AWS Lambda in Java: how to call a REST endpoint exposed in API Gateway

Question

I have a REST API exposed on the AWS infrastructure on the behalf of API Gateway. In a Lambda function in Java I need to call the associated endpoints. The AWS documentation recommends to generate a client using the API Gateway console. However, the generated client has several dozens of classes, perhaps even 100 ! Of course, this couldn't be the way.

Did anyone succeed to call API Gateway exposed endpoints using RESTeasy or CXF clients ? Or even Apache HTTP Client ?

Many thanks in advance.

Answer 1

I'm answering my own question. Finally, I confirm that using JAX-RS clients works as expected with API Gateway. In my case, I preferred RESTeasy, but it should work with CXF as well or even with the Apache HTTp Client. Here is what I did:

Maven dependencies:

  ...
  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>org.jboss.resteasy</groupId>
        <artifactId>resteasy-bom</artifactId>
        <version>4.4.1.Final</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>
  ...
  <dependency>
    <groupId>org.jboss.resteasy</groupId>
    <artifactId>resteasy-client</artifactId>
    <version>4.4.1.Final</version>
    <exclusions>
      <exclusion>
        <groupId>org.jboss.spec.javax.xml.bind</groupId>
        <artifactId>jboss-jaxb-api_2.3_spec</artifactId>
      </exclusion>
      <exclusion>
        <groupId>com.sun.activation</groupId>
        <artifactId>jakarta.activation</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
  <dependency>
    <groupId>org.jboss.resteasy</groupId>
    <artifactId>resteasy-jaxb-provider</artifactId>
    <exclusions>
      <exclusion>
        <groupId>org.jboss.spec.javax.xml.bind</groupId>
        <artifactId>jboss-jaxb-api_2.3_spec</artifactId>
      </exclusion>
      <exclusion>
        <groupId>com.sun.activation</groupId>
        <artifactId>jakarta.activation</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
  <dependency>
    <groupId>org.jboss.resteasy</groupId>
    <artifactId>resteasy-jackson2-provider</artifactId>
  </dependency>
  ...

Please notice the exclusions meant to workaround the maven-shade-plugin which will overload different versions of the same artifacts.

maven-shade-plugin configuration:

...
<plugin>
  <artifactId>maven-shade-plugin</artifactId>
  <version>3.2.1</version>
  <executions>
    <execution>
      <phase>package</phase>
      <goals>
        <goal>shade</goal>
      </goals>
    </execution>
  </executions>
  <configuration>
    <finalName>...</finalName>
    <createDependencyReducedPom>false</createDependencyReducedPom>
      <!-- Using filtering in order to get rid of nasty warnings generated by shading module-info-->
      <filters>
        <filter>
          <artifact>*:*</artifact>
          <excludes>
            <exclude>module-info.class</exclude>
          </excludes>
        </filter>
      </filters>
      <!-- Required as per https://stackoverflow.com/questions/24023155-->
      <transformers>
        <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer" />
        </transformers>
      </configuration>
    </plugin>
    ...

Java client code:

...
private static ResteasyClient client =  new ResteasyClientBuilderImpl().httpEngine(new URLConnectionEngine()).build();
private static WebTarget webTarget = client.target("https://...");
...
webTarget.request().post(Entity.entity(..., "application/json"));
...

Please notice that using JAX-RS pure client as below:

...
private static Client client = ClientBuilder.newClient();
...

won't work and will raise the following exception:

javax.net.ssl.SSLHandshakeException: javax.net.ssl.SSLProtocolException: SSL handshake aborted: ssl=0x7933f1c0: Failure in SSL library, usually a protocol error

Hence, in order to work around this, I needed to use RESTeasy (non JAX-RS) specific stuff, which isn't good. This is a RESTeasy bug and is supposed to have been solved in 4.5. However, due to some deprecations and refactorings (class ResteasyClientBuilderImpl doesn't exist any more, etc.) I preferred stay with the 4.4.

So, doing like this works as expected, the Lambda functions successfully call the REST endpoints exposed through API Gateway and I don't need to use the huge Java library generated with AWS console.