Question

我有一个Web应用程序，其中包含一些以前在Linux机器上运行的JSP。我需要在运行Tomcat 5.5.29的Windows XP SP3机器上运行它。大多数现在都在运行但是这一项：该应用程序能够将配置文件写入其Windows目录（即C：\ Program Files \ Apache \ Tomcat \ webapps \ myapp）。但是当它尝试这样做时，应用程序无法打开FileOutputStream（返回null）。如果我删除路径说明符，只是让它打开文件，它就会在Tomcat目录中成功打开它。

第一行失败，但第二行成功：

//  outputFile2 = new PrintWriter(new FileOutputStream(basePathName + "programAll.txt", false));
    outputFile2 = new PrintWriter(new FileOutputStream("programAll.txt", false));

以下是创建basePathName的代码：

    String basePathName = getBaseFilePath();  
    ...
    public String getBaseFilePath()
            {
            String curDir = System.getProperty("catalina.home");  
            curDir = curDir + "/webapps/pubmed/"; 
            curDir = "file:///" + formatPathNameForOS(curDir);
            return curDir;
            }

   public String formatPathNameForOS(String pathName)
        {
        if (codeIsOnWindows())
            {
            pathName = pathName.replace('/','\\');
            }
        else
            {
            pathName = pathName.replace('\\','/');
            }
        return pathName;
    }

以下是异常消息：

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:460)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:373)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:321)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:257)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
root cause

java.lang.NullPointerException
    org.apache.jsp.updateMemberLists_jsp._jspService(updateMemberLists_jsp.java:1492)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:321)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:257)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)

这是堆栈跟踪：

Aug 6, 2010 1:20:39 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at org.apache.jsp.updateMemberLists_jsp._jspService(updateMemberLists_jsp.java:1492)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:321)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:257)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
    at org.globus.tomcat.coyote.valves.HTTPSValve55.invoke(HTTPSValve55.java:45)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:873)
    at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
    at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
    at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
    at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
    at java.lang.Thread.run(Thread.java:595)

我查看了updateMembersLists_jsp.java，这里是空指针发生的部分：

//create a file to write to the output
PrintWriter outputFile2 = null;
try
    {
    outputFile2 = new PrintWriter(new FileOutputStream(basePathName + "programAll.txt", false));
//  outputFile2 = new PrintWriter(new FileOutputStream("programAll.txt", false));
    }
    catch (FileNotFoundException e)
        {
        out.write("<p><font color='red'>Error Saving</font></p>");
        }
outputFile2.print(output);  // THIS IS LINE 1492 -- NULL POINTER
outputFile2.close();

另外：我们现在正在运行Tomcat而不是Program Files。我检查了basePathName并正确计算它。

现在我发现可能需要调整Tomcat的策略设置。我在catalina.policy中添加了以下几行，希望它能正确设置：

// The permissions granted to the pubmed webapp
grant codeBase "file:${catalina.home}/webapps/pubmed/-" {
        permission java.io.FilePermission "${catalina.home}/webapps/pubmed/-", "read, write";
        permission java.io.FilePermission "${catalina.home}/webapps/pubmed/*", "read, write";
};

这似乎没有任何效果。运行tomcat的Windows用户对pubmed目录具有读/写权限。除了这个webapp将文件写入自己的目录似乎有问题之外，我还缺少什么？

肖恩

Answer 1

您不应在Java IO中使用相对路径。路径将相对于当前工作目录，这取决于您启动webserver / webapplication的方式。例如，当在Eclipse中启动Tomcat时，它可能是Eclipse项目目录。当Tomcat从CMD启动时，它可能是CMD中当前打开的文件夹。当Tomcat作为服务启动时，它可能是Tomcat的/bin文件夹。要自己确定，请执行以下操作：

System.out.println(new File("programAll.txt").getAbsolutePath());

你会发现它与你期望的完全不同。

您需要指定绝对路径。您可以使用ServletContext#getRealPath()将webcontent相对路径转换为绝对磁盘文件系统路径。

String relativeWebPath = "programAll.txt";
String absoluteDiskPath = getServletContext().getRealPath(relativeWebPath);
output = new FileOutputStream(absoluteDiskPath);
// ...

每个servlet中都有getServletContext()方法。

那就是说，你是否考虑过每次重新部署/重启webapp / server时都会擦除/覆盖webcontent中的所有修改过的文件？如果您想要更多永久存储，我强烈建议将它们存储在外部 webcontent（当然是绝对路径，例如/var/webapp/files左右）。

Answer 2

尝试以下列方式获取路径：

String path = getServletContext().getRealPath("/");

这会将您的路径（到您的webapp）转换为磁盘上的实际路径。

设置JSP / Tomcat / Windows的目录权限

2 个答案: