改善Java代码之慎用java动态编译

public class Client {

      public static void main(String[] args) throws Exception {

          //Java源代码

          String sourceStr = "public class Hello{    public String sayHello (String name) {return \"Hello,\" + name + \"!\";}}" ;

          //类名及文件名

          String clsName = "Hello" ;

          //方法名

          String methodName = "sayHello" ;

          //当前编译器

          JavaCompiler cmp = ToolProvider.getSystemJavaCompiler();

          //Java标准文件管理器

          StandardJavaFileManager fm = cmp.getStandardFileManager( null , null , null );

          //Java文件对象

          JavaFileObject jfo = new StringJavaObject(clsName,sourceStr);

          //编译参数，类似于javac <options>中的options

          List<String> optionsList = new ArrayList<String>();

          //编译文件的存放地方，注意：此处是为Eclipse工具特设的

          optionsList.addAll(Arrays.asList( "-d" , "./bin" ));

          //要编译的单元

          List<JavaFileObject> jfos = Arrays.asList(jfo);

          //设置编译环境

          JavaCompiler.CompilationTask task = cmp.getTask( null , fm, null , optionsList, null ,jfos);

          //编译成功

          if (task.call()){

              //生成对象

              Object obj = Class.forName(clsName).newInstance();

              Class<? extends Object> cls = obj.getClass();

              //调用sayHello方法

              Method m = cls.getMethod(methodName, String. class );

              String str = (String) m.invoke(obj, "Dynamic Compilation" );

              System.out.println(str);

         }

     }

}

//文本中的Java对象

class StringJavaObject extends SimpleJavaFileObject{

      //源代码

      private String content = "" ;

      //遵循Java规范的类名及文件

      public StringJavaObject(String _javaFileName,String _content){

            super (_createStringJavaObjectUri(_javaFileName),Kind.SOURCE);

            content = _content;

      }

      //产生一个URL资源路径

      private static URI _createStringJavaObjectUri(String name){

         //注意此处没有设置包名

         return URI.create( "String:///" + name + Kind.SOURCE.extension);

      }

      //文本文件代码

      @Override

      public CharSequence getCharContent( boolean ignoreEncodingErrors)

             throws IOException {

         return content;

     }

}