read the contents of a file upload in java

I know how to upload a file:

<html>
<head>
<title>File Uploading Form</title>
</head>
<body>

<form action="UploadServlet" method="post"
                        enctype="multipart/form-data">

File :<input type="file" name="file" size="50" />

<input type="submit" value="Upload File"/>


</form>
</body>
</html>

This is the class for reading the file:

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class BufferedReaderExample {

    public static void main(String[] args) {

        try (BufferedReader br = new BufferedReader(new FileReader("C:\\testing.txt")))
        {

            String sCurrentLine;

            while ((sCurrentLine = br.readLine()) != null) {
                System.out.println(sCurrentLine);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } 

    }
}

Now how do you link both these together. The user uploads the file onto the server and the server processes it. i.e., it accepts the file and prints it contents. Can I use struts framework for this? I want to upload excel sheet and print the contents to the jsp page. I have the code for reading the excel sheet in java using apache poi. But the path to read the excel file is hard coded. how do you take it from the uploaded file?

This is the file for reading excel sheet:

public class ReadExcelDemo
{
    public static void main(String[] args)
    {
        try
        {
            FileInputStream file = new FileInputStream(new File("howtodoinjava_demo.xlsx"));

            //Create Workbook instance holding reference to .xlsx file
            XSSFWorkbook workbook = new XSSFWorkbook(file);

            //Get first/desired sheet from the workbook
            XSSFSheet sheet = workbook.getSheetAt(0);

            //Iterate through each rows one by one
            Iterator<Row> rowIterator = sheet.iterator();
            while (rowIterator.hasNext())
            {
                Row row = rowIterator.next();
                //For each row, iterate through all the columns
                Iterator<Cell> cellIterator = row.cellIterator();

                while (cellIterator.hasNext())
                {
                    Cell cell = cellIterator.next();
                    //Check the cell type and format accordingly
                    switch (cell.getCellType())
                    {
                        case Cell.CELL_TYPE_NUMERIC:
                            System.out.print(cell.getNumericCellValue() + "t");
                            break;
                        case Cell.CELL_TYPE_STRING:
                            System.out.print(cell.getStringCellValue() + "t");
                            break;
                    }
                }
                System.out.println("");
            }
            file.close();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

Output:

ID NAME LASTNAME 1.0 Amit Shukla 2.0 Lokesh Gupta
3.0 John Adwards 4.0 Brian Schultz

But how do you stitch the uploaded and the servlet file together. How do you read the uploaded file?

标签： java file-upload apache-poi struts

3条回答

女痞

2楼-- · 2019-04-29 12:27

You can achieve it by breaking whole process in two steps

1) Upload file

boolean isMultipart = ServletFileUpload.isMultipartContent(request);

        if (!isMultipart) {
            return;
        }

        // Create a factory for disk-based file items
        DiskFileItemFactory factory = new DiskFileItemFactory();

        // Sets the size threshold beyond which files are written directly to
        // disk.
        factory.setSizeThreshold(MAX_MEMORY_SIZE);

        // Sets the directory used to temporarily store files that are larger
        // than the configured size threshold. We use temporary directory for
        // java
        factory.setRepository(new File(System.getProperty("java.io.tmpdir")));

        // constructs the folder where uploaded file will be stored
        String uploadFolder = getServletContext().getRealPath("")
                + File.separator + DATA_DIRECTORY;

        // Create a new file upload handler
        ServletFileUpload upload = new ServletFileUpload(factory);

        // Set overall request size constraint
        upload.setSizeMax(MAX_REQUEST_SIZE);

        try {
            // Parse the request
            List items = upload.parseRequest(request);
            Iterator iter = items.iterator();
            while (iter.hasNext()) {
                FileItem item = (FileItem) iter.next();

                if (!item.isFormField()) {
                    String fileName = new File(item.getName()).getName();
                    String filePath = uploadFolder + File.separator + fileName;
                    File uploadedFile = new File(filePath);
                    System.out.println(filePath);
                    // saves the file to upload directory
                    item.write(uploadedFile);
                }
            }

            // displays done.jsp page after upload finished
            getServletContext().getRequestDispatcher("/done.jsp").forward(
                    request, response);

        } catch (FileUploadException ex) {
            throw new ServletException(ex);
        } catch (Exception ex) {
            throw new ServletException(ex);
        }

2) After upload pass file location to the method which read file data using apche poi. Use File uploadedFile = new File(filePath); object to get file location.

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Anthone

3楼-- · 2019-04-29 12:27

Like many operations in Java, reading a file upload is unneccessarily complex, and difficult to work out from the javadocs. You are already planning to use Apache libraries to read your uploaded file, so I recommend using apache.commons.fileupload to upload your file as well.

