Related
I need to append text repeatedly to an existing file in Java. How do I do that?
Are you doing this for logging purposes? If so there are several libraries for this. Two of the most popular are Log4j and Logback.
Java 7+
For a one-time task, the Files class makes this easy:
try {
Files.write(Paths.get("myfile.txt"), "the text".getBytes(), StandardOpenOption.APPEND);
}catch (IOException e) {
//exception handling left as an exercise for the reader
}
Careful: The above approach will throw a NoSuchFileException 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). Another approach is to pass both CREATE and APPEND options, which will create the file first if it doesn't already exist:
private void write(final String s) throws IOException {
Files.writeString(
Path.of(System.getProperty("java.io.tmpdir"), "filename.txt"),
s + System.lineSeparator(),
CREATE, APPEND
);
}
However, if you will be writing to the same file many times, the above snippets must open and close the file on the disk many times, which is a slow operation. In this case, a BufferedWriter is faster:
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
}
Notes:
The second parameter to the FileWriter 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.)
Using a BufferedWriter is recommended for an expensive writer (such as FileWriter).
Using a PrintWriter gives you access to println syntax that you're probably used to from System.out.
But the BufferedWriter and PrintWriter wrappers are not strictly necessary.
Older Java
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
}
Exception Handling
If you need robust exception handling for older Java, it gets very verbose:
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
}
}
You can use fileWriter with a flag set to true , for appending.
try
{
String filename= "MyFile.txt";
FileWriter fw = new FileWriter(filename,true); //the true will append the new data
fw.write("add a line\n");//appends the string to the file
fw.close();
}
catch(IOException ioe)
{
System.err.println("IOException: " + ioe.getMessage());
}
Shouldn't all of the answers here with try/catch blocks have the .close() pieces contained in a finally block?
Example for marked answer:
PrintWriter out = null;
try {
out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)));
out.println("the text");
} catch (IOException e) {
System.err.println(e);
} finally {
if (out != null) {
out.close();
}
}
Also, as of Java 7, you can use a try-with-resources statement. No finally block is required for closing the declared resource(s) because it is handled automatically, and is also less verbose:
try(PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)))) {
out.println("the text");
} catch (IOException e) {
System.err.println(e);
}
Using Apache Commons 2.1:
import org.apache.logging.log4j.core.util.FileUtils;
FileUtils.writeStringToFile(file, "String to append", true);
Slightly expanding on Kip's answer,
here is a simple Java 7+ method to append a new line to a file, creating it if it doesn't already exist:
try {
final Path path = Paths.get("path/to/filename.txt");
Files.write(path, Arrays.asList("New line to append"), StandardCharsets.UTF_8,
Files.exists(path) ? StandardOpenOption.APPEND : StandardOpenOption.CREATE);
} catch (final IOException ioe) {
// Add your own exception handling...
}
Further notes:
The above uses the Files.write overload that writes lines of text to a file (i.e. similar to a println command). To just write text to the end (i.e. similar to a print command), an alternative Files.write overload can be used, passing in a byte array (e.g. "mytext".getBytes(StandardCharsets.UTF_8)).
The CREATE option will only work if the specified directory already exists - if it doesn't, a NoSuchFileException is thrown. If required, the following code could be added after setting path to create the directory structure:
Path pathParent = path.getParent();
if (!Files.exists(pathParent)) {
Files.createDirectories(pathParent);
}
Make sure the stream gets properly closed in all scenarios.
It's a bit alarming how many of these answers leave the file handle open in case of an error. The answer https://stackoverflow.com/a/15053443/2498188 is on the money but only because BufferedWriter() cannot throw. If it could then an exception would leave the FileWriter object open.
A more general way of doing this that doesn't care if BufferedWriter() can throw:
PrintWriter out = null;
BufferedWriter bw = null;
FileWriter fw = null;
try{
fw = new FileWriter("outfilename", true);
bw = new BufferedWriter(fw);
out = new PrintWriter(bw);
out.println("the text");
}
catch( IOException e ){
// File writing/opening failed at some stage.
}
finally{
try{
if( out != null ){
out.close(); // Will close bw and fw too
}
else if( bw != null ){
bw.close(); // Will close fw too
}
else if( fw != null ){
fw.close();
}
else{
// Oh boy did it fail hard! :3
}
}
catch( IOException e ){
// Closing the file writers failed for some obscure reason
}
}
Edit:
As of Java 7, the recommended way is to use "try with resources" and let the JVM deal with it:
try( FileWriter fw = new FileWriter("outfilename", true);
BufferedWriter bw = new BufferedWriter(fw);
PrintWriter out = new PrintWriter(bw)){
out.println("the text");
}
catch( IOException e ){
// File writing/opening failed at some stage.
}
In Java-7 it also can be done such kind:
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
//---------------------
Path filePath = Paths.get("someFile.txt");
if (!Files.exists(filePath)) {
Files.createFile(filePath);
}
Files.write(filePath, "Text to be added".getBytes(), StandardOpenOption.APPEND);
java 7+
In my humble opinion since I am fan of plain java, I would suggest something that it is a combination of the aforementioned answers. Maybe I am late for the party. Here is the code:
String sampleText = "test" + System.getProperty("line.separator");
Files.write(Paths.get(filePath), sampleText.getBytes(StandardCharsets.UTF_8),
StandardOpenOption.CREATE, StandardOpenOption.APPEND);
If the file doesn't exist, it creates it and if already exists it appends the
sampleText to the existing file. Using this, saves you from adding unnecessary libs to your classpath.
This can be done in one line of code. Hope this helps :)
Files.write(Paths.get(fileName), msg.getBytes(), StandardOpenOption.APPEND);
I just add small detail:
new FileWriter("outfilename", true)
2.nd parameter (true) is a feature (or, interface) called appendable (http://docs.oracle.com/javase/7/docs/api/java/lang/Appendable.html). It is responsible for being able to add some content to the end of particular file/stream. This interface is implemented since Java 1.5. Each object (i.e. BufferedWriter, CharArrayWriter, CharBuffer, FileWriter, FilterWriter, LogStream, OutputStreamWriter, PipedWriter, PrintStream, PrintWriter, StringBuffer, StringBuilder, StringWriter, Writer) with this interface can be used for adding content
In other words, you can add some content to your gzipped file, or some http process
Using java.nio.Files along with java.nio.file.StandardOpenOption
PrintWriter out = null;
BufferedWriter bufWriter;
try{
bufWriter =
Files.newBufferedWriter(
Paths.get("log.txt"),
Charset.forName("UTF8"),
StandardOpenOption.WRITE,
StandardOpenOption.APPEND,
StandardOpenOption.CREATE);
out = new PrintWriter(bufWriter, true);
}catch(IOException e){
//Oh, no! Failed to create PrintWriter
}
//After successful creation of PrintWriter
out.println("Text to be appended");
//After done writing, remember to close!
out.close();
This creates a BufferedWriter using Files, which accepts StandardOpenOption parameters, and an auto-flushing PrintWriter from the resultant BufferedWriter. PrintWriter's println() method, can then be called to write to the file.
The StandardOpenOption parameters used in this code: opens the file for writing, only appends to the file, and creates the file if it does not exist.
Paths.get("path here") can be replaced with new File("path here").toPath().
And Charset.forName("charset name") can be modified to accommodate the desired Charset.
Sample, using Guava:
File to = new File("C:/test/test.csv");
for (int i = 0; i < 42; i++) {
CharSequence from = "some string" + i + "\n";
Files.append(from, to, Charsets.UTF_8);
}
FileOutputStream fos = new FileOutputStream("File_Name", true);
fos.write(data);
the true allows to append the data in the existing file. If we will write
FileOutputStream fos = new FileOutputStream("File_Name");
It will overwrite the existing file. So go for first approach.
Try with bufferFileWriter.append, it works with me.
FileWriter fileWriter;
try {
fileWriter = new FileWriter(file,true);
BufferedWriter bufferFileWriter = new BufferedWriter(fileWriter);
bufferFileWriter.append(obj.toJSONString());
bufferFileWriter.newLine();
bufferFileWriter.close();
} catch (IOException ex) {
Logger.getLogger(JsonTest.class.getName()).log(Level.SEVERE, null, ex);
}
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
public class Writer {
public static void main(String args[]){
doWrite("output.txt","Content to be appended to file");
}
public static void doWrite(String filePath,String contentToBeAppended){
try(
FileWriter fw = new FileWriter(filePath, true);
BufferedWriter bw = new BufferedWriter(fw);
PrintWriter out = new PrintWriter(bw)
)
{
out.println(contentToBeAppended);
}
catch( IOException e ){
// File writing/opening failed at some stage.
}
}
}
String str;
String path = "C:/Users/...the path..../iin.txt"; // you can input also..i created this way :P
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
PrintWriter pw = new PrintWriter(new FileWriter(path, true));
try
{
while(true)
{
System.out.println("Enter the text : ");
str = br.readLine();
if(str.equalsIgnoreCase("exit"))
break;
else
pw.println(str);
}
}
catch (Exception e)
{
//oh noes!
