileObject> compilationUnits = new ArrayList<JavaFileObject>() {{ 
   add(new JavaSourceFromString(className, getJavaCode())); 
 }}; 
  
 //编译的选项，对应于命令行参数 
 List<String> options = new ArrayList<>(); 
 options.add("-classpath"); 
 options.add(facadeJarPath); 
  
 //使用系统的编译器 
 JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler(); 
  
 StandardJavaFileManager standardJavaFileManager = javaCompiler.getStandardFileManager(null, null, null); 
 ScriptFileManager scriptFileManager = new ScriptFileManager(standardJavaFileManager); 
  
 //使用stringWriter来收集错误。 
 StringWriter errorStringWriter = new StringWriter(); 
  
 //开始进行编译 
 boolean ok = javaCompiler.getTask(errorStringWriter, scriptFileManager, diagnostic -> { 
   if (diagnostic.getKind() == Diagnostic.Kind.ERROR) { 
  
     errorStringWriter.append(diagnostic.toString()); 
   } 
 }, options, null, compilationUnits).call(); 
  
 if (!ok) { 
   String errorMessage = errorStringWriter.toString(); 
   //编译出错，直接抛错。 
   throw new RuntimeException("Compile Error:{}" + errorMessage); 
 } 
  
 //获取到编译后的二进制数据。 
 final Map<String, byte[]> allBuffers = scriptFileManager.getAllBuffers(); 
 final byte[] catBytes = allBuffers.get(className); 
  
 //使用自定义的ClassLoader加载类 
 FsClassLoader fsClassLoader = new FsClassLoader(className, catBytes); 
 Class<?> catClass = fsClassLoader.findClass(className); 
 Object obj = catClass.newInstance(); 
 if (obj instanceof Animal) { 
   Animal animal = (Animal) obj; 
   animal.hello("Moss"); 
 } 
  
 //会得到结果:  Hello,Moss! 我是Cat。

/*FsClassLoader.java*/ 
 public FsClassLoader(ClassLoader parentClassLoader, String name, byte[] data) { 
   super(parentClassLoader); 
   this.fullyName = name; 
   this.data = data; 
 } 
  
  
 /*AdvanceDiscuss.java*/ 
  
 //接口的类加载器 
 ClassLoader animalClassLoader = Animal.class.getClassLoader(); 
 //设置当前的线程类加载器 
 Thread.currentThread().setContextClassLoader(animalClassLoader); 
 //... 
 //使用自定义的ClassLoader加载类 
 FsClassLoader fsClassLoader = new FsClassLoader(animalClassLoader, className, cat

for (int i = 0; i < 1000000; i++) { 
   //编译加载并且执行 
   compileAndRun(i); 
  
   //10000个回收一下 
   if (i % 10000 == 0) { 
     System.gc(); 
   } 
 } 
  
 //强制进行回收 
 System.gc(); 
 System.out.println("休息10s"); 
 Thread.currentThread().sleep(10 * 1000);

public static Set<String> getDependencies(InputStream is) throws Exception { 
  
   ClassFile cf = new ClassFile(new DataInputStream(is)); 
   ConstPool constPool = cf.getConstPool(); 
   HashSet<String> set = new HashSet<>(); 
   for (int ix = 1, size = constPool.getSize(); ix < size; ix++) { 
     int descriptorIndex; 
     if (constPool.getTag(ix) == ConstPool.CONST_Class) { 
       set.add(constPool.getClassInfo(ix)); 
     } else if (constPool.getTag(ix) == ConstPool.CONST_NameAndType) { 
       descriptorIndex = constPool.getNameAndTypeDescriptor(ix); 
       String desc = constPool.getUtf8Info(descriptorIndex); 
       for (int p = 0; p < desc.length(); p++) { 
         if (desc.charAt(p) == 'L') { 
           set.add(desc.substring(++p, p = desc.indexOf(';', p)).replace('/', '.')); 
         } 
       } 
     } 
   } 
   return set; 
 }

java.lang, 
 java.util, 
 com.alibaba.fastjson, 
 java.text, 
 [Ljava.lang (java.lang下的数组，例如 `String[]`) 
 [D (double[]) 
 [F (float[]) 
 [I (int[]) 
 [J (long[]) 
 [C (char[]) 
 [B (byte[]) 
 [Z (boolean[])

java.lang.Thread 
 java.lang.reflect