Java 使用Jongo和Jackson 2，如何将MongoDB对象id（在POJO中以字符串_id表示）反序列化为十六进制字符串表示？

我使用最新版本的MongoDB数据库和最新版本的官方JAVA MongoDB驱动程序

我在pom.xml中使用的依赖项：

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>

        ...

        <jersey.container.version>2.13</jersey.container.version>
        <jackson.version>2.4.3</jackson.version>
        <genson.version>1.1</genson.version>        
        <jongo.version>1.1</jongo.version>
    </properties>

  <dependencies>

     ...

    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-servlet</artifactId>
        <version>${jersey.container.version}</version>
    </dependency>

    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-json-jackson</artifactId>
        <version>${jersey.container.version}</version>
    </dependency>

    <!-- Required only when you are using JAX-RS Client -->
    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-client</artifactId>
        <version>${jersey.container.version}</version>
    </dependency>

    <dependency>
        <groupId>javax.ws.rs</groupId>
        <artifactId>javax.ws.rs-api</artifactId>
        <version>2.0.1</version>
    </dependency>

    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-multipart</artifactId>
        <version>2.13</version>
    </dependency>

    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>${jackson.version}</version>
    </dependency>

    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>${jackson.version}</version>
    </dependency>

    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>${jackson.version}</version>
    </dependency>

    <dependency>
        <groupId>org.jongo</groupId>
        <artifactId>jongo</artifactId>
        <version>${jongo.version}</version>
    </dependency>

    <dependency>
        <groupId>org.mongodb</groupId>
        <artifactId>mongo-java-driver</artifactId>
        <version>2.12.3</version>
    </dependency>
  </dependencies>

我的web服务：

import javax.ws.rs.Consumes;
import javax.ws.rs.DELETE;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.PUT;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;

import com.hive5.dao.UsersDAO;
import com.hive5.enums.CustomHttpResponse;
import com.hive5.pojo.User;

@Path("/v1")
public class V1_Users {

    @GET
    @Path("/users/{firstName}")
    @Produces(MediaType.APPLICATION_JSON)
    public Response getUser(@PathParam("firstName") String firstName) {
        if (firstName != null && !firstName.trim().isEmpty()) {
            Response response = UsersDAO.getUser(firstName);
            return response;
        } else {
            return Response
                    .status(CustomHttpResponse.REQUEST_NOT_ACCEPTABLE
                            .getStatusCode())
                    .entity(CustomHttpResponse.REQUEST_NOT_ACCEPTABLE
                            .getStatusMessage()).build();
        }
    }

    ...

}

我的刀：

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.ws.rs.core.Response;

import org.apache.log4j.Logger;
import org.bson.types.ObjectId;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.hive5.enums.CustomHttpResponse;
import com.hive5.pojo.User;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;
import com.mongodb.MongoException;

public class UsersDAO {

    ...

    public static Response getUser(String firstName) {
        DB db = MONGO_CLIENT.getDB(DATABASE_NAME);
        DBCollection collection = db.getCollection("users");
        BasicDBObject whereQuery = new BasicDBObject();
        whereQuery.put("firstName", firstName);

        DBCursor cursor = null;
        DBObject dbObject = null;
        User user = null;

        ObjectMapper mapper = new ObjectMapper();

        CustomHttpResponse customHttpResponse = CustomHttpResponse.OK;

        try {
            cursor = collection.find(whereQuery).limit(1);
            if (cursor.count() > 0) {
                dbObject = cursor.next();
                user = mapper.readValue(dbObject.toString(), User.class);
            } else {
                // User Not Found
                customHttpResponse = CustomHttpResponse.NOT_FOUND_CUSTOM;
                customHttpResponse
                        .formatStatusMessagePatternWithArguments(firstName);
            }
        } catch (MongoException | IOException e) {
            customHttpResponse = CustomHttpResponse.INTERNAL_SERVER_ERROR;
            LOG_TO_CONSOLE.fatal(e, e);
            LOG_TO_FILE.fatal(e, e);
        } finally {
            if (customHttpResponse == CustomHttpResponse.OK
                    || customHttpResponse == CustomHttpResponse.NOT_FOUND_CUSTOM) {
                LOG_TO_CONSOLE.debug(customHttpResponse.toString());
            }
        }

        Response response = null;
        switch (customHttpResponse) {
        case OK:

            System.out.println("user.get_id() -> " + user.get_id());

            response = Response.status(customHttpResponse.getStatusCode())
                    .entity(user).build();
            break;
        default:
            response = Response.status(customHttpResponse.getStatusCode())
                    .entity(customHttpResponse.getStatusMessage()).build();
            break;
        }

        return response;
    }

    ...
}

tomcat web服务器控制台中显示的输出（在请求了上面的web服务之后，请参阅上面的我的DAO类和getUser（String firstName）{…}方法）：

使用POSTMAN请求web服务后得到的JSON结果：

{
    "firstName": "Yolo",
    "lastName": "DOUCE",
    "age": 31,
    "_id": {
        "new": false,
        "inc": -2041720087,
        "machine": -1473854181,
        "timeSecond": 1413818742,
        "timestamp": 1413818742,
        "time": 1413818742000,
        "date": 1413818742000
    }
}

正如您所看到的，_id字段不是十六进制字符串格式，而是有多个字段，这不是我所期望的

1-实际上，在我的DAO中，我能够打印此字段的十六进制字符串格式，因此我不明白为什么在我的web服务中，它返回一个显然包含字符串id对象表示形式的响应？

2-我的第二个问题是，在我的特殊情况下，如何使用jongo和/或jackson Quicker xml V2和MongoDB反序列化为JSON并返回字符串id（位于我的用户POJO中的字段）的十六进制字符串表示形式？

始终使用@ObjectId将属性映射到ObjectId的新实例。将此属性映射到字符串时，这是错误的

为了避免这种行为，我们可以使用以下自定义JSON序列化程序类（最初由某个用户1878815提供）NoObjectIdSerializer，我对其进行了一些修改：

import java.io.IOException;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

public class NoObjectIdSerializer extends JsonSerializer<String> {

    @Override
    public void serialize(String value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        if(value == null){
            jgen.writeNull();
        }else{
            jgen.writeString(value);
        }
    }

}

有

这个答案是基于之前的答案提供的，非常感谢他

另外，要获得更详细的解释，请遵循以下步骤

{
    "firstName": "Yolo",
    "lastName": "DOUCE",
    "age": 31,
    "_id": {
        "new": false,
        "inc": -2041720087,
        "machine": -1473854181,
        "timeSecond": 1413818742,
        "timestamp": 1413818742,
        "time": 1413818742000,
        "date": 1413818742000
    }
}

import java.io.IOException;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

public class NoObjectIdSerializer extends JsonSerializer<String> {

    @Override
    public void serialize(String value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
        if(value == null){
            jgen.writeNull();
        }else{
            jgen.writeString(value);
        }
    }

}

import org.jongo.marshall.jackson.oid.ObjectId;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.mypackage.NoObjectIdSerializer;

import com.google.common.base.MoreObjects;
import java.util.Objects;

public class User {

   @ObjectId
   @JsonSerialize(using = NoObjectIdSerializer.class)
   protected final String _id;

   ...
}