Java中Jackson的序列化与反序列化详解

private static final ObjectMapper mapper;
public static ObjectMapper getObjectMapper(){
    return this.mapper;
}
static{
    //创建ObjectMapper对象
    mapper = new ObjectMapper()
    //configure方法 配置一些需要的参数
    // 转换为格式化的json 显示出来的格式美化
    mapper.enable(SerializationFeature.INDENT_OUTPUT);
    //序列化的时候序列对象的那些属性  
    //JsonInclude.Include.NON_DEFAULT 属性为默认值不序列化 
    //JsonInclude.Include.ALWAYS      所有属性
    //JsonInclude.Include.NON_EMPTY   属性为 空（“”） 或者为 NULL 都不序列化 
    //JsonInclude.Include.NON_NULL    属性为NULL 不序列化
    mapper.setSerializationInclusion(JsonInclude.Include.ALWAYS);  
    //反序列化时,遇到未知属性会不会报错 
    //true - 遇到没有的属性就报错 false - 没有的属性不会管，不会报错
    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    //如果是空对象的时候,不抛异常  
    mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);  
    // 忽略 transient 修饰的属性
    mapper.configure(MapperFeature.PROPAGATE_TRANSIENT_MARKER, true);
    //修改序列化后日期格式
    mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);  
    mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
    //处理不同的时区偏移格式
    mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
    mapper.registerModule(new JavaTimeModule());
}

ObjectMapper mapper = new ObjectMapper();
String jsonString = "{\"name\":\"shawn\", \"age\":20}";
//将字符串转换为对象
Student student = mapper.readValue(jsonString, Student.class);
System.out.println(student);
//将对象转换为json字符串
jsonString = mapper.writeValueAsString(student);
System.out.println(jsonString);

//对象转为byte数组
byte[] byteArr = mapper.writeValueAsBytes(student);
System.out.println(byteArr);
//byte数组转为对象
Student student= mapper.readValue(byteArr, Student.class);
System.out.println(student);
结果：
[B@3327bd23
Student [ name: shawn, age: 20 ]

List<Student> studentList= new ArrayList<>();
studentList.add(new Student("shawn1" ,20 , new Date()));
studentList.add(new Student("shawn2" ,21 , new Date()));
studentList.add(new Student("shawn3" ,22 , new Date()));
studentList.add(new Student("shawn4" ,23 , new Date()));
 
String jsonStr = mapper.writeValueAsString(studentList);
System.out.println(jsonStr);
        
List<Student> studentList2 = mapper.readValue(jsonStr, List.class);
System.out.println("字符串转集合：" + studentList2 );
 

Map<String, Object> testMap = new HashMap<>();
testMap.put("name", "22");
testMap.put("age", 20);
testMap.put("date", new Date());
testMap.put("student", new Student("shawn", 20, new Date()));
 
 
String jsonStr = mapper.writeValueAsString(testMap);
System.out.println(jsonStr);
Map<String, Object> testMapDes = mapper.readValue(jsonStr, Map.class);
System.out.println(testMapDes);

// 修改时间格式
mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
Student student = new Student ("shawn",21, new Date());
student.setIntList(Arrays.asList(1, 2, 3));

String jsonStr = mapper.writeValueAsString(student);
System.out.println(jsonStr);

String test="{"results":[{"objectID":357,"geoPoints":[{"x":504604.59802246094,"y":305569.9150390625}]},{"objectID":358,"geoPoints":[{"x":504602.2680053711,"y":305554.43603515625}]}]}";
//此Json串比较复杂，包含了嵌套数组的形式，具有通用性。
//2.2.2.2实现反序列化
JsonNode node= objectMapper.readTree(test); //将Json串以树状结构读入内存
JsonNode contents=node.get("results");//得到results这个节点下的信息
//遍历results下的信息，size()函数可以得节点所包含的的信息的个数，类似于数组的长度
for(int i=0;i<contents.size();i++)  {
    //读取节点下的某个子节点的值
    System.out.println(contents.get(i).get("objectID").getIntValue());
    JsonNode geoNumber=contents.get(i).get("geoPoints");
    //循环遍历子节点下的信息
    for(int j=0;j<geoNumber.size();j++){
        System.out.println(geoNumber.get(j).get("x").getDoubleValue()+"  "+geoNumber.get(j).get("y").getDoubleValue());
    }
}

@Bean
public ObjectMapper objectMapper(){
    ObjectMapper objectMapper=new ObjectMapper();
    objectMapper.configure(SerializationFeature.WRITE_ENUMS_USING_INDEX,true);
    return objectMapper;
}

@Bean
public <T> RedisTemplate<String, T> redisTemplate(RedisConnectionFactory redisConnectionFactory) {
    RedisTemplate<String, T> redisTemplate = new RedisTemplate<>();
    redisTemplate.setConnectionFactory(redisConnectionFactory);
    Jackson2JsonRedisSerializer jackson2JsonRedisSerializer = new Jackson2JsonRedisSerializer(Object.class);
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.enable(DeserializationFeature.USE_LONG_FOR_INTS);
    //把类型信息作为属性写入Value
    objectMapper.activateDefaultTyping(objectMapper.getPolymorphicTypeValidator(), ObjectMapper.DefaultTyping.NON_FINAL);
    jackson2JsonRedisSerializer.setObjectMapper(objectMapper);
    redisTemplate.setKeySerializer(RedisSerializer.string());
    redisTemplate.setValueSerializer(jackson2JsonRedisSerializer);
    redisTemplate.setHashKeySerializer(RedisSerializer.string());
    redisTemplate.setHashValueSerializer(jackson2JsonRedisSerializer);
    redisTemplate.afterPropertiesSet();
    return redisTemplate;
}