在Java REST中解析JSON参数时出错

Question

I have recently upgraded my REST API to use jersey 2.x and now I am unable to retrieve JSON body params the way I used to, the methods simply do not get called anymore. My guess is I'm missing a dependency to parse the JSON to a java object but I'm not too sure what i need to add in, any help appreciated.

pom.xml

<dependencies>
    <dependency>
        <groupId>javax.ws.rs</groupId>
        <artifactId>javax.ws.rs-api</artifactId>
        <version>2.0.1</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <artifactId>jersey-container-servlet</artifactId>
        <version>2.19</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-server</artifactId>
        <version>2.19</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-client</artifactId>
        <version>2.19</version>
    </dependency>
    <dependency>
        <groupId>com.googlecode.json-simple</groupId>
        <artifactId>json-simple</artifactId>
        <version>1.1.1</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-multipart</artifactId>
        <version>2.22</version>
    </dependency>
</dependencies>

REST method

@POST
    @Path("/users/{userId}/friends")
    @Produces(MediaType.APPLICATION_JSON)
    @Consumes(MediaType.APPLICATION_JSON)
    public Response followUser(@PathParam("userId") Integer myUserId, FollowUserBean user) {}

FollowUserBean.java

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class FollowUserBean {
    public Integer friendId;

    public FollowUserBean() {}
}

Answer 1

You need a JSON provider

At time of writing, Jersey 2.x integrates with the following modules to provide JSON support:

• MOXy
• Java API for JSON Processing (JSON-P)
• Jackson
• Jettison

Using Jackson

See below the steps required to use Jackson as a JSON provider for Jersey 2.x:

Adding Jackson module dependencies

To use Jackson 2.x as your JSON provider you need to add jersey-media-json-jackson module to your pom.xml file:

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-jackson</artifactId>
    <version>2.25.1</version>
</dependency>

To use Jackson 1.x it'll look like:

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-jackson1</artifactId>
    <version>2.25.1</version>
</dependency>

Registering Jackson module

Besides adding the dependency mentioned above, you need to register JacksonFeature (or Jackson1Feature for Jackson 1.x) in your Application / ResourceConfig subclass:

@ApplicationPath("/api")
public class MyApplication extends Application {

    @Override
    public Set<Class<?>> getClasses() {
        Set<Class<?>> classes = new HashSet<Class<?>>();
        classes.add(JacksonFeature.class);
        return classes;
    }
}

@ApplicationPath("/api")
public class MyApplication extends ResourceConfig {

    public MyApplication() {
        register(JacksonFeature.class);
    }
}

If you don't have an Application / ResourceConfig subclass, you can register the JacksonFeature in your web.xml deployment descriptor. The specific resource, provider and feature fully-qualified class names can be provided in a comma-separated value of jersey.config.server.provider.classnames initialization parameter.

<init-param>
    <param-name>jersey.config.server.provider.classnames</param-name>
    <param-value>org.glassfish.jersey.jackson.JacksonFeature</param-value>
</init-param>

The MessageBodyWriter provided by Jackson is JacksonJsonProvider .

---

For more details, check the Jersey documentation about support for common media type representations.

Answer 2

You may be missing Jersey JSON Jackson (2.x) entity providers support module:

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-jackson</artifactId>
    <version>2.19</version>
    <scope>compile</scope>
</dependency>

It is recommended to use the same Jersey version in all libs.