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处理文件上传时出现java.lang.NullPointerException

发布于 2025-01-06 07:28:56 字数 8312 浏览 1 评论 0原文

如果您能找到我的问题所在以及如何解决它，我将非常感激。 (java.lang.NullPointerException)

这是我的 html，从中我获得一个文本字段，并在此 servlet 中上传 2 个文件

index.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 
    <title>Insert title here</title>
    </head>
    <body>
    <h3>File Upload:</h3>
    <form action="UploadServlet" method="post"
                            enctype="multipart/form-data">
    <br><br><br><br><br>
    Insert your ID (marca) - ex: 101358 
    <br>
    <input type="text" name="rid" size="40" />
    <br><br>
    Browse your files:
    <br>
    <input type="file" name="file" size="30" />
    <br />
    <br/>
    <input type="file" name="file" size="30" />
    <br />
    <br>
    <input type="submit" value="Upload File" />
    </form>
    </body>
    </html>

我将上传的文件保存到特定文件夹中，然后进行连接到一个数据库，我想存储从 html 获取的字符串和上传文件的文件路径

UploadServlet.java

public class UploadServlet extends HttpServlet {

  /**
   * 
   */
  private static final long serialVersionUID = 1L;
  private boolean isMultipart;
  private String filePath;
  private int maxFileSize = 50 * 1024;
  private int maxMemSize = 4 * 1024;
  private File file ;

  public void init( ){
    // Get the file location where it would be stored.
    filePath = getServletContext().getInitParameter("file-upload"); 
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, java.io.IOException {
    // Check that we have a file upload request
    isMultipart = ServletFileUpload.isMultipartContent(request);
    response.setContentType("text/html");
    java.io.PrintWriter out = response.getWriter( );
    if( !isMultipart ){
      out.println("<html>");
      out.println("<head>");
      out.println("<title>Servlet upload</title>");  
      out.println("</head>");
      out.println("<body>");
      out.println("<p>No file uploaded</p>"); 
      out.println("</body>");
      out.println("</html>");
      return;
    }
    DiskFileItemFactory factory = new DiskFileItemFactory();
    // maximum size that will be stored in memory
    factory.setSizeThreshold(maxMemSize);
    // Location to save data that is larger than maxMemSize.
    factory.setRepository(new File("c:\\temp"));

    // Create a new file upload handler
    ServletFileUpload upload = new ServletFileUpload(factory);
    // maximum file size to be uploaded.
    upload.setSizeMax( maxFileSize );

    try{ 
      // Parse the request to get file items.
      List fileItems = upload.parseRequest(request);

      // Process the uploaded file items
      Iterator i = fileItems.iterator();

      out.println("<html>");
      out.println("<head>");
      out.println("<title>Servlet upload</title>");  
      out.println("</head>");
      out.println("<body>");
      //while ( i.hasNext () ) 
      //{
      FileItem fi = (FileItem)i.next();
      if ( !fi.isFormField () )  
        {
          // Get the uploaded file parameters
          //String fieldName = fi.getFieldName();
          String fileName = fi.getName();
          //String contentType = fi.getContentType();
          //boolean isInMemory = fi.isInMemory();
          //long sizeInBytes = fi.getSize();
          // Write the file
          if( fileName.lastIndexOf("\\") >= 0 ){
            file = new File( "C:/UploadedFiles/" + fileName.substring( fileName.lastIndexOf("\\"))) ;
          }else{
            file = new File( "C:/UploadedFiles/" + fileName.substring(fileName.lastIndexOf("\\")+1)) ;
          }
          fi.write( file ) ;
          out.println("Uploaded Filename: " + fileName + " --- saved in C:/UploadedFiles/ " + "<br>");
        }

      FileItem fi2 = (FileItem)i.next();
      if ( !fi2.isFormField () ) 
        {
          // Get the uploaded file parameters
          //String fieldName2 = fi2.getFieldName();
          String fileName2 = fi2.getName();
          //String contentType2 = fi2.getContentType();

          //boolean isInMemory = fi2.isInMemory();
          //long sizeInBytes = fi2.getSize();
          // Write the file
          if( fileName2.lastIndexOf("\\") >= 0 ){
            file = new File( "C:/UploadedFiles/" + fileName2.substring( fileName2.lastIndexOf("\\"))) ;
          }else{
            file = new File( "C:/UploadedFiles/" + fileName2.substring(fileName2.lastIndexOf("\\")+1)) ;
          }
          fi2.write( file ) ;
          out.println("Uploaded Filename: " + fileName2 + " --- saved in C:/UploadedFiles/ " + "<br>");       
        }