}
finally
{
pw.close();
}
this will do what you intend for..
You can also try this :
JFileChooser c= new JFileChooser();
c.showOpenDialog(c);
File write_file = c.getSelectedFile();
String Content = "Writing into file"; //what u would like to append to the file
try
{
RandomAccessFile raf = new RandomAccessFile(write_file, "rw");
long length = raf.length();
//System.out.println(length);
raf.setLength(length + 1); //+ (integer value) for spacing
raf.seek(raf.length());
raf.writeBytes(Content);
raf.close();
}
catch (Exception e) {
//any exception handling method of ur choice
}
Better to use try-with-resources then all that pre-java 7 finally business
static void appendStringToFile(Path file, String s) throws IOException {
try (BufferedWriter out = Files.newBufferedWriter(file, StandardCharsets.UTF_8, StandardOpenOption.APPEND)) {
out.append(s);
out.newLine();
}
}
If we are using Java 7 and above and also know the content to be added (appended) to the file we can make use of newBufferedWriter method in NIO package.
public static void main(String[] args) {
Path FILE_PATH = Paths.get("C:/temp", "temp.txt");
String text = "\n Welcome to Java 8";
//Writing to the file temp.txt
try (BufferedWriter writer = Files.newBufferedWriter(FILE_PATH, StandardCharsets.UTF_8, StandardOpenOption.APPEND)) {
writer.write(text);
} catch (IOException e) {
e.printStackTrace();
}
}
There are few points to note:
It is always a good habit to specify charset encoding and for that we have constant in class StandardCharsets.
The code uses try-with-resource statement in which resources are automatically closed after the try.
Though OP has not asked but just in case we want to search for lines having some specific keyword e.g. confidential we can make use of stream APIs in Java:
//Reading from the file the first line which contains word "confidential"
try {
Stream<String> lines = Files.lines(FILE_PATH);
Optional<String> containsJava = lines.filter(l->l.contains("confidential")).findFirst();
if(containsJava.isPresent()){
System.out.println(containsJava.get());
}
} catch (IOException e) {
e.printStackTrace();
}
FileOutputStream stream = new FileOutputStream(path, true);
try {
stream.write(
string.getBytes("UTF-8") // Choose your encoding.
);
} finally {
stream.close();
}
Then catch an IOException somewhere upstream.
Create a function anywhere in your project and simply call that function where ever you need it.
Guys you got to remember that you guys are calling active threads that you are not calling asynchronously and since it would likely be a good 5 to 10 pages to get it done right.
Why not spend more time on your project and forget about writing anything already written.
Properly
//Adding a static modifier would make this accessible anywhere in your app
public Logger getLogger()
{
return java.util.logging.Logger.getLogger("MyLogFileName");
}
//call the method anywhere and append what you want to log
//Logger class will take care of putting timestamps for you
//plus the are ansychronously done so more of the
//processing power will go into your application
//from inside a function body in the same class ...{...
getLogger().log(Level.INFO,"the text you want to append");
...}...
/*********log file resides in server root log files********/
three lines of code two really since the third actually appends text. :P
Library
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
Code
public void append()
{
try
{
String path = "D:/sample.txt";
File file = new File(path);
FileWriter fileWriter = new FileWriter(file,true);
BufferedWriter bufferFileWriter = new BufferedWriter(fileWriter);
fileWriter.append("Sample text in the file to append");
bufferFileWriter.close();
System.out.println("User Registration Completed");
}catch(Exception ex)
{
System.out.println(ex);
}
}
I might suggest the apache commons project. This project already provides a framework for doing what you need (i.e. flexible filtering of collections).
The following method let's you append text to some file:
private void appendToFile(String filePath, String text)
{
PrintWriter fileWriter = null;
try
{
fileWriter = new PrintWriter(new BufferedWriter(new FileWriter(
filePath, true)));
fileWriter.println(text);
} catch (IOException ioException)
{
ioException.printStackTrace();
} finally
{
if (fileWriter != null)
{
fileWriter.close();
}
}
}
Alternatively using FileUtils:
public static void appendToFile(String filePath, String text) throws IOException
{
File file = new File(filePath);
if(!file.exists())
{
file.createNewFile();
}
String fileContents = FileUtils.readFileToString(file);
if(file.length() != 0)
{
fileContents = fileContents.concat(System.lineSeparator());
}
fileContents = fileContents.concat(text);
FileUtils.writeStringToFile(file, fileContents);
}
It is not efficient but works fine. Line breaks are handled correctly and a new file is created if one didn't exist yet.
