Write data from Database to File in Java

Question

I am trying to write data from a database into a text file.

The text file remains empty. I tried to deg. Here is the code:

public void writeText()
{
     try
    {
        Class.forName("com.mysql.jdbc.Driver");
    }
    catch(Exception e)
    {
        e.printStackTrace();
    }
    final String DB_URL ="jdbc:mysql://mis-sql.uhcl.edu/gattupalliv3940";
    Connection conn = null;
    Statement stat  = null;
    ResultSet rs = null;
    try
    {
        conn = DriverManager.getConnection(DB_URL,"gattupalliv3940","1552688");
        stat = conn.createStatement();
        rs = stat.executeQuery("select * from student_2");
        FileWriter fw = new FileWriter("data.txt");
        BufferedWriter bw = new BufferedWriter(fw);
        String line ="";
        while(rs.next())
        {
            line = rs.getInt(1)+"\t"+rs.getString(2)+"\t"+rs.getDouble(3);
            bw.write(line);
            bw.newLine();
        }
        bw.close();
    }
    catch(Exception e)
    {
        e.printStackTrace();
    }
    finally
    {
        try
        {
            conn.close();
            rs.close();
            stat.close();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
}

Answer 1

If you aren't getting any errors and the file is empty, the only thing that can be happening is your while(rs.next()) line must be returning false the first time through; meaning you aren't getting anything from the database.

Have you stepped through the code to verify which lines are executing and which ones are not?

I suspect that the file isn't being written to where you expect since you aren't specifying a directory. I created a simple test and the file was written out to the Tomcat's directory at ...\\springsource\\vfabric-tc-server-developer-2.6.4.RELEASE\\spring-insight-instance\\wtpwebapps\\Junk\\data.txt (my Project is named Junk). Below is my code (without the database stuff):

@RequestMapping(value="/")
public ModelAndView test(HttpServletRequest request, HttpServletResponse response) throws IOException{

    writeText(request.getRealPath("data.txt"));

    return new ModelAndView("home");
}

public void writeText(String path) {
    BufferedWriter bw = null;
    try {
        FileWriter fw = new FileWriter(path);
        bw = new BufferedWriter(fw);
        String line = "this is only a test";
        bw.write(line);
        bw.newLine();
    }
    catch(Exception e) {
        e.printStackTrace();
    } finally {
        if( bw != null ) {
            try {
                bw.close();
            } catch (IOException e) {
                // ignore
            }
        }
    }
}

Answer 2

In here can use library called JOConnection. import this library to your project externally.

In the beginning create a file.

 File myDb=new File("file_name");

then access that file db by using this code

 Database db=Connection.openConnection(myDb);

then get data to write to db as list of objects.

 ArrayList<Items> itmDetails=  (ArrayList<Items> )db.getList("Items");

then add those data to the file db

       db.addList("Items", itmDetails);

finally

  Connection.save(); 

Answer 3

I have the exact same problem when trying to write log to a file from Oracle.

FileOutputStream works for me! Hopefully this works for you. I have no idea why is PrintWriter not working. Must be setup of oracle...

List<String> logs = new LinkedList<String>();       
String filepath = "xxx.txt";
System.out.println(filepath);
OutputStream os = null;
try{
    for(int i = 0; i < logs.size(); i++) {
        os = new FileOutputStream(filepath,true);
        os.write(("\n"+logs.get(i)).getBytes(), 0, ("\n"+logs.get(i)).length());            
    }               
    } catch (IOException e) {
         e.printStackTrace();
    } finally{
         try {
             os.close();
         } catch (IOException e) {
             e.printStackTrace();
     }
}