Question

为什么由java.lang.NoClassDefFoundError引起的client JAR崩溃ClassNotFoundException，但是来自gradle的run工作正常？客户端如何使用library JAR？

存在问题

thufir@mordor:~/NetBeansProjects/hello_client$ 
thufir@mordor:~/NetBeansProjects/hello_client$ gradle clean build
Starting a new Gradle Daemon for this build (subsequent builds will be faster).
Download https://jitpack.io/com/github/THUFIR/hello_api/dev/hello_api-dev.pom
Download https://repo1.maven.org/maven2/org/codehaus/groovy/groovy-all/2.4.1/groovy-all-2.4.1.pom
Download https://jitpack.io/com/github/THUFIR/hello_api/dev/hello_api-dev.jar
Download https://repo1.maven.org/maven2/org/codehaus/groovy/groovy-all/2.4.1/groovy-all-2.4.1.jar
Changed strategy of configuration ':compile' after it has been resolved. This behaviour has been deprecated and is scheduled to be removed in Gradle 3.0
:clean
:compileJava
:processResources UP-TO-DATE
:classes
:jar
:startScripts
:distTar
:distZip
:assemble
:compileTestJava UP-TO-DATE
:processTestResources UP-TO-DATE
:testClasses UP-TO-DATE
:test UP-TO-DATE
:check UP-TO-DATE
:build

BUILD SUCCESSFUL

Total time: 1 mins 11.959 secs
thufir@mordor:~/NetBeansProjects/hello_client$ 
thufir@mordor:~/NetBeansProjects/hello_client$ java -jar build/libs/hello_client.jar 
Exception in thread "main" java.lang.NoClassDefFoundError: net/bounceme/mordor/hello/library/HelloLibrary
    at net.bounceme.mordor.hello.client.Client.runLibrary(Client.java:13)
    at net.bounceme.mordor.hello.client.Client.main(Client.java:9)
Caused by: java.lang.ClassNotFoundException: net.bounceme.mordor.hello.library.HelloLibrary
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 2 more
thufir@mordor:~/NetBeansProjects/hello_client$ 
thufir@mordor:~/NetBeansProjects/hello_client$ gradle clean run
Changed strategy of configuration ':compile' after it has been resolved. This behaviour has been deprecated and is scheduled to be removed in Gradle 3.0
:clean
:compileJava
:processResources UP-TO-DATE
:classes
:run
hello [fred]

BUILD SUCCESSFUL

Total time: 4.66 secs
thufir@mordor:~/NetBeansProjects/hello_client$

应该如此，上面的输出是“你好[fred]”，这很好。 hello world客户端代码：

package net.bounceme.mordor.hello.client;

import static java.lang.System.out;
import net.bounceme.mordor.hello.library.HelloLibrary;

public class Client {

    public static void main(String[] args) {
        new Client().runLibrary();
    }

    private void runLibrary() {
        HelloLibrary library = new HelloLibrary();
        out.println(library.hello("fred"));
    }

}

Netbeans抱怨net.bounceme.mordor.hello.library.HelloLibrary的导入声明，这似乎是正确的：

thufir@mordor:~$ 
thufir@mordor:~$ cp .gradle/caches/modules-2/files-2.1/com.github.THUFIR/hello_api/dev/fa670823cfe9548b87c75f224a48a1089eab0b35/hello_api-dev.jar jar
thufir@mordor:~$ 
thufir@mordor:~$ cd jar
thufir@mordor:~/jar$ 
thufir@mordor:~/jar$ jar -xf hello_api-dev.jar 
thufir@mordor:~/jar$ 
thufir@mordor:~/jar$ cat META-INF/MANIFEST.MF 
Manifest-Version: 1.0

thufir@mordor:~/jar$           
thufir@mordor:~/jar$ ll net/bounceme/mordor/hello/library/HelloLibrary.class 
-rw-rw-r-- 1 thufir thufir 728 Mar 11  2016 net/bounceme/mordor/hello/library/HelloLibrary.class
thufir@mordor:~/jar$

这是客户端JAR：

thufir@mordor:~/NetBeansProjects/hello_client$              
thufir@mordor:~/NetBeansProjects/hello_client$ cd build/libs/
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ jar -xf hello_client.jar 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ cat META-INF/MANIFEST.MF 
Manifest-Version: 1.0
Main-Class: net.bounceme.mordor.hello.client.Client
Class-Path: hello_api-dev.jar groovy-all-2.4.1.jar

thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ ll net/bounceme/mordor/hello/client/Client.class 
-rw-rw-r-- 1 thufir thufir 912 Mar 11 02:28 net/bounceme/mordor/hello/client/Client.class
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$

