jar 中的类可以使用不同 jar 中的类吗

Question

我是 java 新手，所以不确定我是否完全理解 jar 文件。

我想将一些通用代码放入库 jar 中，然后我可以从不同 jar 中的应用程序中使用这些代码。我已经对此进行了搜索，但只有人说是，然后显示类文件中的类调用 jar 中的类的示例，这与 jar 中的类调用不同 jar 中的类不同。

我已经尝试过这样做，并认为我可以正常工作，直到我尝试在命令行上运行应用程序，此时我得到类未找到错误。然而，代码在 eclipse 中运行，从我所见，这似乎是一个常见问题，即代码在正在开发的 ide 中运行，但是当有人试图在 eclipse 之外运行他们的代码时，它就会失败。

那么构建为 jar 的应用程序是否可以调用/使用不同 jar 文件中的类？如果可以，如何实现？

这是我试图测试的问题

FoobarInterface.java

package org.myorg.mylibrary;

public interface FoobarInterface
{
    String echo(final String val);
}

Foobar.java

package org.myorg.mylibrary;

public class Foobar implements FoobarInterface
{

    public String echo(final String val)
    {
        StringBuilder sb = new StringBuilder("echoed: ");
        sb.append(val);
        return(sb.toString());
    }

}

库 jar 的 pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.myorg</groupId>
  <artifactId>mylibrary</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>mylibraryname</name>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <configuration>
          <archive>
            <index>true</index>
            <manifest>
            </manifest>
          </archive>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

产生 mylibrary-0.0.1-SNAPSHOT.jar

客户端代码是

Main.java

package org.myorg.myapp;

import org.myorg.mylibrary.Foobar;

public class Main
{

    public Main(String[] args)
    {
        Foobar foobar = new Foobar();
        StringBuilder sb = new StringBuilder("RESULT: ");
        sb.append(foobar.echo(args[0]));
        System.out.println(sb.toString());
    }

    public static void main(String[] args)
    {
        Main foo = new Main(args);
    }

}

应用 jar 的 pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
      <modelVersion>4.0.0</modelVersion>
      <groupId>org.myorg</groupId>
      <artifactId>myapp</artifactId>
      <version>0.0.1-SNAPSHOT</version>
      <name>myappname</name>
      <dependencies>
        <dependency>
            <groupId>org.myorg</groupId>
            <artifactId>mylibrary</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>
      </dependencies>

      <build>
        <plugins>
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-jar-plugin</artifactId>
            <configuration>
              <archive>
                <index>true</index>
                <manifest>
                  <mainClass>org.myorg.myapp.Main</mainClass>
                </manifest>
                <manifestEntries>
                 <Class-Path>.</Class-Path>
                </manifestEntries>
              </archive>
            </configuration>
          </plugin>
        </plugins>
      </build>
    </project>

我也尝试了 Class-Path 元素的所有这些设置

. ./mylibrary-0.0.1-SNAPSHOT.jar mylibrary-0.0.1-SNAPSHOT.jar

所以理论上我可以使用这个命令运行应用程序

java -jar myapp-0.0.1-SNAPSHOT.jar

但我总是收到此错误

Exception in thread "main" java.lang.NoClassDefFoundError: org/myorg/mylibrary/Foobar

无论我如何在应用程序 pom.xml 中指定 Class-Path 元素，也无论我是否将类路径添加到命令行，例如

java -classpath mylibrary-0.0.1-SNAPSHOT.jar -jar myapp-0.0.1-SNAPSHOT.jar

是的，两个 jar 都在同一个目录中，我在 linux 上运行它。

编辑：

JB Nizet 要求以 java -jar 的身份运行命令的结果，但不幸的是，我已经删除了测试代码，因为他让我解决了问题。但是，如果有任何好处，这里是第一次为我提出问题的源的输出，仍然显示相同的异常，但现在也正在使用他建议的第二个命令。

