Java InputStreamReader Create readTextFile(String filename, int maxNumLines, boolean startAtBeginning)

Description

Read in the last few lines of a (newline delimited) textfile, or null if the file doesn't exist.

License

Open Source License

Parameter

Parameter	Description
startAtBeginning	if true, read the first maxNumLines, otherwise read the last maxNumLines
maxNumLines	max number of lines (or -1 for unlimited)

Return

string or null; does not throw IOException.

Declaration

public static String readTextFile(String filename, int maxNumLines, boolean startAtBeginning) 

Method Source Code

//package com.java2s;
//License from project: Open Source License 

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStreamReader;

import java.util.ArrayList;

import java.util.List;

public class Main {
    /**/*from   w  w w.j ava  2 s .c  o  m*/
     * Read in the last few lines of a (newline delimited) textfile, or null if
     * the file doesn't exist.  
     *
     * Warning - this inefficiently allocates a StringBuilder of size maxNumLines*80,
     *           so don't make it too big.
     * Warning - converts \r\n to \n
     *
     * @param startAtBeginning if true, read the first maxNumLines, otherwise read
     *                         the last maxNumLines
     * @param maxNumLines max number of lines (or -1 for unlimited)
     * @return string or null; does not throw IOException.
     *
     */
    public static String readTextFile(String filename, int maxNumLines, boolean startAtBeginning) {
        File f = new File(filename);
        if (!f.exists())
            return null;
        FileInputStream fis = null;
        BufferedReader in = null;
        try {
            fis = new FileInputStream(f);
            in = new BufferedReader(new InputStreamReader(fis, "UTF-8"));
            List<String> lines = new ArrayList<String>(maxNumLines > 0 ? maxNumLines : 64);
            String line = null;
            while ((line = in.readLine()) != null) {
                lines.add(line);
                if ((maxNumLines > 0) && (lines.size() >= maxNumLines)) {
                    if (startAtBeginning)
                        break;
                    else
                        lines.remove(0);
                }
            }
            StringBuilder buf = new StringBuilder(lines.size() * 80);
            for (int i = 0; i < lines.size(); i++) {
                buf.append(lines.get(i)).append('\n');
            }
            return buf.toString();
        } catch (IOException ioe) {
            return null;
        } finally {
            if (in != null)
                try {
                    in.close();
                } catch (IOException ioe) {
                }
        }
    }
}

Related

1. readTextFile(final File file)
2. ReadTextFile(InputStream is)
3. readTextFile(java.io.File file)
4. readTextFile(Reader reader)
5. readTextFile(String fileName)
6. readTextFile(String filePath, String charset)
7. readTextFile(String fullPathFilename)
8. readTextFile(String realPath)
9. readTextFileAsStringArray(final File file, final String charSet)