一、 JSON解析器：

        * 常见的解析器：Jsonlib，Gson，fastjson，jackson

二、 JSON转为Java对象

  步骤：
        1. 导入jackson的相关jar包
        2. 创建Jackson核心对象 ObjectMapper
        3. 调用ObjectMapper的相关方法进行转换
		a. readValue(json字符串数据,Class)

三、 Java对象转换JSON

  1. 使用步骤：
		a. 导入jackson的相关jar包
		b. 创建Jackson核心对象 ObjectMapper
		c. 调用ObjectMapper的相关方法进行转换
			1. 转换方法：
				* writeValue(参数1，obj):
                       参数1：
                              File：将obj对象转换为JSON字符串，并保存到指定的文件中
                              Writer：将obj对象转换为JSON字符串，并将json数据填充到字符输出流中
                              OutputStream：将obj对象转换为JSON字符串，并将json数据填充到字节输出流中
                      * writeValueAsString(obj):将对象转为json字符串

四、例子

        public class JacksonTest {
             //Java对象转为JSON字符串
             @Test
             public void test1() throws Exception {
                //1.创建Person对象
                      Person p  = new Person();
                      p.setName("张三");
                      p.setAge(23);
                      p.setGender("男");

                //2.创建Jackson的核心对象  ObjectMapper
                ObjectMapper mapper = new ObjectMapper();
   
                //3.转换
                      /*

                          转换方法：
                                writeValue(参数1，obj):
                          参数1：
                                File：将obj对象转换为JSON字符串，并保存到指定的文件中
                                Writer：将obj对象转换为JSON字符串，并将json数据填充到字符输出流中
                                OutputStream：将obj对象转换为JSON字符串，并将json数据填充到字节输出流中
                            writeValueAsString(obj):将对象转为json字符串

                       */
                String json = mapper.writeValueAsString(p);

                //System.out.println(json);//{"name":"张三","age":23,"gender":"男"}



                //writeValue，将数据写到d://a.txt文件中
                //mapper.writeValue(new File("d://a.txt"),p);

                //writeValue.将数据关联到Writer中
                mapper.writeValue(new FileWriter("d://b.txt"),p);
      }


         @Test
         public void test2() throws Exception {
                //1.创建Person对象
                Person p = new Person();
                p.setName("张三");
                p.setAge(23);
                p.setGender("男");
                p.setBirthday(new Date());



               //2.转换
                ObjectMapper mapper = new ObjectMapper();
                String json = mapper.writeValueAsString(p);

                System.out.println(json);//{"name":"张三","age":23,"gender":"男","birthday":1530958029263}
                            //{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"}
         }



          @Test
          public void test3() throws Exception {
                //1.创建Person对象
                Person p = new Person();
                p.setName("张三");
                p.setAge(23);
                p.setGender("男");
                p.setBirthday(new Date());

                Person p1 = new Person();
                p1.setName("张三");
                p1.setAge(23);
                p1.setGender("男");
                p1.setBirthday(new Date());

                Person p2 = new Person();
                p2.setName("张三");
                p2.setAge(23);
                p2.setGender("男");
                p2.setBirthday(new Date());


                //创建List集合
                List<Person> ps = new ArrayList<Person>();
                ps.add(p);
                ps.add(p1);
                ps.add(p2);


                //2.转换
                ObjectMapper mapper = new ObjectMapper();
                String json = mapper.writeValueAsString(ps);
                // [{},{},{}]
                //[{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"},{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"},            {"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"}]
                System.out.println(json);
           }

         @Test
         public void test4() throws Exception {
                //1.创建map对象
                Map<String,Object> map = new HashMap<String,Object>();
                map.put("name","张三");
                map.put("age",23);
                map.put("gender","男");


                //2.转换
                ObjectMapper mapper = new ObjectMapper();
                String json = mapper.writeValueAsString(map);
                //{"name":"张三","age":23,"gender":"男"}
                System.out.println(json);//{"gender":"男","name":"张三","age":23}
         }

        
         //演示 JSON字符串转为Java对象
         @Test
         public void test5() throws Exception {
               //1.初始化JSON字符串
               String json = "{\"gender\":\"男\",\"name\":\"张三\",\"age\":23}";

               //2.创建ObjectMapper对象
               ObjectMapper mapper = new ObjectMapper();
               //3.转换为Java对象 Person对象
               Person person = mapper.readValue(json, Person.class);

              System.out.println(person);
        }

     }