How to get access to javax.annotation.Resource at run time in Java 9

问题

I have a test:

public class ResourceTest {
    @Test
    public void test() throws ClassNotFoundException {
        Class.forName("javax.annotation.Resource");
    }
}

It tries to access javax.annotation.Resource. In java 8 it worked, but in java 9 (I'm using Oracle JDK 9) it fails with ClassNotFoundException. As explained here Spring: @Resource injection stopped working under JDK9 , javax.annotation.Resource from the JDK is not available by default in Java 9.

I'm trying to get access to it using module descriptor:

module test {
    requires java.xml.ws.annotation;
    requires junit;
}

Here, I specifically request access to java.xml.ws.annotation module (which contains javax.annotation.Resource). But the test still fails.

When I remove that requires clause and add a dependency (as a library) which contains javax.annotations.Resource, it works:

    <dependency>
        <groupId>javax.annotation</groupId>
        <artifactId>javax.annotation-api</artifactId>
        <version>1.3.1</version>
    </dependency>

When I add them both (Maven dependency in pom.xml and requires java.xml.ws.annotation), compilation in IDEA fails with the following message:

the unnamed module reads package javax.annotation from both java.xml.ws.annotation and java.annotation

But Maven build still succeeds!

If I add java.xml.ws.annotation module via command line, it works (with no Maven dependency and with requires clause):

mvn clean test -DargLine="--add-modules java.xml.ws.annotation"

Do I do something wrong with my module description? How can I get access to JDK-supplied javax.annotation.Resource without command line switches?

The test project is available at https://github.com/rpuch/test-resource-jdk9

回答1:

Just to clear out some confusion here. The ways to work stated in the question by you are alternatives and should not be combined as you have already seen.

the unnamed module reads package javax.annotation from both java.xml.ws.annotation and java.annotation

So the way it would work is either:

You can use the compiler args to add modules

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.7.0</version>
    <configuration>
        <release>9</release>
        <compilerArgs>
            <arg>--add-modules</arg>
            <arg>java.xml.ws.annotation</arg>
        </compilerArgs>
    </configuration>
</plugin>

OR

Make use of the javax.xml.ws.annotation being an upgradeable module which is when you can make use of the dependency

<dependency>
    <groupId>javax.annotation</groupId>
    <artifactId>javax.annotation-api</artifactId>
    <version>1.3.1</version>
</dependency>

Ideally this would be a preferrable option to stick to as the former is just an alternate to use the @Deprecated module marked forRemoval.

So the required clause by itself it not enough to get access to a module... is this true for all JDK-supplied modules (excluding java.base), or it is only true for deprecated modules?

No, the requires is just a part of declaration. [Think about this, prior to JDK 9 if you used a statement import some.foo.bar; in your class which was not added as a library(classpath) would that have worked?]. The module marked as required has to be on the modulepath for you to access it.

Update - The first option would not be supported any time longer with the use of JDK/11 or above wherein the JEP to Remove the Java EE and CORBA Modules is targetted.

回答2:

For gradle build, adding the following to build.gradle works:

compile 'javax.annotation:jsr250-api:1.0'

tasks.withType(AbstractCompile) {
    options.compilerArgs += ["--add-modules", "java.xml.bind"]
}

tasks.withType(Test) {
    jvmArgs += ["--add-modules", "java.xml.bind"]
}

来源：https://stackoverflow.com/questions/46502001/how-to-get-access-to-javax-annotation-resource-at-run-time-in-java-9

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java

java-9

java-module