从MySQL读取文本文件

Question

I'm trying to store a text file in a MySQL database, and when needed, save it to a file.

To save the file, I do:

public void saveFile_InDB(File file)
{  
     try {

        String sql = "INSERT INTO sent_emails (fileName, time, clientName) values (?, ?, ?)";
        PreparedStatement statement = conn.prepareStatement(sql);
        statement.setString(1, new Date().toString());
        statement.setString(2, new Date().toString());

        InputStream inputStream = new FileInputStream(file); 
        statement.setBinaryStream(3, inputStream);

        int row = statement.executeUpdate();
        if (row > 0) {
            System.out.println("File saved sucessfully.");
        }
        conn.close();

    } catch (SQLException ex) {
        ex.printStackTrace();
    } catch (IOException ex) {
        ex.printStackTrace();
    }
}

And to retreive and save the file:

public void retrieveFile_fromDB()
{
     try {

         Statement stmt = (Statement) conn.createStatement();
         ResultSet res = stmt.executeQuery("SELECT * FROM sent_emails WHERE clientName='sally'");
         FileOutputStream fos = new FileOutputStream("file.txt");  

         if (res.next()) {

             Blob File = (Blob) res.getBlob("fileName");
             InputStream is = File.getBinaryStream();
             int b = 0;

             while ((b = is.read()) != -1) {
                 fos.write(b);   
             }

             fos.flush();

         }
     } catch (IOException e) {
         e.getMessage (); e.printStackTrace(); 
         System.out.println(e); 
     } catch (SQLException e) {
         e.getMessage (); e.printStackTrace(); 
         System.out.println(e); 
     }
}

Storing the file works, but when I try to retrieve and save it, nothing is stored in the output file?

Answer 1

if you want read file from db Mysql change this part in your code

  Blob File = (Blob) res.getBlob("fileName");
         InputStream is = File.getBinaryStream();
         int b = 0;

         while ((b = is.read()) != -1) {
             fos.write(b);   
         }

         fos.flush();

use this code read array of bytes

    byte [] bs=res.getBytes("fileName");
    fos.write(bs);

it will work if you return multiple files from db you must declare

 FileOutputStream fos = new FileOutputStream("file.txt");

inside while loop and change name of file to avoid overriding

Answer 2

You do not seem to put into the database the things that the column names describe?

fileName and time are for example both set to a timestamp, and clientName is set to the contents of the file. When you later try to select based on clientName , you are actually selecting based on the contents of the file.

Furthermore, when reading the data, you are reading the blob data from the column fileName , but this is wrong because:

1. fileName contains new Date().toString() , not the contents of the file
2. fileName should surely contain the file's name , not its contents?