java.lang.NoClassDefFoundError：從AIX運行時出現javax.mail.Address錯誤

Question

我想在我的AIX服務器上運行一個java程序。我寫了類路徑

/usr/java6/bin/javac -classpath :.:/usr/jdk/commons-net-3.0.1.jar:/usr/jdk/classes12.jar:/usr/jdk/mysql-connector-java-5.1.17-bin.jar:/usr/jdk/jtds-1.2.5.jar:/urs/jdk/mail.jar:/usr/jdk/joda-time-1.6.2.jar:/usr/jdk/commons-codec-1.4.jar:/usr/jdk/commons-logging-1.1.1.jar:/usr/jdk/httpclient-4.1.1.jar:/usr/jdk/httpclient-cache-4.1.1.jar:/usr/jdk/httpcore-4.1.jar:/usr/jdk/httpmime-4.1.1.jar:/usr/jdk/mailapi.jar:/usr/jdk/pop3.jar:/usr/jdk/smtp.jar:/usr/jdk/dsn.jar:/usr/jdk/imap.jar -d . *.java 

這似乎編譯正確。然後，當我運行程序

java daily_transmission 

我得到的錯誤java.lang.NoClassDefFoundError：javax.mail.Address。所有在Eclipse中工作之前的.jar文件都位於/ usr/jdk文件中。

Answer 1

一個NoClassDefFoundError意味着（quoting the relevant JavaDoc)：

Thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found.

The searched-for class definition existed when the currently executing class was compiled, but the definition can no longer be found.

兩件事情來檢查：

1. 首先，你似乎在你的classpath中有一個錯字（儘管它不能一直當你編譯代碼時，或者它不會編譯成功，所以這顯然不是你所看到的異常的根本原因。）：

   /urs/jdk/mail.jar 
   

   應該

   /usr/jdk/mail.jar 
   

2. 確保您還使用-classpath選項傳遞classpath以java以及爲javac在運行時拿起這些.jar文件：

   java -classpath :.:/usr/jdk/commons-net-3.0.1.jar:/usr/jdk/classes12.jar:/usr/jdk/mysql-connector-java-5.1.17-bin.jar:/usr/jdk/jtds-1.2.5.jar:/urs/jdk/mail.jar:/usr/jdk/joda-time-1.6.2.jar:/usr/jdk/commons-codec-1.4.jar:/usr/jdk/commons-logging-1.1.1.jar:/usr/jdk/httpclient-4.1.1.jar:/usr/jdk/httpclient-cache-4.1.1.jar:/usr/jdk/httpcore-4.1.jar:/usr/jdk/httpmime-4.1.1.jar:/usr/jdk/mailapi.jar:/usr/jdk/pop3.jar:/usr/jdk/smtp.jar:/usr/jdk/dsn.jar:/usr/jdk/imap.jar daily_transmission 
   

Answer 2

NoClassDefFoundError表示ClassLoader能夠找到該類，但無法加載。這通常發生在違規類中的某個靜態字段無法初始化時。所以我相信你的類路徑可能是正確的;但該類中的某些靜態字段無法正確設置。