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    <p>Are you doing this for logging purposes? If so there are <a href="http://en.wikipedia.org/wiki/Java_logging_framework" rel="noreferrer">several libraries for this</a>. Two of the most popular are <a href="http://logging.apache.org/log4j/" rel="noreferrer">Log4j</a> and <a href="http://logback.qos.ch/" rel="noreferrer">Logback</a>.</p> <h2>Java 7+</h2> <p>If you just need to do this one time, the <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html" rel="noreferrer">Files class</a> makes this easy:</p> <pre><code>try { Files.write(Paths.get("myfile.txt"), "the text".getBytes(), StandardOpenOption.APPEND); }catch (IOException e) { //exception handling left as an exercise for the reader } </code></pre> <p><sup><strong>Careful</strong>: The above approach will throw a <code>NoSuchFileException</code> if the file does not already exist. It also does not append a newline automatically (which you often want when appending to a text file). <a href="https://stackoverflow.com/a/44301865/18511">Steve Chambers's answer</a> covers how you could do this with <code>Files</code> class.</sup></p> <p>However, if you will be writing to the same file many times, the above has to open and close the file on the disk many times, which is a slow operation. In this case, a buffered writer is better:</p> <pre><code>try(FileWriter fw = new FileWriter("myfile.txt", true); BufferedWriter bw = new BufferedWriter(fw); PrintWriter out = new PrintWriter(bw)) { out.println("the text"); //more code out.println("more text"); //more code } catch (IOException e) { //exception handling left as an exercise for the reader } </code></pre> <p><strong>Notes:</strong></p> <ul> <li>The second parameter to the <code>FileWriter</code> constructor will tell it to append to the file, rather than writing a new file. (If the file does not exist, it will be created.)</li> <li>Using a <code>BufferedWriter</code> is recommended for an expensive writer (such as <code>FileWriter</code>).</li> <li>Using a <code>PrintWriter</code> gives you access to <code>println</code> syntax that you're probably used to from <code>System.out</code>.</li> <li>But the <code>BufferedWriter</code> and <code>PrintWriter</code> wrappers are not strictly necessary.</li> </ul> <hr> <h2>Older Java</h2> <pre><code>try { PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("myfile.txt", true))); out.println("the text"); out.close(); } catch (IOException e) { //exception handling left as an exercise for the reader } </code></pre> <hr> <h2>Exception Handling</h2> <p>If you need robust exception handling for older Java, it gets very verbose:</p> <pre><code>FileWriter fw = null; BufferedWriter bw = null; PrintWriter out = null; try { fw = new FileWriter("myfile.txt", true); bw = new BufferedWriter(fw); out = new PrintWriter(bw); out.println("the text"); out.close(); } catch (IOException e) { //exception handling left as an exercise for the reader } finally { try { if(out != null) out.close(); } catch (IOException e) { //exception handling left as an exercise for the reader } try { if(bw != null) bw.close(); } catch (IOException e) { //exception handling left as an exercise for the reader } try { if(fw != null) fw.close(); } catch (IOException e) { //exception handling left as an exercise for the reader } } </code></pre>
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