使用ObjectMapper转换JSON

本是古典何须时尚 2023-06-15 09:59 9阅读 0赞

### 文章目录 ###

*  maven 依赖
 *  使用场景
 *  测试model类
 *  使用场景实例
 *   *  1、Java对象转换为JSON对象
     *  2、JSON对象转换为Java对象
     *  3、Java数组对象和JSON数组对象转换
     *  4、抽取json中的部分数据进行转换

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>
    
    
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.9.5</version>
    </dependency>
    
    
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.9.5</version>
    </dependency>

# 使用场景 #

1.  Java对象转换为JSON对象
2.  JSON对象转为Java对象
3.  Java数组对象和JSON数组对象转换
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。

# 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