Java類路徑問題

Question

我已經編譯了，現在我正嘗試在ie目錄中使用以下命令從OSX和Fendora中的終端運行此程序：

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

但是我收到以下錯誤：

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)

我之前從未運行過使用命令行中的軟件包的應用程序，因此無法確定錯誤。

我試圖使用export CLASSPATH=.設置類路徑export CLASSPATH=. 這樣就可以將當前目錄添加到類路徑中。

目錄結構如下：

ie/moguntia/webcrawler/

Answer 1

根據編譯類的位置，您需要在java命令中包括此位置，例如，如果它們位於classes目錄中：

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

或如果它們在當前目錄中：

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

要不就

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

這是我運行該文件的方法（將文件解壓縮，cd到目錄，編譯，查找類，運行）：

(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

如果您從ie目錄外部運行它，它應該可以工作。

注意，通常不建議依賴CLASSPATH環境變量。 而是使用-cp開關將classpath明確地放在hte命令行上