java -jar FoobarGUI-0.0.1-SNAPSHOT.jar org.myorg.foobar.gui.Main
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
        at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1770)
        at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1653)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
        at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
        at javafx.event.Event.fireEvent(Event.java:198)
        at javafx.scene.Node.fireEvent(Node.java:8390)
        at javafx.scene.control.Button.fire(Button.java:185)
        at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
        at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
        at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
        at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)                                        
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)                                             
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)                                        
        at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)                                                                   
        at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)                                                                       
        at javafx.event.Event.fireEvent(Event.java:198)                                                                                      
        at javafx.scene.Scene$MouseHandler.process(Scene.java:3758)                                                                          
        at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3486)                                                                      
        at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)                                                                        
        at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2495)                                                                  
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:350)                        
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)                        
        at java.security.AccessController.doPrivileged(Native Method)                                                                        
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$350(GlassViewEventHandler.java:385)                       
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$$Lambda$201/45156577.get(Unknown Source)                                          
        at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:404)                                            
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:384)                                  
        at com.sun.glass.ui.View.handleMouseEvent(View.java:555)                                                                             
        at com.sun.glass.ui.View.notifyMouse(View.java:927)                                                                                  
        at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)                                                                       
        at com.sun.glass.ui.gtk.GtkApplication.lambda$null$48(GtkApplication.java:139)                                                       
        at com.sun.glass.ui.gtk.GtkApplication$$Lambda$41/1364335809.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
        at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
        at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1767)
        ... 50 more
Caused by: java.lang.NoClassDefFoundError: org/myorg/foobar/processor/ProcessorException
        at org.myorg.foobar.gui.Main.initCenterSection(Main.java:244)
        at org.myorg.foobar.gui.Main.initApplicationScene(Main.java:195)
        at org.myorg.foobar.gui.Main.actionLogin(Main.java:413)
        at org.myorg.foobar.gui.controller.ControllerLogin.actionLogin(ControllerLogin.java:97)
        ... 60 more
Caused by: java.lang.ClassNotFoundException: org.myorg.foobar.processor.ProcessorException
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        ... 64 more

已分解的应用程序 jar 中的 META-INF/MANIFEST.MF

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Built-By: myorg
Class-Path: FoobarProcessor-0.0.1-SNAPSHOT.jar
Created-By: Apache Maven 3.3.3
Build-Jdk: 1.8.0_45
Main-Class: org.myorg.foobar.gui.Main

这是处理器库 jar 的列表

META-INF/
META-INF/MANIFEST.MF
org/
org/myorg/
org/myorg/foobar/
org/myorg/foobar/processor/
org/myorg/foobar/processor/ProcessorException.class
org/myorg/foobar/processor/Processor.class
META-INF/maven/
META-INF/maven/org.myorg.foobar/
META-INF/maven/org.myorg.foobar/FoobarProcessor/
META-INF/maven/org.myorg.foobar/FoobarProcessor/pom.xml
META-INF/maven/org.myorg.foobar/FoobarProcessor/pom.properties
META-INF/INDEX.LIST

这是来自库 jar 的 META-INF/MANIFEST.MF

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Built-By: myorg
Created-By: Apache Maven 3.3.3
Build-Jdk: 1.8.0_45

Answer 1

如果应用jar文件的manifest的Class-Path属性是

mylibrary-0.0.1-SNAPSHOT.jar

并且两个jar文件在同一个目录下，然后运行

java -jar myapp-0.0.1-SNAPSHOT.jar should work.

你也可以显式设置类路径，显式设置主类，这样更容易，并且不依赖清单中的相对路径。

java -cp myapp-0.0.1-SNAPSHOT.jar:mylibrary-0.0.1-SNAPSHOT.jar org.myorg.myapp.Main

您不应在同一命令中使用 -classpath 和 -jar 选项。这是一个或另一个。

Answer 2

尝试在 pom.xml 中进行一些修改

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <configuration>
        <archive>
            <manifest>
                <mainClass>org.myorg.myapp.Main</mainClass>
                <addClasspath>true</addClasspath>
            </manifest>
        </archive>
    </configuration>
</plugin>

在此之后，如果您仍然有问题，只需使用任何解压缩工具解压缩您的 myapp-0.0.1-SNAPSHOT.jar。解压后查看 META-INF 文件夹下 MANIFEST 文件中 mylibrary-0.0.1-SNAPSHOT.jar 的路径。

Answer 3

This should be marked as a duplicate of this question I just came across

这是确切的问题和解决方案，在我确切知道我在搜索什么之前，我无法通过之前的所有搜索找到它，即 Executable JAR 忽略其自己的 Class-Path 属性

所以根本不是 java 问题，而是 maven 问题，而且通常稀疏的 maven 文档根本没有说明问题。不幸的是，我复制的示例配置包含该设置，默认情况下该设置已关闭。最终解决方案，不要在 maven 插件中使用索引。