Question

I am trying to build a servlet that parses form input and creates a .csv file from them, but the bufferedWriter object truncates a lot of characters for no (apparent to me) reason.

        String filepath = getServletContext().getRealPath("\\") + "temp";
        String filename = "csv"+dateFormat.format(date)+".csv";
        File file = new File(filepath + filename);            
        file.createNewFile();
        BufferedWriter fwrite = new BufferedWriter(new FileWriter(file));
        for(int i=0; i<list.size(); i++) {
            String[] dataEntry = list.get(i);
            for (int j=0; j<dataEntry.length;j++)                 
                 fwrite.write("test1-2");
                //fwrite.append(dataEntry[j]+";");     
            fwrite.newLine();
        }
        fwrite.close();            
         URI fileUri = file.toURI();
         stream = response.getOutputStream();
         response.setContentType("text/csv");
         response.addHeader("Content-Disposition", "attachment; filename="
            + filename);

         URLConnection urlConn = fileUri.toURL().openConnection();
         response.setContentLength((int) urlConn.getContentLength());
         buf = new  BufferedInputStream(urlConn.getInputStream());                          
         while (buf.read() != -1)
            stream.write(buf.read());
        } finally {
        if (stream != null)
            stream.close();
        if (buf != null)
            buf.close();     
        }          
}

Sorry if the code is a bit slapdash. My current output when writing the “test1-2” string for each entry is

et-ts12et-ts12et-ts12ÿ

any further comments on the code itself would be appreciated I’m just experimenting with stuff i find on the net, I have no actual best practices points of reference.

Answer 1

I’d maybe add a few methods so that no individual method is overly large. For example:

/**
 * Saves the List of String[] to the File.
 * 
 * @param f
 * @param list
 * 
 * @throws IOException
 */
void saveList(File f, List<String[]> list) throws IOException {
    FileWriter fw = null;
    try {
        fw = new FileWriter(f);
        saveList(fw, list);
    } finally {
        if (null != fw) {
            // Ensure that fw is closed.
            fw.close();
        }
    }
}

/**
 * Saves the List of String[] to the Writer.
 * 
 * @param w
 * @param list
 * 
 * @throws IOException
 */
void saveList(Writer w, List<String[]> list) throws IOException {
    BufferedWriter bw = new BufferedWriter(w);
    for (int i = 0; i < list.size(); i++) {
        String[] dataEntry = list.get(i);
        for (int j = 0; j < dataEntry.length; j++) {
            bw.write("test1-2");
            // bw.append(dataEntry[j]+";");
        }
        bw.newLine();
    }
    bw.flush();
}

/**
 * Copies in's contents to out.
 * 
 * @param in
 *            Must not be null.
 * @param out
 *            Must not be null.
 * 
 * @throws IOException
 */
void copyStream(InputStream in, OutputStream out) throws IOException {
    if (null == in) {
        throw new NullPointerException("in must not be null");
    }
    if (null == out) {
        throw new NullPointerException("out must not be null");
    }
    byte[] buf = new byte[1024 * 8];
    int read = -1;
    while ((read = in.read(buf)) > -1) {
        out.write(buf, 0, read);
    }
}

/**
 * Copies in's contents to out, and ensures that in is closed afterwards.
 * 
 * @param in
 *            Must not be null.
 * @param out
 *            Must not be null.
 * 
 * @throws IOException
 */
void copyStreamAndCloseIn(InputStream in, OutputStream out) throws IOException {
    try {
        copyStream(in, out);
    } finally {
        in.close();
    }
}

public void service(HttpServletRequest request, HttpServletResponse response) throws IOException {
    String filepath = getServletContext().getRealPath("\\") + "temp";
    String filename = "csv" + dateFormat.format(date) + ".csv";
    File file = new File(filepath + filename);
    file.createNewFile();

    saveList(file, list);

    long length = file.length();
    response.setContentType("text/csv");
    response.addHeader("Content-Disposition", "attachment; filename=" + filename);
    response.setContentLength((int) length);

    copyStreamAndCloseIn(new FileInputStream(file), response.getOutputStream());
}

As for the strange output et-ts12et-ts12et-ts12ÿ, I’m not sure why that would be.

How are you viewing this value? Printing to the console, reading the file afterwards? Both printing to the console and opening the file in another editor could produce strange results depending on the character encoding in use.