JPMS ServiceLoader 对我不起作用

Question

JPMS ServiceLoader 无法正常工作。

我正在尝试提供一个 桌面程序作为可执行 jar 具有默认服务，可以由个人用户超载。用户提供他们自己的服务 class 并在命令行上将他们的名字作为参数提供。

服务:

package eu.ngong.myService;

public interface MyService {
    public String name();
    public void doSomething();
}

程序连同默认服务（if和if中的第一行for 被插入用于日志记录):

package eu.ngong.myService;

import java.util.ServiceLoader;

public class ServiceUser implements MyService {
    private static MyService myService = new ServiceUser();

    public static void main(String[] args) {
        if (args.length > 0) {
            System.out.println("trying to load " + args[0] + " envirionment.");
            ServiceLoader<MyService> myServices = ServiceLoader.load(MyService.class);
            for (MyService ms : myServices) {
                System.out.println(ms.name());
                if (ms.name().equalsIgnoreCase(args[0])) {
                    myService = ms;
                }
            }
        }
        myService.doSomething();
    }

    @Override
    public void doSomething() {
        System.out.println("The default service is acting.");
    }

    @Override
    public String name() {
        return "Default";
    }
}

两者都收集在 myService.jar 中，主要 class ServiceUser 托管模块-info.java

module MyService {
    exports eu.ngong.myService;
    provides eu.ngong.myService.MyService with eu.ngong.myService.ServiceUser;
}

用户的个人jar可能

package eu.ngong.user1;
import eu.ngong.myService.MyService;
public class User1 implements MyService {

    @Override
    public String name() {
        return "User1";
    }

    @Override
    public void doSomething() {
        System.out.println("User1 is acting.");
    }

}

与模块-info.java

module User1 {
    requires MyService;
    provides eu.ngong.myService.MyService with eu.ngong.user1.User1;
}

但是，运行程序与

java -p ..\user1\user1.jar;myService.jar -jar myService.jar User1

仅导致意外输出

trying to load User1 environment.
The default service is acting.

虽然我预期有日志记录

trying to load User1 environment.
Default
User1
User1 is acting.

我错过了什么？

Answer 1

您需要申报
```
uses eu.ngong.myService.MyService;
```

在您要执行服务加载代码的模块中。

尝试确保您的包装已添加 META-INF/services，以便在自动处理时通过 jar 文件正确解析模块。

由于这不适合评论，因此在此分享类似示例的发现。在通过 IntelliJ 执行时，我可以注意到该代码仅适用于 uses 声明和 user-service 模块的类路径。

此外，我尝试使用类似的命令行：

java --show-module-resolution -p base-service/target/classes:user-service/target/classes --add-modules base.service,user.service -m base.service/base.service.ServiceUser user1
root base.service file://.../base-service/target/classes/
root user.service file://.../user-service/target/classes/
user.service requires base.service file://.../base-service/target/classes/
base.service binds user.service file://.../user-service/target/classes/
...
trying to load user1 environment.
Services found : 2
User1
Default
User1 is acting.

并添加了 to seek why providing the jar's on the module path didn't work. The output was as follows and had a difference where the service module was 用户模块。

java --show-module-resolution -p base-service/target/base-service-1.0-SNAPSHOT.jar:user-service/target/user-service-1.0-SNAPSHOT.jar --add-modules base.service,user.service -m base.service/base.service.ServiceUser user1
root base.service file://...base-service/target/base-service-1.0-SNAPSHOT.jar automatic
root user.service file://...user-service/target/user-service-1.0-SNAPSHOT.jar
user.service requires base.service file://...base-service/target/base-service-1.0-SNAPSHOT.jar automatic
.....
trying to load user1 environment.
Services found : 1
User1
User1 is acting.

这也可能是您执行方式出现意外输出的原因。对我来说，Default 实现的细微差别在后者中没有得到解决。

JPMS ServiceLoader 对我不起作用

JPMS ServiceLoader does not work for me as expected

java

java-platform-module-system

serviceloader