使用objectMapper处理数据之间的转化详解

本文主要是介绍使用objectMapper处理数据之间的转化详解，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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：

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;}@Overridepublic String toString() {return "XwjUser [id=" + id + ", message=" + message + ", sendTime=" + sendTime + ", intList=" + intList + "]";}}

先创建一个ObjectMapper，然后赋值一些属性：

public static ObjectMapper mapper = new ObjectMapper();static {// 转换为格式化的jsonmapper.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);
}

1、对象与json字符串、byte数组

@Testpublic 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);}

运行结果：

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]

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

@Testpublic 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);}

运行结果：

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}]

3、map与json字符串

@SuppressWarnings("unchecked")@Testpublic 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();}}

运行结果：

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}

4、修改转换时的日期格式：

@Testpublic 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);}

运行结果：

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
}

原文链接：https://www.cnblogs.com/xuwenjin/p/8976696.html

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