      //}
      out.println("</body>");
      out.println("</html>");     
      String idmarca = request.getParameter("rid");

      String itemName1 = fi.getName();
      String path1 = new String("C:\\UploadedFiles\\" + itemName1.substring(itemName1.lastIndexOf("\\")));

      String itemName2 = fi2.getName();
      String path2 = new String("C:\\UploadedFiles\\" + itemName2.substring(itemName2.lastIndexOf("\\")));
      Connection con = null;
      PreparedStatement ps; 

      try{      
        String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
        Class.forName(driver);
        String db = "jdbc:odbc:upload";
        con = DriverManager.getConnection(db, "", "");  
        String sql = "INSERT INTO file1(marca,file1,file2) VALUES(?, ?, ?)";            
        ps = con.prepareStatement(sql);              

        ps.setString(1, idmarca);
        ps.setString(2, path1);
        ps.setString(3, path2);
        int s = ps.executeUpdate();
        if(s>0){
          System.out.println("Uploaded successfully !");
        }
        else{
          System.out.println("Error!");
        }

      }
      catch(Exception e){
        e.printStackTrace();
      }
      finally {
        // close all the connections.
        //ps.close();
        //con.close();
      }
    }catch(Exception ex) {
      ex.printStackTrace();
    }  
  }   


  public void doGet(HttpServletRequest request, 
                    HttpServletResponse response)
    throws ServletException, java.io.IOException {

    throw new ServletException("GET method used with " + getClass( ).getName( )+": POST method required.");
  } 
}

java.lang.NullPointerException
    at UploadServlet.doPost(UploadServlet.java:126)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:307)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:619)
原文

I would be very gratefull if you could find where is my problem and how can I fix it. (java.lang.NullPointerException)

here is my html from where I get a textfield and I upload 2 files

index.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 
    <title>Insert title here</title>
    </head>
    <body>
    <h3>File Upload:</h3>
    <form action="UploadServlet" method="post"
                            enctype="multipart/form-data">
    <br><br><br><br><br>
    Insert your ID (marca) - ex: 101358 
    <br>
    <input type="text" name="rid" size="40" />
    <br><br>
    Browse your files:
    <br>
    <input type="file" name="file" size="30" />
    <br />
    <br/>
    <input type="file" name="file" size="30" />
    <br />
    <br>
    <input type="submit" value="Upload File" />
    </form>
    </body>
    </html>

in this servlet I save the uploaded files into a specific folder and after that I am connecting to a database where I want to store the string got from html and the file paths from the uploaded files

UploadServlet.java

public class UploadServlet extends HttpServlet {

  /**
   * 
   */
  private static final long serialVersionUID = 1L;
  private boolean isMultipart;
  private String filePath;
  private int maxFileSize = 50 * 1024;
  private int maxMemSize = 4 * 1024;
  private File file ;

  public void init( ){
    // Get the file location where it would be stored.
    filePath = getServletContext().getInitParameter("file-upload"); 
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, java.io.IOException {
    // Check that we have a file upload request
    isMultipart = ServletFileUpload.isMultipartContent(request);
    response.setContentType("text/html");
    java.io.PrintWriter out = response.getWriter( );
    if( !isMultipart ){
      out.println("<html>");
      out.println("<head>");
      out.println("<title>Servlet upload</title>");  
      out.println("</head>");
      out.println("<body>");
      out.println("<p>No file uploaded</p>"); 
      out.println("</body>");
      out.println("</html>");
      return;
    }
    DiskFileItemFactory factory = new DiskFileItemFactory();
    // maximum size that will be stored in memory
    factory.setSizeThreshold(maxMemSize);
    // Location to save data that is larger than maxMemSize.
    factory.setRepository(new File("c:\\temp"));

    // Create a new file upload handler
    ServletFileUpload upload = new ServletFileUpload(factory);
    // maximum file size to be uploaded.
    upload.setSizeMax( maxFileSize );

    try{ 
      // Parse the request to get file items.
      List fileItems = upload.parseRequest(request);

