Unable to get resources when using modules in Gradle and IntelliJ

environment

Java

openjdk 11 2018-09-25

Gradle

Gradle 4.10.2

IntelliJ

IntelliJ IDEA 2018.2.4 (Community Edition)
Build #IC-182.4505.22, built on September 18, 2018

OS

Windows 10

Problems that occur

Project structure

|-build.gradle
`-src/main/
  |-java/
  | |-module-info.java
  | `-foo/
  |   `-Foo.java
  `-resources/
    `-resource.txt

code

build.gradle

apply plugin: "application"

sourceCompatibility = 11
targetCompatibility = 11

compileJava.options.encoding = "UTF-8"
mainClassName = "foo/foo.Foo"

compileJava {
    doFirst {
        options.compilerArgs = [
            "--module-path", classpath.asPath
        ]
        classpath = files()
    }
}

run {
    doFirst {
        jvmArgs = [
            "--module-path", classpath.asPath,
            "--module", mainClassName
        ]
        classpath = files()
    }
}

module-info.java

module foo {
    exports foo;
}

Foo.java

package foo;

import java.net.URL;

public class Foo {

    public static void main(String[] args) throws Exception {
        URL resource = Foo.class.getResource("/resource.txt");
        System.out.println("resource=" + resource);
    }
}

Execution result

> gradle run
resource=null

-- /resource.txt cannot be obtained and becomes null --Same result when imported into IntelliJ --By the way, you can get it without any problem with Eclipse (Photon).

Cause (probably)

--In Gradle and IntelliJ, the build results of src / main / java and src / main / resources are output to different directories.

gradle build result

|-build
: |-classes/java/main/
: | `-foo/
: |   `-Foo.class
: |
: |-resources/main/
: : `-resource.txt

IntelliJ build results

|-out/production/
: |-classes/
: | `-foo/
: |   `-Foo.class
: |
: `-resources/
:   `-resource.txt

--At this time, check how the module path is set.

Foo.java

package foo;

import java.net.URL;
import java.util.stream.Stream;

public class Foo {

    public static void main(String[] args) throws Exception {
        System.out.println("[jdk.module.path]");
        Stream.of(System.getProperty("jdk.module.path")
                .split(";"))
                .map(p -> "  " + p)
                .forEach(System.out::println);

        URL resource = Foo.class.getResource("/resource.txt");
        System.out.println("resource=" + resource);
    }
}

Gradle execution result

[jdk.module.path]
  ...\build\classes\java\main
  ...\build\resources\main
resource=null

IntelliJ execution result

[jdk.module.path]
  ...\out\production\classes
  ...\out\production\resources
resource=null

--Each is set in the module path --In other words, I feel that the resources directory is treated as a separate module from the foo module. --If you put a directory without module-info.class in the module path, will it be treated as an anonymous module? ?? ?? --In the case of a jar file, the module name is resolved from the file name and it is treated as an automatic module, but in the case of a directory, I do not know what happens. --And when you check the JavaDoc for Class.getResource (String), it explains:

If this class is in a named Module, ** this method will try to find resources in the module **. (Omitted) This method returns null ** if the resource is a non- ".class" resource in a package that is ** not open to the calling module **.

getResource(String) | Class | Java 10

--That is, Class.getResource (String) will only try to find the resources in the module to which the class belongs. --If the resource is another module, the package must be open (ʻopensspecified?) --Ifresourcesis treated as an anonymous module, I feel like I can't access the anonymous module from the named module. --At least the class is inaccessible --I don't know exactly if the resources are also inaccessible --By the way, in the case of Eclipse, bothsrc / main / java and src / main / resourcesare output underbin / main`.

Organize the story

--In case of Gradle, IntelliJ, files under src / main / resources directory are output to directory different from the compilation result under src / main / java. --The output destinations of src / main / java and src / main / resources will be specified in the module path as separate directories. --src / main / resources is treated as a different module than src / main / java (probably an anonymous module?) --Class.getResource (String) seems to basically only be able to access resources in the same module or in an open module --Therefore, files placed under src / main / resources cannot be read as resources.

Expected to the last.

Solution

Can't access resource with Java 10 – IDEs Support (IntelliJ Platform) | JetBrains

It seems that some people are in trouble with the same thing.

The final method explained here is that the output destination of src / main / resources should be the same as the output destination of src / main / java.

build.gradle

apply plugin: "application"
+ apply plugin: 'idea'

sourceCompatibility = 11
targetCompatibility = 11

compileJava.options.encoding = "UTF-8"
mainClassName = "foo/foo.Foo"

+ sourceSets {
+     main {
+         output.resourcesDir = java.outputDir
+     }
+ }
+ 
+ idea.module.outputDir file("out/production/classes")

compileJava {
    doFirst {
        options.compilerArgs = [
            "--module-path", classpath.asPath
        ]
        classpath = files()
    }
}

run {
    doFirst {
        jvmArgs = [
            "--module-path", classpath.asPath,
            "--module", mainClassName
        ]
        classpath = files()
    }
}

--Adjusting the output destination of IntelliJ and the output destination of Gradle respectively

Execution result

Gradle execution result

> gradle run
[jdk.module.path]
  ...\build\classes\java\main
resource=file:/.../build/classes/java/main/resource.txt

IntelliJ execution result

[jdk.module.path]
  ...\out\production\classes
resource=file:/.../out/production/classes/resource.txt

--Resources can now be accessed by aligning the output destinations of src / main / resources.