This code fragment uploads a CSV file into a string:

...

import org.apache.commons.fileupload.*;
import org.apache.commons.fileupload.disk.*; 
import org.apache.commons.fileupload.servlet.*;

...

  if (ServletFileUpload.isMultipartContent(request)) {
    int i=0;

    DiskFileItemFactory factory = new DiskFileItemFactory();
    // files smaller than 5MB will be held in memory
    factory.setSizeThreshold(5000000); 

    ServletFileUpload upload = new ServletFileUpload(factory);
    upload.setFileSizeMax(10000000); // max size of attachment 10MB

    List list = upload.parseRequest(request);
    Iterator iter = list.iterator();

    String csv = null;

    while (iter.hasNext()) {            
      FileItem param = (FileItem)iter.next();
      if (!param.isFormField()) { 
        csv = param.getString();
        break;
      }
    }

    if (csv==null) {
      throw new Exception("CSV buffer not uploaded");
    }
  }

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傲

4楼-- · 2019-04-29 12:52

I got it. The index file(html) is for uploading the file (as above in my qquestion) The java class for it is:

import java.io.*;
import java.util.*;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.output.*;

public class UploadServlet extends HttpServlet {

   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>");
      String fileName = "";
      while ( i.hasNext () ) 
      {
         FileItem fi = (FileItem)i.next();
         if ( !fi.isFormField () )  
         {
            // Get the uploaded file parameters
            String fieldName = fi.getFieldName();
             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( filePath + 
               fileName.substring( fileName.lastIndexOf("\\"))) ;
            }else{
               file = new File( filePath + 
               fileName.substring(fileName.lastIndexOf("\\")+1)) ;
            }
            fi.write( file ) ;
            out.println("Uploaded Filename: " + fileName + "<br>");
            out.println("Uploaded in location: "+filePath);
         }
      }
      out.println("</body>");
      out.println("</html>");
      ReadExcelDemo rd = new ReadExcelDemo();
      System.out.println("file name: "+fileName.substring(fileName.lastIndexOf("\\")));
      String s = fileName.substring(fileName.lastIndexOf("\\"));
      System.out.println(filePath);
      System.out.println(s);
      String fileP = filePath.concat(s+"\\");

      System.out.println(fileP);
      rd.read(fileP);

   }catch(Exception ex) {
       System.out.println(ex);
   }
   }
   public void doGet(HttpServletRequest request, 
                       HttpServletResponse response)
        throws ServletException, java.io.IOException {

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

This is the class for reading the excel sheet using apache poi jars:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.Iterator;

import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class ReadExcelDemo { 
    public static void read(String filePath)  {
//  public static void main(String[] args){
 try {           
     FileInputStream file = new FileInputStream(new File(filePath));  
//   FileInputStream file = new FileInputStream(new File("C:\\work\\demo.xlsx"));
    //Create Workbook instance holding reference to .xlsx file  
    XSSFWorkbook workbook = new XSSFWorkbook(file); 
    //Get first/desired sheet from the workbook
    XSSFSheet sheet = workbook.getSheetAt(0);
    //Iterate through each rows one by one  
    Iterator<Row> rowIterator = sheet.iterator();   
    while (rowIterator.hasNext()) {            
        Row row = rowIterator.next();
        //For each row, iterate through all the columns  
        Iterator<Cell> cellIterator = row.cellIterator();   
        while (cellIterator.hasNext())  {               
            Cell cell = cellIterator.next();    
            //Check the cell type and format accordingly   
            switch (cell.getCellType())                     {        
                case Cell.CELL_TYPE_NUMERIC:  System.out.print(cell.getNumericCellValue() + "\t"); 
            break;                       
                case Cell.CELL_TYPE_STRING: System.out.print(cell.getStringCellValue() + "\t");  
            break;     
            }           
        }             
        System.out.println("");         
    }  
/*  int row=0;
    int k=1;
    Row myRow = sheet.createRow ((short)row);
     myRow.createCell(k).setCellValue ("new data"); 
      myRow = sheet.createRow ((short)row++); */
//  Cell cell1 = sheet.   // Access the second cell in second row to update the value

  //  cell1.setCellValue("OverRide Last Name");

     Cell cell1 = null; // declare a Cell object

     cell1 = sheet.getRow(2).getCell(2);   // Access the second cell in second row to update the value

     cell1.setCellValue("OverRide Last Name");


    file.close();
/*  FileOutputStream out = new FileOutputStream(new File("write_demo1.xlsx"));
    workbook.write(out);  
    out.close(); */
    }
    catch (Exception e) {      
        e.printStackTrace();   
        }
    }
 }

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