请问ERROR:500是什么错误?__java_ShoppingServlet_apache_tomcat_service_

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请问ERROR:500是什么错误?

来源: 互联网发布时间：2015-09-05

本文导语: Location: /music/servlet/shopping.ShoppingServlet Internal Servlet Error: java.lang.NullPointerException at shopping.ShoppingServlet.doPost(ShoppingServlet.java:63) at javax.servlet.http.HttpServlet.service(HttpServlet.java:760) at javax.servlet.http.HttpServlet.service(Http...

Location: /music/servlet/shopping.ShoppingServlet
Internal Servlet Error:

java.lang.NullPointerException
at shopping.ShoppingServlet.doPost(ShoppingServlet.java:63)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:760)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:405)
at org.apache.tomcat.core.Handler.service(Handler.java:287)
at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
at org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:812)
at org.apache.tomcat.core.ContextManager.service(ContextManager.java:758)
at org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:213)
at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:501)
at java.lang.Thread.run(Thread.java:484)

这种类型的错误信息应该从何处着手查错?

有这样几点:
    1.发布文件夹中的类文件与网页文件更新不匹配.(类文件往往旧)
    2.Java文件本身有错.
    3.Tomcat服务配置路径有误.
    4.没有把需要的类文件放到 '发布目录/lib/' 下.

HTTP Responses
An HTTP response contains a result code, header fields, and a body.

The HTTP protocol expects the result code and all header fields to be returned before any body content.

Some commonly used status codes include:

404 - indicates that the requested resource is not available.
401 - indicates that the request requires HTTP authentication.
500 - indicates an error inside the HTTP server which prevented it from fulfilling the request.
503 - indicates that the HTTP server is temporarily overloaded, and unable to handle the request.

500错肯定是程序有问题，错误在ShoppingServlet.java:63行，java.lang.NullPointerException说明ShoppingServlet.java:63行有一个参加操作的变量是NULL

空值

at shopping.ShoppingServlet.doPost(ShoppingServlet.java:63)

取不到值

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