Java 9-无法解析为模块

Question

Very simple use case, I am using Eclipse Oxygen 4.7.3a which includes support from Java 9. I have two projects that are Java 9 projects:

- projectOne
| - src
| - module-info.java
  | - com
    | - package1
      | - first
        | Classificator.java

- projectTwo
| - src
| - module-info.java
  | - com
    | - package2
      | - second
        | Classifiable.java

I want to use the Classifiable class inside the Classificator , so I try to import the second module into the first project.

module-info.java Project 1:

module projectOne   {
    requires projectTwo;
}

module-info.java Project 2:

module projectTwo   {

}

Eclipse is giving me the error:

projectTwo cannot be resolved to a module

Do I have to gather all my Java projects under one "main project" in order to let Eclipse know that all those modules are usable inside it ? Or something else I missed ?

Answer 1

No, you don't need them to be in the same directory. Ideally, your project-one module defines some uses , which are implements by your project-two module (or vice-versa). Get the runtime implementation of your used interfaces. For this, both jars/classes must be on the module path.

For further information on module build, multi module builds,... you can refer to this link . Even if you do not use gradle, its tutorial on java 9 module build is quite interesting and gives some insight.

Answer 2

While wiring as a service is certainly a viable approach (as described in the other answer), let me add that requires can be made to work, too, of course.

The thing that was probably missing from the first approach is: Eclipse still needs to know where to look for modules. In real world projects this will typically be mediated by your build tool of choice plus a plug-in like m2e or buildship .

If no such plug-in is used, a normal project dependency should be added to the Build Path of project projectOne in order to make project projectTwo visible. Once the project is on the Build Path the module defined by the project can be resolved in references in module-info.java .