FastJson_python_内存溢出

哔哩哔哩学习：黑马FastJson教程https://www.bilibili.com/video/BV1Hy4y1x7ri?spm_id_from=333.1007.top_right_bar_window_history.content.click

Jackson学习https://blog.csdn.net/qq_40728285/article/details/124405831

一、FastJson介绍

FastJson是阿里巴巴的开源JSON解析库，它可以解析JSON格式字符串，支持将Java Bean 序列化为JSON字符串，也可以从JSON字符串反序列化到JavaBean

FastJson的优点

速度快
使用广泛
测试完备
使用简单
功能完善
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

二、FastJson序列化和反序列化

0、实体类

@Data
public class DgjTestEntity {
    private String name;
    private String sex;
    private int age;
    private String email;
    private String address;
    private Date birthday;
}

1、Java对象转Json字符串

public void objectToJson(){
    DgjTestEntity entity = new DgjTestEntity();
    entity.setName("DGS");
    entity.setAge(23);
    entity.setEmail("dgs@qq.com");
    // 对象 转换 Json字符串
    String jsonString = JSON.toJSONString(entity);
    System.out.println(jsonString);
    //{"age":23,"email":"dgs@qq.com","name":"DGS"}
}

2、List集合转Json字符串

public void listToJson(){
    List list = new ArrayList<>();
    DgjTestEntity entity1 = new DgjTestEntity();
    entity1.setName("DGS");
    entity1.setAge(23);
    entity1.setEmail("dgs@qq.com");

    DgjTestEntity entity2 = new DgjTestEntity();
    entity2 = new DgjTestEntity();
    entity2.setName("DGJ");
    entity2.setAge(23);
    entity2.setEmail("dgs@qq.com");

    list.add(entity1);
    list.add(entity2);
    // List集合 转换 Json字符串
    String jsonString = JSON.toJSONString(list);
    System.out.println(jsonString);
    //[{"age":23,"email":"dgs@qq.com","name":"DGS"},{"age":23,"email":"dgs@qq.com","name":"DGJ"}]
}

3、Map集合转Json字符串

public void mapToJson(){
    Map map = new HashMap<>();

    DgjTestEntity entity1 = new DgjTestEntity();
    entity1.setName("DGS");
    entity1.setAge(23);
    entity1.setEmail("dgs@qq.com");

    DgjTestEntity entity2 = new DgjTestEntity();
    entity2 = new DgjTestEntity();
    entity2.setName("DGJ");
    entity2.setAge(23);
    entity2.setEmail("dgs@qq.com");

    map.put("entity1",entity1);
    map.put("entity2",entity2);
    // List集合 转换 Json字符串
    String jsonString = JSON.toJSONString(map);
    System.out.println(jsonString);
    //{"entity1":{"age":23,"email":"dgs@qq.com","name":"DGS"},"entity2":{"age":23,"email":"dgs@qq.com","name":"DGJ"}}
}

4、Json格式字符串反序列化 Java对象

public void jsonToObject(){
    String jsonString = "{\"age\":23,\"email\":\"dgs@qq.com\",\"name\":\"DGS\"}";
    DgjTestEntity entity = JSON.parseObject(jsonString, DgjTestEntity.class);
    System.out.println(entity);
    //DgjTestEntity{name='DGS', sex='null', age=23, email='dgs@qq.com', address='null', birthday=null}
}

5、Json格式字符串反序列化 List集合

public void jsonToList(){
    String jsonString = "[{\"age\":23,\"email\":\"dgs@qq.com\",\"name\":\"DGS\"},{\"age\":23,\"email\":\"dgs@qq.com\",\"name\":\"DGJ\"}]";
    List list = JSON.parseArray(jsonString, DgjTestEntity.class);
    System.out.println(list);
    //[DgjTestEntity{name='DGS', sex='null', age=23, email='dgs@qq.com', address='null', birthday=null}, DgjTestEntity{name='DGJ', sex='null', age=23, email='dgs@qq.com', address='null', birthday=null}]
}

6、Json格式字符串反序列化 Map集合

public void jsonToMap(){
    String jsonString = "{\"entity1\":{\"age\":23,\"email\":\"dgs@qq.com\",\"name\":\"DGS\"},\"entity2\":{\"age\":23,\"email\":\"dgs@qq.com\",\"name\":\"DGJ\"}}";
    //JSON类的静态方法parseObject
    //直接进行反序列化，Map集合没有泛型的，泛型没有是不安全的集合
    //转后的集合必须要有泛型
    //调用parseObject，传递参数，TypeReference类型，在TypeReference类的泛型中，传递转正后的Map集合
    //没有parseMap 只有 调用parseObject 和 调用parseArray
    Map map = JSON.parseObject(jsonString, new TypeReference>() {});
    for (String key : map.keySet()){
        System.out.println(key+" "+ map.get(key));
    }
    //entity1 DgjTestEntity{name='DGS', sex='null', age=23, email='dgs@qq.com', address='null', birthday=null}
    //entity2 DgjTestEntity{name='DGJ', sex='null', age=23, email='dgs@qq.com', address='null', birthday=null}
}

