json rootelement 在 JSON 响应中显示 ArrayList 而不是 @JsonRootName("TestClass") 作为根元素

Question

我正在开发 maven SpringBoot 微服务应用程序，我希望 json 字符串带有我提到的根元素，但它给了我带有 ArrayList 作为根元素的 json 字符串。

报告了很多类似的问题，但没有一个解决方案适合我。

预计是

{
    "TestClass": [
        {
            "itemId": "000023",
            "owner": "XYZ",
            "name": "BMW"
        },
        {
            "itemId": "000022",
            "owner": "PQR",
            "name": "GM"
        },
        {
            "itemId": "000021",
            "owner": "xyz",
            "name": "Ford"
        }
    ]
}

实际的 json 响应看起来像

{
    "ArrayList": [
        {
            "itemId": "000023",
            "owner": "XYZ",
            "name": "BMW"
        },
        {
            "itemId": "000022",
            "owner": "PQR",
            "name": "GM"
        },
        {
            "itemId": "000021",
            "owner": "xyz",
            "name": "Ford"
        }
    ]
}

POJO 模型类

import com.fasterxml.jackson.annotation.JsonRootName;

@JsonRootName("TestClass")
public class TestClass {

    private String itemId;

    private String owner;

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getItemId() {
        return itemId;
    }

    public void setItemId(String itemId) {
        this.itemId = itemId;
    }

    public String getOwner() {
        return owner;
    }

    public void setOwner(String owner) {
        this.owner = owner;
    }
}


package com.apps.partnerecosystem.rest;

import java.util.ArrayList;
import java.util.List;

import javax.inject.Named;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;

import com.teamcenter.hello.Hello;

@Named
@Path("/")
public class TestClassRest {

    private static List<TestClass> clients = new ArrayList<TestClass>();

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public List<TestClass> getClientes() {
        return clients;
    }


    @GET
    @Path("list")
    @Produces(MediaType.APPLICATION_JSON)
    public List<TestClass> getList() {
        List<TestClass> list = new ArrayList<TestClass>();
        TestClassitem1 = new TestClass();
        item1.setItemId("Test");
        item1.setOwner("deshpapr");
        item1.setName("Test");
        list.add(item1);
        list.add(item1);
        return list;
    }
}

应用配置文件

package com.apps.partnerecosystem.comappspartnerecosystem;

import javax.inject.Named;

import org.glassfish.jersey.server.ResourceConfig;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.SerializationFeature;

@Configuration
public class ApplicationConfig {

    @Named
    static class JerseyConfig extends ResourceConfig {
        public JerseyConfig() {
            this.packages("com.apps.partnerecosystem.rest");
        }
    }

    @Bean
    public Jackson2ObjectMapperBuilder jacksonBuilder() {
        Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
        builder.featuresToEnable(SerializationFeature.WRAP_ROOT_VALUE); // enables
                                                                        // wrapping
                                                                        // for
                                                                        // root
                                                                        // elements
       builder.featuresToEnable(DeserializationFeature.UNWRAP_ROOT_VALUE);
        return builder;
    }
    /*
     * public RestTemplate restTemplate() { RestTemplate restTemplate = new
     * RestTemplate(); restTemplate. return restTemplate; }
     */
}

Answer 1

试试下面的代码。

package com.learn.jackson;

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public class JacksonConvertList {

    public static void main(String[] args) throws Exception {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.enable(SerializationFeature.INDENT_OUTPUT);
        objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
        // Define map which will be converted to JSON

        List<TestClass> list = Stream.of(new TestClass("item1", "owner1", "name1"), new TestClass("item2", "owner1", "name2"),
                new TestClass("item3", "owner1", "name3"), new TestClass("item4", "owner1", "name4")).collect(Collectors.toList());

        // option 1: Use a collection wrapper class as below. 
        TestClassCollection collection = new TestClassCollection(list);
        String arrayToJson = objectMapper.writeValueAsString(collection);

        // option 2: Use Map instead of List.
//      Map<String, List<TestClass>> map = new HashMap<>();
//      map.put(TestClass.class.getSimpleName(), list);
//      String arrayToJson = objectMapper.writeValueAsString(map);

        System.out.println(arrayToJson);

    }

}

# Add this constructor to your class
public TestClass(String itemId, String owner, String name) {
        this.itemId = itemId;
        this.owner = owner;
        this.name = name;
    }

# Add TestClassCollection class 
package com.learn.jackson;

import java.util.List;
import com.fasterxml.jackson.annotation.JsonProperty;

public class TestClassCollection {

    @JsonProperty("TestClass")
    private List<TestClass> testClass;

    public TestClassCollection (List<TestClass> testClass) {
        this.testClass = testClass;
    }

}

使用任一选项输出：

{
  "TestClass" : [ {
    "itemId" : "item1",
    "owner" : "owner1",
    "name" : "name1"
  }, {
    "itemId" : "item2",
    "owner" : "owner1",
    "name" : "name2"
  }, {
    "itemId" : "item3",
    "owner" : "owner1",
    "name" : "name3"
  }, {
    "itemId" : "item4",
    "owner" : "owner1",
    "name" : "name4"
  } ]
}

另一种选择是： 只需使用 ObjectWriter withRootName 方法。但是，这对于转换为 json 很有用。在阅读时，您将再次需要自定义阅读来列出。

即使用以下内容，而不在您的原始代码中设置 SerializationFeature.WRAP_ROOT_VALUE 和 DeserializationFeature.UNWRAP_ROOT_VALUE。

objectMapper.writer().withRootName(TestClass.class.getSimpleName()).writeValueAsString(list);