需要包：
jackson-core-2.2.3.jar（核心jar包）
jackson-annotations-2.2.3.jar（该包提供Json注解支持）
jackson-databind-2.2.3.jar
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.9.1</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>2.9.1</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.1</version>
</dependency>
1、指定对象Class转成 json字符串
User user = new User();
user.setName("小民");
user.setEmail("xiaomin@sina.com");
user.setAge(20);
SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd");
user.setBirthday(dateformat.parse("1996-10-01"));
/**
- ObjectMapper是JSON操作的核心，Jackson的所有JSON操作都是在ObjectMapper中实现。
- ObjectMapper有多个JSON序列化的方法，可以把JSON字符串保存File、OutputStream等不同的介质中。
- writeValue(File arg0, Object arg1)把arg1转成json序列，并保存到arg0文件中。
- writeValue(OutputStream arg0, Object arg1)把arg1转成json序列，并保存到arg0输出流中。
- writeValueAsBytes(Object arg0)把arg0转成json序列，并把结果输出成字节数组。
- writeValueAsString(Object arg0)把arg0转成json序列，并把结果输出成字符串。
*/
ObjectMapper mapper = new ObjectMapper();
//User类转JSON
{"name":"小民","age":20,"birthday":844099200000,"email":"xiaomin@sina.com"}
String json = mapper.writeValueAsString(user);
System.out.println(json);
输出：
{"name":"小民","age":20,"birthday":844099200000,"email":"xiaomin@sina.com"}
2、List集合转化成json字符串
List<User> users = new ArrayList<User>();
users.add(user);
String jsonlist = mapper.writeValueAsString(users);
System.out.println(jsonlist);
输出：
[{"name":"小民","age":20,"birthday":844099200000,"email":"xiaomin@sina.com"}]
3、Json字符串转化成指定Class类
String json = "{\"name\":\"小民\",\"age\":20,\"birthday\":844099200000,\"email\":\"xiaomin@sina.com\"}";
/**
* ObjectMapper支持从byte[]、File、InputStream、字符串等数据的JSON反序列化。
*/
ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(json, User.class);
System.out.println(user);
输出：
User{name='小民aa', age=25, birthday=Tue Oct 01 00:00:00 CST 1996, email='xiaomin@sina.com'}
4、Json字符串转化成集合List
方法一：
String jsonString="[{'id':'1'},{'id':'2'}]";
ObjectMapper mapper = new ObjectMapper();
JavaType javaType = mapper.getTypeFactory().constructParametricType(List.class, Bean.class);
//如果是Map类型 mapper.getTypeFactory().constructParametricType(HashMap.class,String.class, Bean.class);
List<Bean> lst = (List<Bean>)mapper.readValue(jsonString, javaType);
输出：
Student{name='s1', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s2', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s3', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s4', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s5', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s6', age=12, date=Thu Jun 09 20:38:37 CST 2016}
方法二：
String jsonString="[{'id':'1'},{'id':'2'}]";
ObjectMapper mapper = new ObjectMapper();
List<Bean> beanList = mapper.readValue(jsonString, new TypeReference<List<Bean>>() {});
输出：
Student{name='s1', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s2', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s3', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s4', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s5', age=12, date=Thu Jun 09 20:38:37 CST 2016}
Student{name='s6', age=12, date=Thu Jun 09 20:38:37 CST 2016}