This code will fulifil your need:
FileWriter fw=new FileWriter("C:\\file.json",true);
fw.write("ssssss");
fw.close();
In case you want to ADD SOME TEXT IN SPECIFIC LINES you can first read the whole file, append the text wherever you want and then overwrite everything like in the code below:
public static void addDatatoFile(String data1, String data2){
String fullPath = "/home/user/dir/file.csv";
File dir = new File(fullPath);
List<String> l = new LinkedList<String>();
try (BufferedReader br = new BufferedReader(new FileReader(dir))) {
String line;
int count = 0;
while ((line = br.readLine()) != null) {
if(count == 1){
//add data at the end of second line
line += data1;
}else if(count == 2){
//add other data at the end of third line
line += data2;
}
l.add(line);
count++;
}
br.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
createFileFromList(l, dir);
}
public static void createFileFromList(List<String> list, File f){
PrintWriter writer;
try {
writer = new PrintWriter(f, "UTF-8");
for (String d : list) {
writer.println(d.toString());
}
writer.close();
} catch (FileNotFoundException | UnsupportedEncodingException e) {
e.printStackTrace();
}
}
My answer:
JFileChooser chooser= new JFileChooser();
chooser.showOpenDialog(chooser);
File file = chooser.getSelectedFile();
String Content = "What you want to append to file";
try
{
RandomAccessFile random = new RandomAccessFile(file, "rw");
long length = random.length();
random.setLength(length + 1);
random.seek(random.length());
random.writeBytes(Content);
random.close();
}
catch (Exception exception) {
//exception handling
}
/**********************************************************************
* it will write content to a specified file
*
* #param keyString
* #throws IOException
*********************************************************************/
public static void writeToFile(String keyString,String textFilePAth) throws IOException {
// For output to file
File a = new File(textFilePAth);
if (!a.exists()) {
a.createNewFile();
}
FileWriter fw = new FileWriter(a.getAbsoluteFile(), true);
BufferedWriter bw = new BufferedWriter(fw);
bw.append(keyString);
bw.newLine();
bw.close();
}// end of writeToFile()
For JDK version >= 7
You can utilise this simple method which appends the given content to the specified file:
void appendToFile(String filePath, String content) {
try (FileWriter fw = new FileWriter(filePath, true)) {
fw.write(content + System.lineSeparator());
} catch (IOException e) {
// TODO handle exception
}
}
We are constructing a FileWriter object in append mode.
You can use the follong code to append the content in the file:
String fileName="/home/shriram/Desktop/Images/"+"test.txt";
FileWriter fw=new FileWriter(fileName,true);
fw.write("here will be you content to insert or append in file");
fw.close();
FileWriter fw1=new FileWriter(fileName,true);
fw1.write("another content will be here to be append in the same file");
fw1.close();
I need to append text repeatedly to an existing file in Java. How do I do that?
Are you doing this for logging purposes? If so there are several libraries for this. Two of the most popular are Log4j and Logback.
Java 7+
For a one-time task, the Files class makes this easy:
try {
Files.write(Paths.get("myfile.txt"), "the text".getBytes(), StandardOpenOption.APPEND);
}catch (IOException e) {
//exception handling left as an exercise for the reader
}
Careful: The above approach will throw a NoSuchFileException 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). Another approach is to pass both CREATE and APPEND options, which will create the file first if it doesn't already exist:
private void write(final String s) throws IOException {
Files.writeString(
Path.of(System.getProperty("java.io.tmpdir"), "filename.txt"),
s + System.lineSeparator(),
CREATE, APPEND
);
}
However, if you will be writing to the same file many times, the above snippets must open and close the file on the disk many times, which is a slow operation. In this case, a BufferedWriter is faster:
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
}
Notes:
The second parameter to the FileWriter 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.)
Using a BufferedWriter is recommended for an expensive writer (such as FileWriter).
Using a PrintWriter gives you access to println syntax that you're probably used to from System.out.
But the BufferedWriter and PrintWriter wrappers are not strictly necessary.
Older Java
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
}
Exception Handling
If you need robust exception handling for older Java, it gets very verbose:
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
}
}
You can use fileWriter with a flag set to true , for appending.
try
{
String filename= "MyFile.txt";
FileWriter fw = new FileWriter(filename,true); //the true will append the new data
fw.write("add a line\n");//appends the string to the file
fw.close();
}
catch(IOException ioe)
{
System.err.println("IOException: " + ioe.getMessage());
}
Shouldn't all of the answers here with try/catch blocks have the .close() pieces contained in a finally block?