      // Process the uploaded file items
      Iterator i = fileItems.iterator();

      out.println("<html>");
      out.println("<head>");
      out.println("<title>Servlet upload</title>");  
      out.println("</head>");
      out.println("<body>");
      //while ( i.hasNext () ) 
      //{
      FileItem fi = (FileItem)i.next();
      if ( !fi.isFormField () )  
        {
          // Get the uploaded file parameters
          //String fieldName = fi.getFieldName();
          String fileName = fi.getName();
          //String contentType = fi.getContentType();
          //boolean isInMemory = fi.isInMemory();
          //long sizeInBytes = fi.getSize();
          // Write the file
          if( fileName.lastIndexOf("\\") >= 0 ){
            file = new File( "C:/UploadedFiles/" + fileName.substring( fileName.lastIndexOf("\\"))) ;
          }else{
            file = new File( "C:/UploadedFiles/" + fileName.substring(fileName.lastIndexOf("\\")+1)) ;
          }
          fi.write( file ) ;
          out.println("Uploaded Filename: " + fileName + " --- saved in C:/UploadedFiles/ " + "<br>");
        }

      FileItem fi2 = (FileItem)i.next();
      if ( !fi2.isFormField () ) 
        {
          // Get the uploaded file parameters
          //String fieldName2 = fi2.getFieldName();
          String fileName2 = fi2.getName();
          //String contentType2 = fi2.getContentType();

          //boolean isInMemory = fi2.isInMemory();
          //long sizeInBytes = fi2.getSize();
          // Write the file
          if( fileName2.lastIndexOf("\\") >= 0 ){
            file = new File( "C:/UploadedFiles/" + fileName2.substring( fileName2.lastIndexOf("\\"))) ;
          }else{
            file = new File( "C:/UploadedFiles/" + fileName2.substring(fileName2.lastIndexOf("\\")+1)) ;
          }
          fi2.write( file ) ;
          out.println("Uploaded Filename: " + fileName2 + " --- saved in C:/UploadedFiles/ " + "<br>");       
        }

      //}
      out.println("</body>");
      out.println("</html>");     
      String idmarca = request.getParameter("rid");

      String itemName1 = fi.getName();
      String path1 = new String("C:\\UploadedFiles\\" + itemName1.substring(itemName1.lastIndexOf("\\")));

      String itemName2 = fi2.getName();
      String path2 = new String("C:\\UploadedFiles\\" + itemName2.substring(itemName2.lastIndexOf("\\")));
      Connection con = null;
      PreparedStatement ps; 

      try{      
        String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
        Class.forName(driver);
        String db = "jdbc:odbc:upload";
        con = DriverManager.getConnection(db, "", "");  
        String sql = "INSERT INTO file1(marca,file1,file2) VALUES(?, ?, ?)";            
        ps = con.prepareStatement(sql);              

        ps.setString(1, idmarca);
        ps.setString(2, path1);
        ps.setString(3, path2);
        int s = ps.executeUpdate();
        if(s>0){
          System.out.println("Uploaded successfully !");
        }
        else{
          System.out.println("Error!");
        }

      }
      catch(Exception e){
        e.printStackTrace();
      }
      finally {
        // close all the connections.
        //ps.close();
        //con.close();
      }
    }catch(Exception ex) {
      ex.printStackTrace();
    }  
  }   


  public void doGet(HttpServletRequest request, 
                    HttpServletResponse response)
    throws ServletException, java.io.IOException {

    throw new ServletException("GET method used with " + getClass( ).getName( )+": POST method required.");
  } 
}

java.lang.NullPointerException
    at UploadServlet.doPost(UploadServlet.java:126)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:307)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:619)

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评论（1）

情愿 2025-01-13 07:28:56

好的，我的问题出在 String idmarca = request.getParameter("rid"); 行中它从 html 文本字段获取文本。在添加此文本字段之前，我能够保存上传文件的文件路径。

当使用multipart/form-data请求时，表单数据部分不是通过 request.getParameter() 可用作请求参数。它们只能通过 request.getPart() 作为表单数据部分使用。但是，当您使用 Apache Commons FileUpload（也许您还没有使用新的 Servlet 3.0 版本，其中 getPart() 方法可用）时，那么您实际上应该使用相同的 API 来检索文本字段值。

继续迭代 fileItems。文本字段值就在那里。

另请参阅：

OK, my problem is in line String idmarca = request.getParameter("rid"); it gets the text from the html textfield. Before adding this textfield I was able to save the file paths of the uploaded files.

When using multipart/form-data requests, the form data pars are not available as request parameters by request.getParameter(). They are only available as form data parts by request.getPart(). But as you're using Apache Commons FileUpload (perhaps you aren't using the new Servlet 3.0 version yet wherein the getPart() method is available), then you should actually be using the very same API to retrieve the text field value.

Continue iterating the fileItems. The text field value is in there.

See also:

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