ObjectMapper 对于JSON与Java对象之间的转换使用

向右看齐 2022-02-19 19:06 515阅读 0赞

在项目中使用到了ObjectMapper，故研究了一下。现将自己的几个测试用例和大家分享一下~

首先在pom.xml文件中，加入依赖：

<dependency>
                <groupId>com.fasterxml.jackson.core</groupId>
                <artifactId>jackson-databind</artifactId>
                <version>2.8.3</version>
            </dependency>

创建一个实体类XwjUser：

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public class XwjUser implements Serializable {
    
        private static final long serialVersionUID = 1L;
    
        private int id;
    
        private String message;
    
        private Date sendTime;
    
        // 这里手写字母大写，只是为了测试使用，是不符合java规范的
        private String NodeName;
    
        private List<Integer> intList;
    
        public XwjUser() {
            super();
        }
    
        public XwjUser(int id, String message, Date sendTime) {
            super();
            this.id = id;
            this.message = message;
            this.sendTime = sendTime;
        }
    
        public int getId() {
            return id;
        }
    
        public void setId(int id) {
            this.id = id;
        }
    
        public String getMessage() {
            return message;
        }
    
        public void setMessage(String message) {
            this.message = message;
        }
    
        public Date getSendTime() {
            return sendTime;
        }
    
        public void setSendTime(Date sendTime) {
            this.sendTime = sendTime;
        }
    
        public String getNodeName() {
            return NodeName;
        }
    
        public void setNodeName(String nodeName) {
            NodeName = nodeName;
        }
    
        public List<Integer> getIntList() {
            return intList;
        }
    
        public void setIntList(List<Integer> intList) {
            this.intList = intList;
        }
    
        @Override
        public String toString() {
            return "XwjUser [id=" + id + ", message=" + message + ", sendTime=" + sendTime + ", intList=" + intList + "]";
        }
    
    }

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先创建一个ObjectMapper，然后赋值一些属性：

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public static ObjectMapper mapper = new ObjectMapper();
    
    static {
        // 转换为格式化的json
        mapper.enable(SerializationFeature.INDENT_OUTPUT);
    
        // 如果json中有新增的字段并且是实体类类中不存在的，不报错
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    }

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1、对象与json字符串、byte数组

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@Test
        public void testObj() throws JsonGenerationException, JsonMappingException, IOException {
            XwjUser user = new XwjUser(1, "Hello World", new Date());
    
            mapper.writeValue(new File("D:/test.txt"), user); // 写到文件中
            // mapper.writeValue(System.out, user); //写到控制台
    
            String jsonStr = mapper.writeValueAsString(user);
            System.out.println("对象转为字符串：" + jsonStr);
    
            byte[] byteArr = mapper.writeValueAsBytes(user);
            System.out.println("对象转为byte数组：" + byteArr);
    
            XwjUser userDe = mapper.readValue(jsonStr, XwjUser.class);
            System.out.println("json字符串转为对象：" + userDe);
    
            XwjUser useDe2 = mapper.readValue(byteArr, XwjUser.class);
            System.out.println("byte数组转为对象：" + useDe2);
        }

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运行结果：

![复制代码][copycode.gif]

对象转为字符串：{
      "id" : 1,
      "message" : "Hello World",
      "sendTime" : 1525163446305,
      "intList" : null,
      "nodeName" : null
    }
    对象转为byte数组：[B@3327bd23
    json字符串转为对象：XwjUser [id=1, message=Hello World, sendTime=Tue May 01 16:30:46 CST 2018, intList=null]
    byte数组转为对象：XwjUser [id=1, message=Hello World, sendTime=Tue May 01 16:30:46 CST 2018, intList=null]

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注意，对象转json字符串时，对象中的NodeName首字母是大写，转出来是小写

2、list集合与json字符串

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@Test
        public void testList() throws JsonGenerationException, JsonMappingException, IOException {
            List<XwjUser> userList = new ArrayList<>();
            userList.add(new XwjUser(1, "aaa", new Date()));
            userList.add(new XwjUser(2, "bbb", new Date()));
            userList.add(new XwjUser(3, "ccc", new Date()));
            userList.add(new XwjUser(4, "ddd", new Date()));
    
            String jsonStr = mapper.writeValueAsString(userList);
            System.out.println("集合转为字符串：" + jsonStr);
            
            List<XwjUser> userListDes = mapper.readValue(jsonStr, List.class);
            System.out.println("字符串转集合：" + userListDes);
        }

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运行结果：

![复制代码][copycode.gif]

集合转为字符串：[ {
      "id" : 1,
      "message" : "aaa",
      "sendTime" : 1525164096846,
      "intList" : null,
      "nodeName" : null
    }, {
      "id" : 2,
      "message" : "bbb",
      "sendTime" : 1525164096846,
      "intList" : null,
      "nodeName" : null
    }, {
      "id" : 3,
      "message" : "ccc",
      "sendTime" : 1525164096846,
      "intList" : null,
      "nodeName" : null
    }, {
      "id" : 4,
      "message" : "ddd",
      "sendTime" : 1525164096846,
      "intList" : null,
      "nodeName" : null
    } ]
    字符串转集合：[{id=1, message=aaa, sendTime=1525164096846, intList=null, nodeName=null}, {id=2, message=bbb, sendTime=1525164096846, intList=null, nodeName=null}, {id=3, message=ccc, sendTime=1525164096846, intList=null, nodeName=null}, {id=4, message=ddd, sendTime=1525164096846, intList=null, nodeName=null}]

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3、map与json字符串

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@SuppressWarnings("unchecked")
        @Test
        public void testMap() {
            Map<String, Object> testMap = new HashMap<>();
            testMap.put("name", "merry");
            testMap.put("age", 30);
            testMap.put("date", new Date());
            testMap.put("user", new XwjUser(1, "Hello World", new Date()));
    
            try {
                String jsonStr = mapper.writeValueAsString(testMap);
                System.out.println("Map转为字符串：" + jsonStr);
                try {
                    Map<String, Object> testMapDes = mapper.readValue(jsonStr, Map.class);
                    System.out.println("字符串转Map：" + testMapDes);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
        }

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运行结果：

![复制代码][copycode.gif]

Map转为字符串：{
      "date" : 1525164199804,
      "name" : "merry",
      "user" : {
        "id" : 1,
        "message" : "Hello World",
        "sendTime" : 1525164199805,
        "intList" : null,
        "nodeName" : null
      },
      "age" : 30
    }
    字符串转Map：{date=1525164199804, name=merry, user={id=1, message=Hello World, sendTime=1525164199805, intList=null, nodeName=null}, age=30}

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4、修改转换时的日期格式：

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@Test
        public void testOther() throws IOException {
            // 修改时间格式
            mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
            XwjUser user = new XwjUser(1, "Hello World", new Date());
            user.setIntList(Arrays.asList(1, 2, 3));
    
            String jsonStr = mapper.writeValueAsString(user);
            System.out.println("对象转为字符串：" + jsonStr);
        }

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运行结果：

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对象转为字符串：{
      "id" : 1,
      "message" : "Hello World",
      "sendTime" : "2018-05-01 16:44:06",
      "intList" : [ 1, 2, 3 ],
      "nodeName" : null
    }

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[copycode.gif]: /images/20220219/4515cf4f159546cdaae7cf2ca9db19ae.png