文章目錄
ObjectMapper 是一個使用 Swift 編寫的用於 model 對象（類和結構體）和 JSON 之間轉換的框架。它提供一些功能將轉換成Java對象匹配JSON結構，反之亦然。它使用JsonParser和JsonGenerator的實例實現JSON實際的讀/寫。
記錄一些在工作中經常使用的方法。
maven 依賴
需要添加以下依賴：
<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>
使用場景
- Java對象轉換爲JSON對象
- JSON對象轉爲Java對象
- Java數組對象和JSON數組對象轉換
- 抽取json中的部分數據進行轉換
當我們請求別人的http接口時，有時候我們只需要返回的json的部分數據，可能嵌套的數據比較多，層級比較複雜，可以使用readTree(json);來獲取你需要的數據。
測試model類
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
*/
}
使用場景實例
1、Java對象轉換爲JSON對象
代碼：
@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);
}
運行結果：
{"id":"application_1574306678989_4374","user":"datadev","name":"pf_flink_server","state":"RUNNING"}
2、JSON對象轉換爲Java對象
代碼：
@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());
}
運行結果：
YarnAppModel{id='application_1574306678989_4374', user='datadev', name='pf_flink_server', state='RUNNING'}
3、Java數組對象和JSON數組對象轉換
代碼：
@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數組-->JSON數組
String json1 = mapper.writeValueAsString(lists);
System.out.println("數組轉JSON：\n"+json1);
System.out.println("-----------------------------------");
// JSON數組-->Java數組
List<YarnAppModel> lists2 = mapper.readValue(json1, new TypeReference<List<YarnAppModel>>(){});
System.out.println("JSON轉數組：\n"+lists2.toString());
}
運行結果:
數組轉JSON：
[{"id":"application_1574306678989_4374","user":"datadev","name":"pfflink","state":"RUNNING"},{"id":"application_1574306678989_4374_2","user":"datadev2","name":"pfflink2","state":"RUNNING"}]
-----------------------------------
JSON轉數組：
[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中的部分數據進行轉換
當我們請求別人的http接口時，有時候我們只需要返回的json的部分數據，可能嵌套的數據比較多，層級比較複雜，可以使用readTree(json);來獲取你需要的數據。
此時我們的model類裏面的字段應該是少於請求到的json數據的，並且數據層級比較複雜需要進一步提取，
如請求http後得到的返回值：
{"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}
]
}
}
我們需要的只是"app"下的數據並且不需要time字段的值，我們應該怎麼提取呢？
在提取之前我們需要做一些配置，不然會報一些異常（這些配置也不是全要配，配置項也不僅僅是這些）：
ObjectMapper objectMapper = new ObjectMapper();
//序列化的時候序列對象的所有屬性
objectMapper.setSerializationInclusion(Include.ALWAYS);
//反序列化的時候如果多了其他屬性,不拋出異常
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
//如果是空對象的時候,不拋異常
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
//取消時間的轉化格式,默認是時間戳,可以取消,同時需要設置要表現的時間格式
objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"))
代碼：
@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數據：\n"+json);
ObjectMapper mapper = new ObjectMapper();
// 轉換爲格式化的json
mapper.enable(SerializationFeature.INDENT_OUTPUT);
// 如果json中有新增的字段並且是實體類類中不存在的，不報錯
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
// ObjectMapper讀取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("提取結果：");
for (YarnAppModel yarnAppModel : resoult) {
System.out.println(yarnAppModel.getId()+"\t"+yarnAppModel.getName()+"\t"+yarnAppModel.getState());
}
}
運行結果：
HTTP返回json數據：
{"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}]}}
提取結果：
application_1574306678989_4623 wordcount RUNNING
application_1574306678989_4543 wordcount RUNNING