Debugging a REST service with VSCode

If you are looking to debug a REST service with VSCode then follow along!

In 6 steps you will learn how to start debugging the REST service. They are:

Create the Maven POM file
Add the application class
Add the endpoint
Add the VSCode tasks.json file
Add the VSCode launch.json file
Debug the application

Create the Maven POM file

Create an empty directory to store your Maven project. Inside of that directory create the pom.xml file with the content as below.

<?xml version="1.0" encoding="UTF-8"?>

<project
    xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>cloud.piranha.guides.coreprofile</groupId>
    <artifactId>vscode-debug</artifactId>
    <version>1-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>Piranha Core Profile - Debugging a REST service with VSCode</name>
    <properties>
        <jakartaee.version>10.0.0</jakartaee.version>
        <java.version>17</java.version>
        <junit.version>5.10.0-M1</junit.version>
        <maven-compiler-plugin.version>3.11.0</maven-compiler-plugin.version>
        <maven-failsafe-plugin.version>3.0.0</maven-failsafe-plugin.version>
        <maven-war-plugin.version>3.3.2</maven-war-plugin.version>
        <piranha.version>23.6.0</piranha.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <dependency>
            <groupId>jakarta.platform</groupId>
            <artifactId>jakarta.jakartaee-core-api</artifactId>
            <version>${jakartaee.version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-params</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <finalName>rest</finalName>
        <plugins>
            <plugin>
                <groupId>cloud.piranha.maven.plugins</groupId>
                <artifactId>piranha-maven-plugin</artifactId>
                <version>${piranha.version}</version>
                <executions>
                    <execution>
                        <id>pre-integration-test</id>
                        <phase>pre-integration-test</phase>
                        <goals>
                            <goal>start</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>post-integration-test</id>
                        <phase>post-integration-test</phase>
                        <goals>
                            <goal>stop</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${maven-compiler-plugin.version}</version>
                <configuration>
                    <release>${java.version}</release>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-failsafe-plugin</artifactId>
                <version>${maven-failsafe-plugin.version}</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>integration-test</goal>
                            <goal>verify</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>${maven-war-plugin.version}</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <profiles>
        <profile>
            <id>debug</id>
            <build>
                <plugins>
                    <plugin>
                        <groupId>cloud.piranha.maven.plugins</groupId>
                        <artifactId>piranha-maven-plugin</artifactId>
                        <version>${piranha.version}</version>
                        <configuration>
                            <jvmArguments>-Xdebug -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=9009</jvmArguments>
                        </configuration>
                    </plugin>
                </plugins>
            </build>
        </profile>
    </profiles>
</project>

Note the POM file contains a debug profile in the profiles section that we will leverage later on to activate the VSCode debugging.

Add the application class

Add the Application class in the src/main/java directory, which allows you to set the application path using the @ApplicationPath annotation.

package rest;

import jakarta.ws.rs.ApplicationPath;
import jakarta.ws.rs.core.Application;

@ApplicationPath("")
public class RestApplication extends Application {
}

Add the endpoint

And we are adding a simple ‘Hello World’ endpoint that is listening on the /helloworld path.

package rest;

import jakarta.enterprise.context.RequestScoped;
import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;

@Path("/helloworld")
@RequestScoped
public class HelloWorldBean {

    @GET
    public String helloWorld() {
        return "Hello World!";
    }
}

Add the VSCode tasks.json file

To integrate debugging into VSCode we’ll need a tasks.json file that will trigger the proper Maven goals BEFORE we start the debugger. For that lets first create the .vscode directory in the root directory of your Maven project (if it does not exist). And then we will create the tasks.json file in the .vscode directory. It should contain the content as below.

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "Start",
            "type": "shell",
            "command": "mvn -Pdebug package pre-integration-test",
            "isBackground": true,
            "problemMatcher": "$tsc-watch",
        }
    ]
}

Add the VSCode launch.json file

The next step is to configure the launch.json file to allow it to attach to the REST service after it gets started by means of the Start entry in the tasks.json file.

For that we will create the tasks.json file in the .vscode directory with the content as below.

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "java",
            "name": "Debug",
            "preLaunchTask": "Start",
            "request": "attach",
            "hostName": "localhost",
            "port": "9009"
        }
    ]
}

Debug the application

Open the HelloWorldBean.java file and set a breakpoint on the line where the Hello World response is returned.

Then on your left bar click on the Debug icon.

And make sure that Debug is selected and click the run icon to the left of it.

Then browse to http://localhost:8080/rest/helloworld/.

Now you’ll see it hit your breakpoint.

Conclusion

Setting up debugging for VSCode requires a little bit of plumbing, but once the Maven profile, the VSCode tasks.json and launch.json files are in place it all comes together nicely!

References

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