Question

我有一个JSP页面，比如xyz.jsp，我在其中设置了一个会话

request.getSession().setAttribute("path", loc);

在a.java中我成功使用了这个会话并将响应发送回jsp页面，

String fpath = request.getSession().getAttribute("path").toString();

但是，当我在b.java中使用相同的会话值时，我得到空指针异常。

my.jsp-＆gt;按钮点击 - > a.java-＆gt; get session1-＆gt;发送回复my.jsp-＆gt; my.jsp reloads-＆gt; b.java尝试使用session1- ＆GT; NullPointerExceptionError

我试过了，

使用不同的会话变量

session.setAttribute("session1", loc);
session.setAttribute("session2", loc);

在a.java中创建一个新的会话变量并在b.java中访问该变量

仍有同样的错误。

my.jsp看起来像，

String loc = "/u/poolla/workspace/FirstServlet/WebContent/WEB-INF/" + ip +"/" +timeStamp;
session.setAttribute("path", loc);

a.java看起来像

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
{

    HttpSession session = request.getSession();
    String fpath = session.getAttribute("path").toString();


    if(!new File(fpath).exists())
    {
        File uploadedFile = new File(fpath, fileName);
                    item.write(uploadedFile);
        two_file = "Right file " +fileName;
            request.setAttribute("file2", two_file);
        String f2 = "<span class='blue'>" +"Uploaded file " +fileName+ " at " +uploadedFile.getAbsolutePath()+ "<br>" + "</span>";
                    request.setAttribute("f2stat", f2);
    }

RequestDispatcher rd = request.getRequestDispatcher("geco.jsp");
rd.forward(request, response);

b.java看起来像

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
{
    HttpSession session = request.getSession();
    String b = session.getAttribute("path").toString();
            File file = new File(b);
            if(!file.exists())
            {
                file.createNewFile();
            }
            FileWriter fw = new FileWriter(file.getAbsoluteFile());
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write("hi");
            bw.close();
}

Answer 1

这只是为了帮助您解决问题。我的意思是在jsp中使用scriptlet，在这种情况下使用两个servlet的命名约定都不推荐..

代码段

<强>的web.xml

<servlet>
    <servlet-name>myservleta</servlet-name>
    <servlet-class>com.examples.example.MyServletA</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet>
    <servlet-name>myservletb</servlet-name>
    <servlet-class>com.examples.example.MyServletB</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>myservleta</servlet-name>
    <url-pattern>*.do</url-pattern>
</servlet-mapping>

<servlet-mapping>
    <servlet-name>myservletb</servlet-name>
    <url-pattern>*.go</url-pattern>
</servlet-mapping>

<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>

<强>的index.jsp

<body>
    <%
        session.setAttribute("location", "tvm");
    %>
    <form action="gotoajava.do" method="post">
        <input type="Submit" />
    </form>
</body>

<强> page2.jsp

<body>
    <form action="gotobjava.go" method="get">
        <input type="Submit" />
    </form>
</body>

<强> MyServletA.java

protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        String loc = request.getSession().getAttribute("location").toString();
        System.out.println("location in ServletA from session is " + loc);

        RequestDispatcher rd = request.getRequestDispatcher("geco.jsp");
        rd.forward(request, response);
    }

<强> MyServletB.java

protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession session = request.getSession();
        String loc = session.getAttribute("location").toString();
        System.out.println("location in ServletB from session is " + loc);

    }

控制台日志：

Mar 20, 2014 9:28:33 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 343 ms
location in ServletA from session is tvm
location in ServletB from session is tvm

编辑：执行＆＃39; gotobjava.go＆＃39;的jsp;根据OP的编辑请求将操作重命名为page2.jsp

会话显示空错误

1 个答案: