fastjson

java bean序列化为json字符串，json字符串反序列化为java bean

优点：

速度快
使用简单
功能完备
支持泛型，支持流处理超大文本，支持枚举，支持序列化和反序列化扩展

导包

<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.75</version>
</dependency>

springboot中的配置

MyWebMvcConfig

@Bean
public HttpMessageConverter configureMessageConverters() {
FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
FastJsonConfig config = new FastJsonConfig();
config.setSerializerFeatures(
// 保留map空的字段
SerializerFeature.WriteMapNullValue,
// 将String类型的null转成""
SerializerFeature.WriteNullStringAsEmpty,
// 将Number类型的null转成0
SerializerFeature.WriteNullNumberAsZero,
// 将List类型的null转成[]
SerializerFeature.WriteNullListAsEmpty,
// 将Boolean类型的null转成false
SerializerFeature.WriteNullBooleanAsFalse,
// 避免循环引用
SerializerFeature.DisableCircularReferenceDetect);

converter.setFastJsonConfig(config);
converter.setDefaultCharset(Charset.forName("UTF-8"));
List<MediaType> mediaTypeList = new ArrayList<>();
// 解决中文乱码问题，相当于在Controller上的@RequestMapping中加了个属性produces = "application/json"
mediaTypeList.add(MediaType.APPLICATION_JSON);
converter.setSupportedMediaTypes(mediaTypeList);
return converter;
}

对象和json的转换

// 对象
User user1 = new User(11, "lisi");
User user2 = new User(12, "zhangsan");
String s = JSON.toJSONString(user1);
System.out.println("对象变为json字符串" + s);
User user = JSON.parseObject(s, User.class);
System.out.println("json字符串变为对象" + user);

JSONObject jsonObject = (JSONObject)JSON.toJSON(user1);
System.out.println("java对象变为json对象" + jsonObject);
User user3 = JSON.toJavaObject(jsonObject, User.class);
System.out.println("json对象变为java对象" + user3);

// list
List list = new ArrayList();
list.add(user1);
list.add(user2);
String s1 = JSON.toJSONString(list);
System.out.println("list变为json字符串" + s1);// []是个数组
List<User> users = JSON.parseArray(s1, User.class);
System.out.println("json字符串变为list" + users);

// map
Map map = new HashMap();
map.put("user1", user1);
map.put("user2", user2);
String smap = JSON.toJSONString(map);
System.out.println("map变为json字符串" + smap);
Map<String, Student> map = JSON.parseObject(smp, new TypeReference<Map<String, User>>());
System.out.println("json字符串变为map" + users);

JSONObject

JSONObject jsonObject = new JSONObject();
jsonObject.put("userName", "中文");
jsonObject.put("password", "1 + 1");
// JSONObject 转为json字符串
jsonObject.toJSONString();

// JSONObject转为map
Map<String,String> = jsonObject.parseObject(jsonObject.toJSONString(), new TypeReference<Map<String,String>>);

SerializerFeature

枚举常量个性化定制

空双引号

将空integer赋值为0

日期格式化

一对对的pretty格式

public class FastjsonTest {
public static void main(String[] args) {
UserRequest u1 = new UserRequest();
u1.setId(1L);
u1.setPassword("u1");
String s = JSON.toJSONString(u1);
System.out.println(s);
}
}
// {"id":1,"password":"u1"} 为null的不会被序列化为json字符串

// 序列化null
// {"id":1,"password":"u1","userName":null}
String s = JSON.toJSONString(u1, SerializerFeature.WriteMapNullValue);

// 序列化为""
// {"id":1,"password":"u1","userName":""}
String s = JSON.toJSONString(u1, SerializerFeature.WriteNullStringAsEmpty);

// 序列化 number 为0
public static void main(String[] args) {
UserRequest u1 = new UserRequest();
u1.setPassword("u1");
String s = JSON.toJSONString(u1, SerializerFeature.WriteNullNumberAsZero);
System.out.println(s);
}
// {"id":0,"password":"u1"}

WriteNullBooleanAsFalse // 属性为Boolean的没有值则被序列化为false
WriteDateUseDateFormat // 将原来的日期序列化为年月日时分秒

// 显示Pretty格式化
public static void main(String[] args) {
UserRequest u1 = new UserRequest();
u1.setPassword("u1");
String s = JSON.toJSONString(u1, SerializerFeature.WriteNullNumberAsZero, SerializerFeature.PrettyFormat);
System.out.println(s);
}
/*
{
"id":0,
"password":"u1"
}
*/

------------------------------- ------------------------------- ------------------------------- -------------------------------

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private String email;
    private Date birthday;

}


public class fastJson {

    public Date getDate() {
        Date date = new Date();
        return date;
    }

    @Test
    public void testObjtoJson() {
        Student student = new Student();
        student.setAge(19);
        student.setName("zzz");
        student.setId(1);
        student.setEmail("88.com");
        student.setBirthday(getDate());
        String s = JSON.toJSONString(student);
        System.out.println(s);
    }

    @Test
    public void testListToJson() {
        Student student1 = new Student();
        student1.setAge(19);
        student1.setName("zzz");
        student1.setId(1);
        student1.setEmail("88.com");
        student1.setBirthday(getDate());

        Student student2 = new Student();
        student2.setAge(20);
        student2.setName("zzz2");
        student2.setId(2);
        student2.setEmail("99.com");
        student2.setBirthday(getDate());
        List<Student> list = new ArrayList<Student>();
        list.add(student1);
        list.add(student2);
        String s = JSON.toJSONString(list);
        System.out.println(s);
    }
    @Test
    public void testMapToJson(){
        Student student1 = new Student();
        student1.setAge(19);
        student1.setName("zzz");
        student1.setId(1);
        student1.setEmail("88.com");
        student1.setBirthday(getDate());

        Student student2 = new Student();
        student2.setAge(20);
        student2.setName("zzz2");
        student2.setId(2);
        student2.setEmail("99.com");
        student2.setBirthday(getDate());
        HashMap<String, Student> map = new HashMap<>();
        map.put("s1",student1);
        map.put("s2",student2);
        String s = JSON.toJSONString(map);
        System.out.println(s);

    }
    @Test
    public void testJsonToObj() {
   String obj = "{\"age\":19,\"birthday\":1652368762320,\"email\":\"88.com\",\"id\":1,\"name\":\"zzz\"}\n";
        Student student = JSON.parseObject(obj, Student.class);
        Student student1 = JSONObject.parseObject(obj, Student.class);
        System.out.println(student);
        System.out.println(student1);
    }

    @Test
    public void testListToObj() {
   String obj = "[{\"age\":19,\"birthday\":1652369165457,\"email\":\"88.com\",\"id\":1,\"name\":\"zzz\"},{\"age\":20,\"birthday\":1652369165457,\"email\":\"99.com\",\"id\":2,\"name\":\"zzz2\"}]\n";
//        Student student = JSON.parseObject(obj, Student.class);
//        Student student1 = JSONObject.parseObject(obj, Student.class);
//        System.out.println(student);
//        System.out.println(student1);
        List<Student> students = JSON.parseArray(obj, Student.class);
        List<Student> students2 = JSONObject.parseArray(obj, Student.class);
        System.out.println(students);
        System.out.println(students2);
    }

    @Test
    public void testMapToObj() {
   String obj = "{\"s1\":{\"age\":19,\"birthday\":1652369958048,\"email\":\"88.com\",\"id\":1,\"name\":\"zzz\"},\"s2\":{\"age\":20,\"birthday\":1652369958048,\"email\":\"99.com\",\"id\":2,\"name\":\"zzz2\"}}\n";
        Map map =  JSON.parseObject(obj);
        Map map2 =  JSONObject.parseObject(obj);
        Map<String, Student> stringStudentMap = JSON.parseObject(obj, new TypeReference<Map<String, Student>>(){});
        Map<String, Student> stringStudentMap5 = JSON.parseObject(obj, new TypeReference<Map<String, Student>>(){});
        Map<String, Student> contentMap = new HashMap<>();
        Map<String, Student> stringStudentMap2 = (Map<String, Student>) JSONObject.parseObject(obj, contentMap.getClass());
        for(String key: stringStudentMap.keySet()){
            System.out.println(key+"::"+stringStudentMap.get(key));
        }
        for(String key2: stringStudentMap5.keySet()){
            System.out.println(key2+"::"+stringStudentMap5.get(key2));
        }
    }
}