Example for marked answer:
PrintWriter out = null;
try {
out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)));
out.println("the text");
} catch (IOException e) {
System.err.println(e);
} finally {
if (out != null) {
out.close();
}
}
Also, as of Java 7, you can use a try-with-resources statement. No finally block is required for closing the declared resource(s) because it is handled automatically, and is also less verbose:
try(PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)))) {
out.println("the text");
} catch (IOException e) {
System.err.println(e);
}
Using Apache Commons 2.1:
import org.apache.logging.log4j.core.util.FileUtils;
FileUtils.writeStringToFile(file, "String to append", true);
Slightly expanding on Kip's answer,
here is a simple Java 7+ method to append a new line to a file, creating it if it doesn't already exist:
try {
final Path path = Paths.get("path/to/filename.txt");
Files.write(path, Arrays.asList("New line to append"), StandardCharsets.UTF_8,
Files.exists(path) ? StandardOpenOption.APPEND : StandardOpenOption.CREATE);
} catch (final IOException ioe) {
// Add your own exception handling...
}
Further notes:
The above uses the Files.write overload that writes lines of text to a file (i.e. similar to a println command). To just write text to the end (i.e. similar to a print command), an alternative Files.write overload can be used, passing in a byte array (e.g. "mytext".getBytes(StandardCharsets.UTF_8)).
The CREATE option will only work if the specified directory already exists - if it doesn't, a NoSuchFileException is thrown. If required, the following code could be added after setting path to create the directory structure:
Path pathParent = path.getParent();
if (!Files.exists(pathParent)) {
Files.createDirectories(pathParent);
}
Make sure the stream gets properly closed in all scenarios.
It's a bit alarming how many of these answers leave the file handle open in case of an error. The answer https://stackoverflow.com/a/15053443/2498188 is on the money but only because BufferedWriter() cannot throw. If it could then an exception would leave the FileWriter object open.
A more general way of doing this that doesn't care if BufferedWriter() can throw:
PrintWriter out = null;
BufferedWriter bw = null;
FileWriter fw = null;
try{
fw = new FileWriter("outfilename", true);
bw = new BufferedWriter(fw);
out = new PrintWriter(bw);
out.println("the text");
}
catch( IOException e ){
// File writing/opening failed at some stage.
}
finally{
try{
if( out != null ){
out.close(); // Will close bw and fw too
}
else if( bw != null ){
bw.close(); // Will close fw too
}
else if( fw != null ){
fw.close();
}
else{
// Oh boy did it fail hard! :3
}
}
catch( IOException e ){
// Closing the file writers failed for some obscure reason
}
}
Edit:
As of Java 7, the recommended way is to use "try with resources" and let the JVM deal with it:
try( FileWriter fw = new FileWriter("outfilename", true);
BufferedWriter bw = new BufferedWriter(fw);
PrintWriter out = new PrintWriter(bw)){
out.println("the text");
}
catch( IOException e ){
// File writing/opening failed at some stage.
}
In Java-7 it also can be done such kind:
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
//---------------------
Path filePath = Paths.get("someFile.txt");
if (!Files.exists(filePath)) {
Files.createFile(filePath);
}
Files.write(filePath, "Text to be added".getBytes(), StandardOpenOption.APPEND);
java 7+
In my humble opinion since I am fan of plain java, I would suggest something that it is a combination of the aforementioned answers. Maybe I am late for the party. Here is the code:
String sampleText = "test" + System.getProperty("line.separator");
Files.write(Paths.get(filePath), sampleText.getBytes(StandardCharsets.UTF_8),
StandardOpenOption.CREATE, StandardOpenOption.APPEND);
If the file doesn't exist, it creates it and if already exists it appends the
sampleText to the existing file. Using this, saves you from adding unnecessary libs to your classpath.
This can be done in one line of code. Hope this helps :)
Files.write(Paths.get(fileName), msg.getBytes(), StandardOpenOption.APPEND);
I just add small detail:
new FileWriter("outfilename", true)
2.nd parameter (true) is a feature (or, interface) called appendable (http://docs.oracle.com/javase/7/docs/api/java/lang/Appendable.html). It is responsible for being able to add some content to the end of particular file/stream. This interface is implemented since Java 1.5. Each object (i.e. BufferedWriter, CharArrayWriter, CharBuffer, FileWriter, FilterWriter, LogStream, OutputStreamWriter, PipedWriter, PrintStream, PrintWriter, StringBuffer, StringBuilder, StringWriter, Writer) with this interface can be used for adding content
In other words, you can add some content to your gzipped file, or some http process
Using java.nio.Files along with java.nio.file.StandardOpenOption
PrintWriter out = null;
BufferedWriter bufWriter;
try{
bufWriter =
Files.newBufferedWriter(
Paths.get("log.txt"),
Charset.forName("UTF8"),
StandardOpenOption.WRITE,
StandardOpenOption.APPEND,
StandardOpenOption.CREATE);
out = new PrintWriter(bufWriter, true);
}catch(IOException e){
//Oh, no! Failed to create PrintWriter
}
//After successful creation of PrintWriter
out.println("Text to be appended");
//After done writing, remember to close!
