How to compile Spring Boot applications with Java 8 --parameter flag

Question

Spring documentation tells that, if we compile our project using Java 8 --parameters flag, we can skip giving parameter names in annotations like @PathVariable. That means, we can just use @PathVariable id instead of @PathVariable("id") id.

In a Spring Boot Maven application, I was curious to know how to tell the compiler to use the parameters flag. Is it on by default? Do we need to provide something in the pom.xml?

Answer 1

In Spring Boot 2.0, the --parameters flag should be enabled by default. See yuranos87's answer.

For older versions, in the pom.xml file, you can specify Java compiler options as arguments of the Maven compiler plugin:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <compilerArgs>
            <arg>-parameters</arg>
        </compilerArgs>
    </configuration>
</plugin>

Answer 2

I don't remember needing to do it explicitly in any of my projects. Maybe you just need to add spring-boot-starter-parent(I know, sometimes might not be an option). Otherwise, Spring has already taken care of everything for you.

It is mentioned multiple times in Spring Boot documentation. For example, here:

To allow the input to be mapped to the operation method’s parameters, code implementing an endpoint should be compiled with -parameters. This will happen automatically if you are using Spring Boot’s Gradle plugin or if you are using Maven and spring-boot-starter-parent.

UPDATE

The way Spring Boot does it is quite straight forward(in spring-boot-parent and spring-boot-starter-parent poms):

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>${java.version}</source>
                <target>${java.version}</target>
                <parameters>true</parameters>
            </configuration>
        </plugin>