package com.java.test.dynamicpojo;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.OutputStream;

import java.lang.reflect.Method;

import java.net.URI;

import java.util.Arrays;

import javax.tools.FileObject;

import javax.tools.ForwardingJavaFileManager;

import javax.tools.JavaCompiler;

import javax.tools.JavaFileManager;

import javax.tools.JavaFileObject;

import javax.tools.SimpleJavaFileObject;

import javax.tools.StandardJavaFileManager;

import javax.tools.ToolProvider;

public class DynamicPOJO {

        private static String classString = "/* hehha */" + "public class Student{                                  "

                + "       private String  studentId;                      "

                + "       public String getStudentId(){                   "

                + "           return \"小明\";                      "

                + "       }                                               "

                + "}                                                    ";

        private static void createStudent() throws Exception {

            JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

            StandardJavaFileManager standardFileManager = compiler.getStandardFileManager(null, null, null);

            ClassJavaFileManager classJavaFileManager = new ClassJavaFileManager(standardFileManager);

            StringObject stringObject = new StringObject(new URI("Student.java"), JavaFileObject.Kind.SOURCE, classString);

            JavaCompiler.CompilationTask task = compiler.getTask(null, classJavaFileManager, null, null, null,

                    Arrays.asList(stringObject));

            if (task.call()) {

                ClassJavaFileObject javaFileObject = classJavaFileManager.getClassJavaFileObject();

                ClassLoader classLoader = new MyClassLoader(javaFileObject);

                Object student = classLoader.loadClass("Student").newInstance();

                System.out.println("student-->"+student);//student对象

                Method getStudetnId = student.getClass().getMethod("getStudentId");

                Object invoke = getStudetnId.invoke(student);

                System.out.println("getStudentId-->"+invoke);

            }

        }

        /**    *自定义fileManager    */

        static class ClassJavaFileManager extends ForwardingJavaFileManager{

            private ClassJavaFileObject classJavaFileObject;

            public ClassJavaFileManager(JavaFileManager fileManager) {

                super(fileManager);

            }

            public ClassJavaFileObject getClassJavaFileObject() {

                return classJavaFileObject;

            }

            /**这个方法一定要自定义 */

            @Override

            public JavaFileObject getJavaFileForOutput(Location location, String className,

                    JavaFileObject.Kind kind, FileObject sibling) throws IOException {

                return (classJavaFileObject = new ClassJavaFileObject(className,kind));

            }

        }  

        /**     * 存储源文件     */

        static class StringObject extends SimpleJavaFileObject{

            private String content;

            public StringObject(URI uri, Kind kind, String content) {

                super(uri, kind);

                this.content = content;

            }

            @Override

            public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {

                return this.content;

            }

        }   

        /**     * class文件（不需要存到文件中）     */

        static class ClassJavaFileObject extends SimpleJavaFileObject{

            ByteArrayOutputStream outputStream;

            public ClassJavaFileObject(String className, Kind kind) {

                super(URI.create(className + kind.extension), kind);

                this.outputStream = new ByteArrayOutputStream();

            }        //这个也要实现

            @Override

            public OutputStream openOutputStream() throws IOException {

                return this.outputStream;

            }

            public byte[] getBytes(){

                return this.outputStream.toByteArray();

                }

        }   

        /**自定义classloader*/

        static class MyClassLoader extends ClassLoader{

            private ClassJavaFileObject stringObject;

            public MyClassLoader(ClassJavaFileObject stringObject){

                this.stringObject = stringObject;

            }

            @Override

            protected Class<?> findClass(String name) throws ClassNotFoundException {

                byte[] bytes = this.stringObject.getBytes();

                return defineClass(name,bytes,0,bytes.length);

            }

        }

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

            createStudent();

        }

}