out.close();
This creates a BufferedWriter using Files, which accepts StandardOpenOption parameters, and an auto-flushing PrintWriter from the resultant BufferedWriter. PrintWriter's println() method, can then be called to write to the file.
The StandardOpenOption parameters used in this code: opens the file for writing, only appends to the file, and creates the file if it does not exist.
Paths.get("path here") can be replaced with new File("path here").toPath().
And Charset.forName("charset name") can be modified to accommodate the desired Charset.
Sample, using Guava:
File to = new File("C:/test/test.csv");
for (int i = 0; i < 42; i++) {
CharSequence from = "some string" + i + "\n";
Files.append(from, to, Charsets.UTF_8);
}
FileOutputStream fos = new FileOutputStream("File_Name", true);
fos.write(data);
the true allows to append the data in the existing file. If we will write
FileOutputStream fos = new FileOutputStream("File_Name");
It will overwrite the existing file. So go for first approach.
Try with bufferFileWriter.append, it works with me.
FileWriter fileWriter;
try {
fileWriter = new FileWriter(file,true);
BufferedWriter bufferFileWriter = new BufferedWriter(fileWriter);
bufferFileWriter.append(obj.toJSONString());
bufferFileWriter.newLine();
bufferFileWriter.close();
} catch (IOException ex) {
Logger.getLogger(JsonTest.class.getName()).log(Level.SEVERE, null, ex);
}
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
public class Writer {
public static void main(String args[]){
doWrite("output.txt","Content to be appended to file");
}
public static void doWrite(String filePath,String contentToBeAppended){
try(
FileWriter fw = new FileWriter(filePath, true);
BufferedWriter bw = new BufferedWriter(fw);
PrintWriter out = new PrintWriter(bw)
)
{
out.println(contentToBeAppended);
}
catch( IOException e ){
// File writing/opening failed at some stage.
}
}
}
String str;
String path = "C:/Users/...the path..../iin.txt"; // you can input also..i created this way :P
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
PrintWriter pw = new PrintWriter(new FileWriter(path, true));
try
{
while(true)
{
System.out.println("Enter the text : ");
str = br.readLine();
if(str.equalsIgnoreCase("exit"))
break;
else
pw.println(str);
}
}
catch (Exception e)
{
//oh noes!
}
finally
{
pw.close();
}
this will do what you intend for..
You can also try this :
JFileChooser c= new JFileChooser();
c.showOpenDialog(c);
File write_file = c.getSelectedFile();
String Content = "Writing into file"; //what u would like to append to the file
try
{
RandomAccessFile raf = new RandomAccessFile(write_file, "rw");
long length = raf.length();
//System.out.println(length);
raf.setLength(length + 1); //+ (integer value) for spacing
raf.seek(raf.length());
raf.writeBytes(Content);
raf.close();
}
catch (Exception e) {
//any exception handling method of ur choice
}
Better to use try-with-resources then all that pre-java 7 finally business
static void appendStringToFile(Path file, String s) throws IOException {
try (BufferedWriter out = Files.newBufferedWriter(file, StandardCharsets.UTF_8, StandardOpenOption.APPEND)) {
out.append(s);
out.newLine();
}
}
If we are using Java 7 and above and also know the content to be added (appended) to the file we can make use of newBufferedWriter method in NIO package.
public static void main(String[] args) {
Path FILE_PATH = Paths.get("C:/temp", "temp.txt");
String text = "\n Welcome to Java 8";
//Writing to the file temp.txt
try (BufferedWriter writer = Files.newBufferedWriter(FILE_PATH, StandardCharsets.UTF_8, StandardOpenOption.APPEND)) {
writer.write(text);
} catch (IOException e) {
e.printStackTrace();
}
}
There are few points to note:
It is always a good habit to specify charset encoding and for that we have constant in class StandardCharsets.
The code uses try-with-resource statement in which resources are automatically closed after the try.