三、SerializerFeature枚举

SerializerFeature 枚举：进行序列化时，可以自己定义特殊需求

作用于：JSON静态方法 toJSONString()

方法的参数：第一个是要序列化的对象

方法的参数：第二个参数是SerializerFeature枚举类型的可变参数

SerializerFeature枚举的常量，做序列化的个性需求

1、WriteMapNullValue 序列化Null的字段

public void objectToJson(){
    DgjTestEntity entity = new DgjTestEntity();
    entity.setName("DGS");
    entity.setAge(23);
    entity.setEmail("dgs@qq.com");
    String jsonString = JSON.toJSONString(entity, SerializerFeature.WriteMapNullValue);
    System.out.println(jsonString);
    //{"address":null,"age":23,"birthday":null,"email":"dgs@qq.com","name":"DGS","sex":null}
}

2、WriteNullStringAsEmpty 序列化字符串为Null的字段为空

    public void objectToJson(){
        DgjTestEntity entity = new DgjTestEntity();
        entity.setName("DGS");
        entity.setAge(23);
        entity.setEmail("dgs@qq.com");
        entity.setBirthday(new Date());
        String jsonString = JSON.toJSONString(entity,SerializerFeature.WriteMapNullValue,SerializerFeature.WriteNullStringAsEmpty,SerializerFeature.WriteDateUseDateFormat);
        System.out.println(jsonString);
        //{"address":"","age":23,"birthday":"2022-04-25 13:11:38","email":"dgs@qq.com","name":"DGS","sex":""}
    }

3、WriteNullNumberAsZero 序列化数值为Null的字段为0

public void objectToJson(){
    DgjTestEntity entity = new DgjTestEntity();
    entity.setName("DGS");
    entity.setEmail("dgs@qq.com");
    String jsonString = JSON.toJSONString(entity,SerializerFeature.WriteNullNumberAsZero);
    System.out.println(jsonString);
    //{"age":0,"email":"dgs@qq.com","name":"DGS"}
}

SerializerFeature.WriteNullBooleanAsFalse

布尔值为Null，序列化为false

SerializerFeature.WriteDateUseDateFormat

日期格式化："birthday":"2022-04-25 13:11:38"

SerializerFeature.PrettyFormat

JSON输出更加美观

{
   "age":0,
   "email":"dgs@qq.com",
   "name":"DGS"
}

四、@JSONField注解【作用于方法、字段和参数上面】

@JSONField(name = "userName") private String name; private int age; private Date birthday; private String email;	指定序列化后的名字：name ==> userName { "age":0, "birthday":1650865987972, "email":"dgs@qq.com", "userName":"DGS" }
@JSONField(name = "userName",ordinal = 0) private String name; @JSONField(ordinal = 1) private int age; private Date birthday; private String email;	指定序列化后字段顺序，属性值越小，顺序越靠前 { "birthday":1650866030820, "email":"dgs@qq.com", "userName":"DGS", "age":0 }
@JSONField(name = "userName",ordinal = 0) private String name; @JSONField(ordinal = 1) private int age; @JSONField(format = "yyyy-MM-dd") private Date birthday;	注解属性 format 指定序列化后的格式 { "birthday":"2022-04-25", "email":"dgs@qq.com", "userName":"DGS", "age":0 }
@JSONField(name = "userName",ordinal = 0) private String name; @JSONField(ordinal = 1) private int age; @JSONField(format = "yyyy-MM-dd") private Date birthday; @JSONField(serialize = false) private String email;	注解 serialize ，指定是否序列化该字段 { "birthday":"2022-04-25", "userName":"DGS", "age":0 }
	注解属性：deserialize，是否反序列化该字段
	注解属性：serialzeFeatures 徐丽华时的特性定义

五、@JSONType注解【作用于类上，定制序列和反序列化】

@Data
@JSONType
public class DgjTestEntity {
    private String name;
    private int age;
    private Date birthday;
    private String email;
    private String sex;
    private String address;
}

@JSONType(includes={"name","age","birthday"})
public class DgjTestEntity {
private String name;
private int age;
private Date birthday;
private String email;
private String sex;
private String address;
}

注解属性：includes 要被序列化的字段

{
   "age":0,
   "birthday":1650866941706,
   "name":"DGS"
}

@Data
@JSONType(includes = {"name","age","birthday"},
orders = {"name","age","birthday"})
public class DgjTestEntity {
private String name;
private int age;
private Date birthday;
private String email;
private String sex;
private String address;
}

注解属性：orders 序列化后的顺序

{
   "name":"DGS",
   "age":0,
   "birthday":1650867226406
}

注解属性：serialzeFeatures序列化时的特性定义

六、 FastJson 依赖


    com.alibaba
    fastjson
    1.2.62

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原文地址: http://outofmemory.cn/langs/743436.html

FastJson

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