对我来说，似乎类路径正确包含hello_api-dev.jar。

这似乎值得注意：

尽可能避免以编译方式使用依赖项 fileTree（dir：'lib'，include：['* .jar']）。基于托管依赖项在诸如Maven或JCenter之类的存储库上更容易使用始终比随机目录中的依赖项。如果是这样的话您不想发布到开源的内部库工件库，那么可能值得设置本地Nexus 实例或类似的。

https://stackoverflow.com/a/35304025/262852

然而，我不太确定这是否是问题所在，因为我似乎正在使用正确的JAR，使用正确的包装，来自jitpack。

我甚至将libary添加到客户端的libs文件夹中：

thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ jar -vft hello_client.jar 
     0 Fri Mar 11 02:50:28 PST 2016 META-INF/
   135 Fri Mar 11 02:50:28 PST 2016 META-INF/MANIFEST.MF
     0 Fri Mar 11 02:50:28 PST 2016 net/
     0 Fri Mar 11 02:50:28 PST 2016 net/bounceme/
     0 Fri Mar 11 02:50:28 PST 2016 net/bounceme/mordor/
     0 Fri Mar 11 02:50:28 PST 2016 net/bounceme/mordor/hello/
     0 Fri Mar 11 02:50:28 PST 2016 net/bounceme/mordor/hello/client/
   927 Fri Mar 11 02:50:28 PST 2016 net/bounceme/mordor/hello/client/HelloClient.class
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ jar -vft libs/hello_api-dev.jar 
     0 Fri Mar 11 01:59:38 PST 2016 META-INF/
    25 Fri Mar 11 01:59:38 PST 2016 META-INF/MANIFEST.MF
     0 Fri Mar 11 01:59:38 PST 2016 net/
     0 Fri Mar 11 01:59:38 PST 2016 net/bounceme/
     0 Fri Mar 11 01:59:38 PST 2016 net/bounceme/mordor/
     0 Fri Mar 11 01:59:38 PST 2016 net/bounceme/mordor/hello/
     0 Fri Mar 11 01:59:38 PST 2016 net/bounceme/mordor/hello/library/
   728 Fri Mar 11 01:59:38 PST 2016 net/bounceme/mordor/hello/library/HelloLibrary.class
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ java -jar hello_client.jar 
Exception in thread "main" java.lang.NoClassDefFoundError: net/bounceme/mordor/hello/library/HelloLibrary
    at net.bounceme.mordor.hello.client.HelloClient.runLibrary(HelloClient.java:13)
    at net.bounceme.mordor.hello.client.HelloClient.main(HelloClient.java:9)
Caused by: java.lang.ClassNotFoundException: net.bounceme.mordor.hello.library.HelloLibrary
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 2 more
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$

这引出了一个问题：为什么不为客户端重复复制库？

Answer 1

组装机：

thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ cp /home/thufir/.gradle/caches/modules-2/files-2.1/org.codehaus.groovy/groovy-all/2.4.1/a9ca9c9de09361ec2a18d2c058d2524fbd8eae0c/groovy-all-2.4.1.jar hello_api-dev.jar hello_client.jar .
cp: ‘hello_api-dev.jar’ and ‘./hello_api-dev.jar’ are the same file
cp: ‘hello_client.jar’ and ‘./hello_client.jar’ are the same file
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ jar -i hello_client.jar 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ ll
total 6816
drwxrwxr-x 2 thufir thufir    4096 Mar 11 03:41 ./
drwxrwxr-x 6 thufir thufir    4096 Mar 11 03:30 ../
-rw-rw-r-- 1 thufir thufir 6937913 Mar 11 03:41 groovy-all-2.4.1.jar
-rw-rw-r-- 1 thufir thufir    1422 Mar 11 03:39 hello_api-dev.jar
-rw-rw-r-- 1 thufir thufir    2722 Mar 11 03:41 hello_client.jar
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ 
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$ java -jar hello_client.jar 
hello [fred]
thufir@mordor:~/NetBeansProjects/hello_client/build/libs$

1.。）为什么这样做？

2。）构建这些JAR的正确方法是什么？

这必须是少数（如果不仅仅是）阅读精细手册实际上有用的情况之一。我看到了“i”开关，它显示：

thufir@mordor:~/NetBeansProjects/hello_client$ 
thufir@mordor:~/NetBeansProjects/hello_client$ jar -i build/libs/hello_client.jar 
java.io.FileNotFoundException: build/libs/hello_api-dev.jar (No such file or directory)
    at java.util.zip.ZipFile.open(Native Method)
    at java.util.zip.ZipFile.<init>(ZipFile.java:219)
    at java.util.zip.ZipFile.<init>(ZipFile.java:149)
    at java.util.jar.JarFile.<init>(JarFile.java:166)
    at java.util.jar.JarFile.<init>(JarFile.java:103)
    at sun.tools.jar.Main.getJarPath(Main.java:1163)
    at sun.tools.jar.Main.getJarPath(Main.java:1179)
    at sun.tools.jar.Main.genIndex(Main.java:1195)
    at sun.tools.jar.Main.run(Main.java:317)
    at sun.tools.jar.Main.main(Main.java:1288)
thufir@mordor:~/NetBeansProjects/hello_client$

但是，我真的不明白那个输出，只是觉得很奇怪它是一个“找不到文件”的例外。

gradle run执行;使用ClassNotFoundException

1 个答案: