Implementing UPDATE operation

Previously, we created and read blog posts. Now, let's implement and make a call to update a blog post. We'll also learn how to handle an exception with a custom exception handler.

What you need

You need to have the following files obtained from previous steps. You can always download the full version, instead of creating one yourself.

1. Implement server-side

Let's implement the server-side for updating blog posts. This time, we'll use a custom exception handler.

Add an exception handler

First, add a custom exception handler for the blog service.

  1. Create a class for the exception to be thrown when a specified blog post ID doesn't exist.

    BlogNotFoundException.java
    package example.armeria.server.blog.grpc;

final class BlogNotFoundException extends IllegalStateException {
  BlogNotFoundException(String s) {
      super(s);
  }
}

  2. Add an exception handler class for the blog service.

    GrpcExceptionHandler.java
    package example.armeria.server.blog.grpc;

import com.linecorp.armeria.common.RequestContext;
import com.linecorp.armeria.common.annotation.Nullable;
import com.linecorp.armeria.common.grpc.GrpcExceptionHandlerFunction;

import io.grpc.Metadata;
import io.grpc.Status;

public class GrpcExceptionHandler implements GrpcExceptionHandlerFunction {

  @Nullable
  @Override
  public Status apply(RequestContext ctx, Throwable cause, Metadata metadata) {
    if (cause instanceof IllegalArgumentException) {
        return Status.INVALID_ARGUMENT.withCause(cause);
    }
    if (cause instanceof BlogNotFoundException) {
        return Status.NOT_FOUND.withCause(cause).withDescription(cause.getMessage());
    }

    // The default mapping function will be applied.
    return null;
  }
}

  3. In the Main class, bind the GrpcExceptionHandler to our service.

    Main.java
    private static Server newServer(int port) throws Exception {
  final GrpcService grpcService =
     GrpcService.builder()
                .addService(new BlogService())
                .exceptionMapping(new GrpcExceptionHandler()) // Add this
                .build();
  ...
}

Implement the service method

In the BlogServiceImpl class, add a service method for updating a blog post.

BlogService.java
import example.armeria.blog.grpc.UpdateBlogPostRequest;

public class BlogService extends BlogServiceGrpc.BlogServiceImplBase {
  @Override
  public void updateBlogPost(UpdateBlogPostRequest request, StreamObserver<BlogPost> responseObserver) {
    final BlogPost oldBlogPost = blogPosts.get(request.getId());
    if (oldBlogPost == null) {
      throw new BlogNotFoundException("The blog post does not exist. ID: " + request.getId());
    } else {
      final BlogPost newBlogPost = oldBlogPost.toBuilder()
                .setTitle(request.getTitle())
                .setContent(request.getContent())
                .setModifiedAt(Instant.now().toEpochMilli())
                .build();
      blogPosts.put(request.getId(), newBlogPost);
      responseObserver.onNext(newBlogPost);
      responseObserver.onCompleted();
    }
  }
}

3. Test updating a blog post

Let's try updating the content of the first blog post. Add a method like the following.

BlogServiceTest.java
@Test
@Order(5)
void updateBlogPosts() throws JsonProcessingException {
  final UpdateBlogPostRequest request = UpdateBlogPostRequest.newBuilder()
              .setId(0)
              .setTitle("My first blog")
              .setContent("Hello awesome Armeria!")
              .build();
  final BlogPost updated = client.updateBlogPost(request);
  assertThat(updated.getId()).isZero();
  assertThat(updated.getTitle()).isEqualTo("My first blog");
  assertThat(updated.getContent()).isEqualTo("Hello awesome Armeria!");
}

Run all the test cases on your IDE or using Gradle. Check that you see the test is passed.

4. Test an error case

To check that our exception handler is working, let's try updating a post which does not exist.

  1. Bind the exception handler to the service for the test server.
    BlogServiceTest.java
    @RegisterExtension
static final ServerExtension server = new ServerExtension() {
  @Override
  protected void configure(ServerBuilder sb) throws Exception {
    sb.service(GrpcService.builder()
              .addService(new BlogService())
              .exceptionHandler(new GrpcExceptionHandler()) // Add this
              .build());
  }
};
  2. Add a test method to update a blog post with an invalid ID, asserting an exception is thrown as expected.
    BlogServiceTest.java
    @Test
@Order(6)
void updateInvalidBlogPost() {
  final Throwable exception = catchThrowable(() -> {
     client.updateBlogPost(UpdateBlogPostRequest.newBuilder()
              .setId(Integer.MAX_VALUE)
              .setTitle("My first blog")
              .setContent("Hello awesome Armeria!")
              .build());
  });
  final StatusRuntimeException statusException = (StatusRuntimeException) exception;
  assertThat(statusException.getStatus().getCode()).isEqualTo(Code.NOT_FOUND);
  assertThat(statusException)
              .hasMessageContaining("The blog post does not exist. ID: " + Integer.MAX_VALUE);
}
  3. Run all the test cases on your IDE or using Gradle. Check that you see the test is passed.

What's next

In this step, we've implemented a service method for updating a blog post. We've also added an exception handler.

Next, at Step 6. Implement DELETE, we'll implement a method for deleting a blog post and add a Documentation Service to our service.

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