JAX-RS客户端对Java8日期/时间进行Jackson（反）序列化

Question

我正在为REST端点创建一个服务客户端，将JAX-RS客户端用于HTTP请求，并使用Jackson来（反）序列化JSON实体。为了处理JSR-310（Java8）日期/时间对象，我将该com.fasterxml.jackson.datatype:jackson-datatype-jsr310模块作为对服务客户端的依赖项添加，但是我没有使它起作用。

如何配置JAX-RS和/或Jackson使用jsr310模块？

我使用以下依赖项：

<dependency>
  <groupId>javax.ws.rs</groupId>
  <artifactId>javax.ws.rs-api</artifactId>
  <version>${jax-rs.version}</version>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-annotations</artifactId>
  <version>${jackson.version}</version>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.datatype</groupId>
  <artifactId>jackson-datatype-jsr310</artifactId>
  <version>${jackson.version}</version>
</dependency>

我不想使服务客户端（以库形式发布）依赖于任何特定的实现（例如Jersey），因此我仅依赖于JAX-RS API。为了运行集成测试，我添加了：

<dependency>
  <groupId>org.glassfish.jersey.core</groupId>
  <artifactId>jersey-client</artifactId>
  <version>${jersey.version}</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.glassfish.jersey.inject</groupId>
  <artifactId>jersey-hk2</artifactId>
  <version>${jersey.version}</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.glassfish.jersey.media</groupId>
  <artifactId>jersey-media-json-jackson</artifactId>
  <version>${jersey.version}</version>
  <scope>test</scope>
</dependency>

JAX-RS客户端的实例化是在工厂对象中完成的，如下所示：

import javax.ws.rs.Produces;
import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;

@Produces
public Client produceClient() {
    return ClientBuilder.newClient();
}

典型的DTO如下所示：

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

import java.time.Instant;

import static java.util.Objects.requireNonNull;

@JsonPropertyOrder({"n", "t"})
public final class Message {

    private final String name;
    private final Instant timestamp;

    @JsonCreator
    public Message(@JsonProperty("n") final String name,
                   @JsonProperty("t") final Instant timestamp) {
        this.name = requireNonNull(name);
        this.timestamp = requireNonNull(timestamp);
    }

    @JsonProperty("n")
    public String getName() {
        return this.name;
    }

    @JsonProperty("t")
    public Instant getTimestamp() {
        return this.timestamp;
    }

    // equals(Object), hashCode() and toString()
}

请求是这样完成的：

import javax.ws.rs.client.Entity;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.MediaType;

public final class Gateway {

    private final WebTarget endpoint;

    public Message postSomething(final Something something) {
        return this.endpoint
                .request(MediaType.APPLICATION_JSON_TYPE)
                .post(Entity.json(something), Message.class);
    }

    // where Message is the class defined above and Something is a similar DTO
}

JSON序列化和反序列化对于Strings，int，BigIntegers，Lists等都可以正常工作。但是，当我System.out.println(gateway.postSomthing(new Something("x", "y"));在测试中执行类似操作时，会出现以下异常：

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `java.time.Instant` (no Creators, like default construct, exist): no String-argument constructor/factory method to deserialize from String value ('Fri, 22 Sep 2017 10:26:52 GMT')
 at [Source: (org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream); line: 1, column: 562] (through reference chain: Message["t"])
        at org.example.com.ServiceClientTest.test(ServiceClientTest.java:52)
Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException:
Cannot construct instance of `java.time.Instant` (no Creators, like default construct, exist): no String-argument constructor/factory method to deserialize from String value ('Fri, 22 Sep 2017 10:26:52 GMT')
 at [Source: (org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream); line: 1, column: 562] (through reference chain: Message["t"])
        at org.example.com.ServiceClientTest.test(ServiceClientTest.java:52)

从中可以得出结论，杰克逊不知道如何将字符串反序列化为Instants。我找到了有关此主题的博客和SO问题，但没有找到有关如何使其工作的明确解释。

请注意，我希望服务客户端像"Fri, 22 Sep 2017 10:26:52 GMT"和一样处理日期字符串"2017-09-22T10:26:52.123Z"，但我希望它始终序列化为ISO 8601日期字符串。

谁能解释如何将反序列化变为Instant作品？

Answer 1

在示例代码中，您目前依赖 jersey-media-json-jackson。您可能会更好地依赖 Jackson 的 JAX-RS JSON，因为您可以使用标准 JAX-RS API（当然还有 Jackson API）配置 Jackson 映射器。

    <dependency>
        <groupId>com.fasterxml.jackson.jaxrs</groupId>
        <artifactId>jackson-jaxrs-json-provider</artifactId>
        <version>${jackson.version}</version>
    </dependency>

删除 jersey-media-json-jackson 并添加 jackson-jaxrs-json-provider 依赖项后，您可以配置 JacksonJaxbJsonProvider 并将其注册到生成客户端的类中：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import com.fasterxml.jackson.jaxrs.json.JacksonJaxbJsonProvider;
import com.fasterxml.jackson.jaxrs.json.JacksonJsonProvider;

import javax.ws.rs.Produces;
import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;

import static com.fasterxml.jackson.jaxrs.json.JacksonJaxbJsonProvider.DEFAULT_ANNOTATIONS;

public class ClientProducer {

    private JacksonJsonProvider jsonProvider;

    public ClientProducer() {
        // Create an ObjectMapper to be used for (de)serializing to/from JSON.
        ObjectMapper objectMapper = new ObjectMapper();
        // Register the JavaTimeModule for JSR-310 DateTime (de)serialization
        objectMapper.registerModule(new JavaTimeModule());
        // Configure the object mapper te serialize to timestamp strings.
        objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        // Create a Jackson Provider
        this.jsonProvider = new JacksonJaxbJsonProvider(objectMapper, DEFAULT_ANNOTATIONS);
    }

    @Produces
    public Client produceClient() {

        return ClientBuilder.newClient()
                // Register the jsonProvider
                .register(this.jsonProvider);
    }
}

希望这可以帮助。