文章目录
ObjectMapper 是一个使用 Swift 编写的用于 model 对象（类和结构体）和 JSON 之间转换的框架。它提供一些功能将转换成Java对象匹配JSON结构，反之亦然。它使用JsonParser和JsonGenerator的实例实现JSON实际的读/写。
记录一些在工作中经常使用的方法。
maven 依赖
需要添加以下依赖：
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.5</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.9.5</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>2.9.5</version>
</dependency>
使用场景
- Java对象转换为JSON对象
- JSON对象转为Java对象
- Java数组对象和JSON数组对象转换
- 抽取json中的部分数据进行转换
当我们请求别人的http接口时，有时候我们只需要返回的json的部分数据，可能嵌套的数据比较多，层级比较复杂，可以使用readTree(json);来获取你需要的数据。
测试model类
package com.qunar.pf.flink.server.model;
/** @Description: @Author: renxin.tang @Date: 2019/11/21 21:48 */
public class YarnAppModel {
private String id;
private String user;
private String name;
private String state;
/*
getter and setter and toString
*/
}
使用场景实例
1、Java对象转换为JSON对象
代码：
@Test
public void javaObjectToJson() throws JsonProcessingException {
YarnAppModel yarnAppModel = new YarnAppModel();
yarnAppModel.setId("application_1574306678989_4374");
yarnAppModel.setName("pf_flink_server");
yarnAppModel.setUser("datadev");
yarnAppModel.setState("RUNNING");
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(yarnAppModel);
System.out.println(json);
}
运行结果：
{"id":"application_1574306678989_4374","user":"datadev","name":"pf_flink_server","state":"RUNNING"}
2、JSON对象转换为Java对象
代码：
@Test
public void jsonToJavaObject() throws IOException {
String json = "{\"id\":\"application_1574306678989_4374\",\"user\":\"datadev\",\"name\":\"pf_flink_server\",\"state\":\"RUNNING\"}";
ObjectMapper mapper = new ObjectMapper();
YarnAppModel yarnAppModel = mapper.readValue(json, YarnAppModel.class);
System.out.println(yarnAppModel.toString());
}
运行结果：
YarnAppModel{id='application_1574306678989_4374', user='datadev', name='pf_flink_server', state='RUNNING'}
3、Java数组对象和JSON数组对象转换
代码：
@Test
public void jsonCollectorAndJavaColletor() throws IOException {
ObjectMapper mapper = new ObjectMapper();
YarnAppModel yarnAppModel = new YarnAppModel("application_1574306678989_4374","datadev","pfflink","RUNNING");
YarnAppModel yarnAppModel2 = new YarnAppModel("application_1574306678989_4374_2","datadev2","pfflink2","RUNNING");
List<YarnAppModel> lists = new ArrayList<>();
lists.add(yarnAppModel);
lists.add(yarnAppModel2);
// Java数组-->JSON数组
String json1 = mapper.writeValueAsString(lists);
System.out.println("数组转JSON：\n"+json1);
System.out.println("-----------------------------------");
// JSON数组-->Java数组
List<YarnAppModel> lists2 = mapper.readValue(json1, new TypeReference<List<YarnAppModel>>(){});
System.out.println("JSON转数组：\n"+lists2.toString());
}
运行结果:
数组转JSON：
[{"id":"application_1574306678989_4374","user":"datadev","name":"pfflink","state":"RUNNING"},{"id":"application_1574306678989_4374_2","user":"datadev2","name":"pfflink2","state":"RUNNING"}]
-----------------------------------
JSON转数组：
[YarnAppModel{id='application_1574306678989_4374', user='datadev', name='pfflink', state='RUNNING'}, YarnAppModel{id='application_1574306678989_4374_2', user='datadev2', name='pfflink2', state='RUNNING'}]
4、抽取json中的部分数据进行转换
当我们请求别人的http接口时，有时候我们只需要返回的json的部分数据，可能嵌套的数据比较多，层级比较复杂，可以使用readTree(json);来获取你需要的数据。
此时我们的model类里面的字段应该是少于请求到的json数据的，并且数据层级比较复杂需要进一步提取，
如请求http后得到的返回值：
{"apps":
{"app":[
{"id":"application_1574306678989_4623","user":"datadev","name":"wordcount","state":"RUN","time":15432523535255},
{"id":"application_1574306678989_4543","user":"datadev2","name":"wordcount","state":"RUN","time":15432523535255}
]
}
}
我们需要的只是"app"下的数据并且不需要time字段的值，我们应该怎么提取呢？
在提取之前我们需要做一些配置，不然会报一些异常（这些配置也不是全要配，配置项也不仅仅是这些）：
ObjectMapper objectMapper = new ObjectMapper();
//序列化的时候序列对象的所有属性
objectMapper.setSerializationInclusion(Include.ALWAYS);
//反序列化的时候如果多了其他属性,不抛出异常
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
//如果是空对象的时候,不抛异常
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
//取消时间的转化格式,默认是时间戳,可以取消,同时需要设置要表现的时间格式
objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"))
代码：
@Test
public void getYarnApps() throws IOException {
String path ="http://xxxxxxx:8088/ws/v1/cluster/apps";
String json = HttpUtil.doGet(path,null);
System.out.println("HTTP返回json数据：\n"+json);
ObjectMapper mapper = new ObjectMapper();
// 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);
// ObjectMapper读取json文件
JsonNode root = mapper.readTree(json);
JsonNode apps = root.get("apps");
JsonNode app = apps.get("app");
List<YarnAppModel> resoult = mapper.readValue(app.toString(), new TypeReference<List<YarnAppModel>>(){});
System.out.println("提取结果：");
for (YarnAppModel yarnAppModel : resoult) {
System.out.println(yarnAppModel.getId()+"\t"+yarnAppModel.getName()+"\t"+yarnAppModel.getState());
}
}
运行结果：
HTTP返回json数据：
{"apps":{"app":[{"id":"application_1574306678989_4623","user":"datadev","name":"wordcount","state":"RUNNING","time":15432523535255},{"id":"application_1574306678989_4543","user":"datadev2","name":"wordcount","state":"RUNNING","time":15432523535255}]}}
提取结果：
application_1574306678989_4623 wordcount RUNNING
application_1574306678989_4543 wordcount RUNNING