Though OP has not asked but just in case we want to search for lines having some specific keyword e.g. confidential we can make use of stream APIs in Java:
//Reading from the file the first line which contains word "confidential"
try {
Stream<String> lines = Files.lines(FILE_PATH);
Optional<String> containsJava = lines.filter(l->l.contains("confidential")).findFirst();
if(containsJava.isPresent()){
System.out.println(containsJava.get());
}
} catch (IOException e) {
e.printStackTrace();
}
FileOutputStream stream = new FileOutputStream(path, true);
try {
stream.write(
string.getBytes("UTF-8") // Choose your encoding.
);
} finally {
stream.close();
}
Then catch an IOException somewhere upstream.
Create a function anywhere in your project and simply call that function where ever you need it.
Guys you got to remember that you guys are calling active threads that you are not calling asynchronously and since it would likely be a good 5 to 10 pages to get it done right.
Why not spend more time on your project and forget about writing anything already written.
Properly
//Adding a static modifier would make this accessible anywhere in your app
public Logger getLogger()
{
return java.util.logging.Logger.getLogger("MyLogFileName");
}
//call the method anywhere and append what you want to log
//Logger class will take care of putting timestamps for you
//plus the are ansychronously done so more of the
//processing power will go into your application
//from inside a function body in the same class ...{...
getLogger().log(Level.INFO,"the text you want to append");
...}...
/*********log file resides in server root log files********/
three lines of code two really since the third actually appends text. :P
Library
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
Code
public void append()
{
try
{
String path = "D:/sample.txt";
File file = new File(path);
FileWriter fileWriter = new FileWriter(file,true);
BufferedWriter bufferFileWriter = new BufferedWriter(fileWriter);
fileWriter.append("Sample text in the file to append");
bufferFileWriter.close();
System.out.println("User Registration Completed");
}catch(Exception ex)
{
System.out.println(ex);
}
}
I might suggest the apache commons project. This project already provides a framework for doing what you need (i.e. flexible filtering of collections).
The following method let's you append text to some file:
private void appendToFile(String filePath, String text)
{
PrintWriter fileWriter = null;
try
{
fileWriter = new PrintWriter(new BufferedWriter(new FileWriter(
filePath, true)));
fileWriter.println(text);
} catch (IOException ioException)
{
ioException.printStackTrace();
} finally
{
if (fileWriter != null)
{
fileWriter.close();
}
}
}
Alternatively using FileUtils:
public static void appendToFile(String filePath, String text) throws IOException
{
File file = new File(filePath);
if(!file.exists())
{
file.createNewFile();
}
String fileContents = FileUtils.readFileToString(file);
if(file.length() != 0)
{
fileContents = fileContents.concat(System.lineSeparator());
}
fileContents = fileContents.concat(text);
FileUtils.writeStringToFile(file, fileContents);
}
It is not efficient but works fine. Line breaks are handled correctly and a new file is created if one didn't exist yet.
This code will fulifil your need:
FileWriter fw=new FileWriter("C:\\file.json",true);
fw.write("ssssss");
fw.close();
In case you want to ADD SOME TEXT IN SPECIFIC LINES you can first read the whole file, append the text wherever you want and then overwrite everything like in the code below:
public static void addDatatoFile(String data1, String data2){
String fullPath = "/home/user/dir/file.csv";
File dir = new File(fullPath);
List<String> l = new LinkedList<String>();
try (BufferedReader br = new BufferedReader(new FileReader(dir))) {
String line;
int count = 0;
while ((line = br.readLine()) != null) {
if(count == 1){
//add data at the end of second line
line += data1;
}else if(count == 2){
//add other data at the end of third line
line += data2;
}
l.add(line);
count++;
}
br.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
createFileFromList(l, dir);
}
public static void createFileFromList(List<String> list, File f){
PrintWriter writer;
try {
writer = new PrintWriter(f, "UTF-8");
for (String d : list) {
writer.println(d.toString());
}
writer.close();
} catch (FileNotFoundException | UnsupportedEncodingException e) {
e.printStackTrace();
}
}
My answer:
JFileChooser chooser= new JFileChooser();
chooser.showOpenDialog(chooser);
File file = chooser.getSelectedFile();
String Content = "What you want to append to file";
try
{
RandomAccessFile random = new RandomAccessFile(file, "rw");
long length = random.length();
random.setLength(length + 1);
random.seek(random.length());
random.writeBytes(Content);
random.close();
}
catch (Exception exception) {
//exception handling
}
/**********************************************************************
* it will write content to a specified file
*
* #param keyString
* #throws IOException
*********************************************************************/
public static void writeToFile(String keyString,String textFilePAth) throws IOException {
// For output to file
File a = new File(textFilePAth);
if (!a.exists()) {
a.createNewFile();
}
FileWriter fw = new FileWriter(a.getAbsoluteFile(), true);
BufferedWriter bw = new BufferedWriter(fw);
bw.append(keyString);
bw.newLine();
bw.close();
}// end of writeToFile()
For JDK version >= 7
You can utilise this simple method which appends the given content to the specified file:
void appendToFile(String filePath, String content) {
try (FileWriter fw = new FileWriter(filePath, true)) {
fw.write(content + System.lineSeparator());
} catch (IOException e) {
// TODO handle exception
}
}
We are constructing a FileWriter object in append mode.
You can use the follong code to append the content in the file:
String fileName="/home/shriram/Desktop/Images/"+"test.txt";
FileWriter fw=new FileWriter(fileName,true);
fw.write("here will be you content to insert or append in file");
fw.close();
FileWriter fw1=new FileWriter(fileName,true);
fw1.write("another content will be here to be append in the same file");
fw1.close();
I am trying to rewrite in a file, alongside with the other text in it(not overwrite). But i don't know how can i do it using the exception as my buffered reader lose his initialization.
BufferedReader br;
try {
br = new BufferedReader(new FileReader("file.txt"));
String line ;
while((line = br.readLine()) != null){
System.out.println(line);
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
BufferedWriter bw;
try {
File file = new File("file.txt");
bw = new BufferedWriter(new FileWriter("file.txt"));
if(br.readLine() != null) //ERROR Local variable may have not been initialized
bw.newLine();
bw.write("Hello");
bw.flush();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
FileWriter has the ability to set the append flag new FileWriter(file, append)
or if you want to use your version
Initialize the variable with null
BufferedReader br = null;
try with resource may be useful here as well, because it closes everything for you automatically.
Simple. Initialize the variable to null.
Say first line as,
BufferedReader br = null;
...
try {
File file = new File("file.txt");
bw = new BufferedWriter(new FileWriter("file.txt",true));
if(br.readLine() != null) //ERROR Local variable may have not been initialized
...
Try that on for size. That "true" after file.txt means it will append to what file you've found.
Here's a link to the documentation. Take note of the last constructor for FileWriter.
BufferedReader br = null;
To fix your current error changing your first line to this would be how you do it. That reader however is not needed whatsoever.
I have a list of some commands stored in an ArrayList and I have been trying to get this list printed in a text file. Below is the code-
try {
FileWriter writer = new FileWriter("Commands.txt");
for(String str: commandArray){
writer.write(commandArray[i]);
}
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
I get no errors but the file isn't created either. Is there something I have done wrong. Any help is appreciated. Many thanks.
EDITED QUESTION
#Sajal Dutta, I took your advice and came up with the following;
try {
for(String str: movementArray){
File file = new File("D://filename.txt");
// if file doesnt exists, then create it
if (!file.exists()) {
file.createNewFile();
}
FileWriter fw = new FileWriter(file.getAbsoluteFile());
BufferedWriter bw = new BufferedWriter(fw);
bw.write(str);
bw.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
At The moment the file is created, but only the last value of from the arraylist is printed to the file. There are six values stored in the arraylist, how do I get all six of the to print out?
You are missing-
finally {
writer.close();
}
try {
if(!file.exists())
file.createNewFile();
FileWriter writer = new FileWriter(file);
BufferedWriter bw = new BufferedWriter(writer);
for(String str : data){
bw.append(str);
bw.append("\n");
}
bw.close();
writer.close();
}
Each time in the for loop you are creating a new FileWriter & BufferedWriter object which is not good
I am developing a java application in which I need to save some data in a file. I tried to use different methods, however no file gets saved and I don't receive any errors. Here is my code for saving the file:
String filename = "/Users/name.txt";
FileWriter fstream;
try {
fstream = new FileWriter(filename);
BufferedWriter out = new BufferedWriter(fstream);
out.write("My Name is Bobby Bob");
out.newLine();
out.flush();
out.close();
}
catch (IOException e) {
e.printStackTrace();
}
I tried even making the file myself but it remains empty.
It's unlikely that you can write directly to the Users folder through Java on Mac OSX.
Try this to make sure:
String filename = "/Users/name.txt";
FileWriter fstream;
try {
File file = new File(filename);
// checking if we can write this file
System.out.println("Can write? " + file.canWrite());
fstream = new FileWriter(file);
BufferedWriter out = new BufferedWriter(fstream);
out.write("My Name is Bobby Bob");
out.newLine();
out.flush();
out.close();
} catch (IOException e) {
e.printStackTrace();
}
Output expected:
Can write? false