Java 类路径问题

Question

我已经编译完毕，现在尝试在 ie 目录中使用以下命令从 OSX 和 Fendora 的终端运行 this 程序：

java ie.moguntia.webcrawler.Psucker http://www.wikipedia.org test

但是我收到以下错误：

Exception in thread "main" java.lang.NoClassDefFoundError: ie/moguntia/webcrawler/Psucker
Caused by: java.lang.ClassNotFoundException: ie.moguntia.webcrawler.Psucker
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

我之前没有运行过从命令行使用包的应用程序，因此我无法找出错误。

我尝试使用

export CLASSPATH=.

设置类路径，以便将当前目录添加到类路径中。

目录结构如下：

ie/moguntia/webcrawler/

Answer 1

根据您编译的类所在的位置，您需要在 java 命令中包含该位置，例如如果它们位于

classes

目录中：

java -cp classes ie.moguntia.webcrawler.PSucker http://www.wikipedia.org test

或者如果它们位于当前目录中：

java -cp . ie.moguntia.webcrawler.PSucker http://www.wikipedia.org test

或者只是

java ie.moguntia.webcrawler.PSucker http://www.wikipedia.org test

这是我如何运行它的（解压缩，cd到目录，编译，查找类，运行）：

(13:55:52) ~/Desktop/temp → ll
total 32
-rw-r--r--@ 1 Nils.Winkler  staff    14K 12 Mär 13:41 multiweb.zip

(13:56:01) ~/Desktop/temp → unzip multiweb.zip -d multiweb
Archive:  multiweb.zip
   creating: multiweb/CVS/
   creating: multiweb/ie/
   creating: multiweb/ie/CVS/
   creating: multiweb/ie/moguntia/
   creating: multiweb/ie/moguntia/CVS/
   creating: multiweb/ie/moguntia/threads/
   creating: multiweb/ie/moguntia/threads/CVS/
  inflating: multiweb/ie/moguntia/threads/ControllableThread.java  
  inflating: multiweb/ie/moguntia/threads/MessageReceiver.java  
  inflating: multiweb/ie/moguntia/threads/ObjectQueue.java  
  inflating: multiweb/ie/moguntia/threads/Queue.java  
  inflating: multiweb/ie/moguntia/threads/ThreadController.java  
   creating: multiweb/ie/moguntia/webcrawler/
   creating: multiweb/ie/moguntia/webcrawler/CVS/
  inflating: multiweb/ie/moguntia/webcrawler/PSucker.java  
  inflating: multiweb/ie/moguntia/webcrawler/PSuckerThread.java  
  inflating: multiweb/ie/moguntia/webcrawler/SaveURL.java  
  inflating: multiweb/ie/moguntia/webcrawler/URLQueue.java  
  inflating: multiweb/ie/moguntia/webcrawler/WSDLCrawler.java  
  inflating: multiweb/ie/moguntia/webcrawler/WSDLCrawlerThread.java 

(13:56:08) ~/Desktop/temp → cd multiweb

(13:56:57) ~/Desktop/temp/multiweb → javac ie/moguntia/webcrawler/*.java
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

(13:57:11) ~/Desktop/temp/multiweb → find . -name *.class
./ie/moguntia/threads/ControllableThread.class
./ie/moguntia/threads/MessageReceiver.class
./ie/moguntia/threads/Queue.class
./ie/moguntia/threads/ThreadController.class
./ie/moguntia/webcrawler/PSucker.class
./ie/moguntia/webcrawler/PSuckerThread.class
./ie/moguntia/webcrawler/SaveURL.class
./ie/moguntia/webcrawler/URLQueue.class
./ie/moguntia/webcrawler/WSDLCrawler.class
./ie/moguntia/webcrawler/WSDLCrawlerThread.class

(13:57:18) ~/Desktop/temp/multiweb → java ie.moguntia.webcrawler.PSucker http://www.wikipedia.org test
[0] http://www.wikipedia.org

Answer 2

如果您从外部 ie 目录运行它，它应该可以工作。

注意，一般不建议依赖

CLASSPATH

环境变量；相反，使用

-cp

开关

显式地将类路径放在命令行上