如何在Java中将文本追加到现有文件

我需要将文本重复添加到Java中的现有文件中。我怎么做？

您是否出于记录目的这样做？如果是这样，则有几个库。最受欢迎的两个是Log4j和Logback。

Java 7+

如果您只需要执行一次，则使用Files类很容易：

try {
    Files.write(Paths.get("myfile.txt"), "the text".getBytes(), StandardOpenOption.APPEND);
}catch (IOException e) {
    //exception handling left as an exercise for the reader
}

^{注意：NoSuchFileException如果文件不存在，上述方法将抛出。它还不会自动追加换行符（追加到文本文件时通常会需要此换行符）。史蒂夫·钱伯斯（Steve Chambers）的答案涵盖了如何在Files课堂上做到这一点。}

但是，如果您要多次写入同一文件，则上述操作必须多次打开和关闭磁盘上的文件，这是一个缓慢的操作。在这种情况下，使用缓冲写入器更好：

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
}

笔记：

• FileWriter构造函数的第二个参数将告诉它追加到文件中，而不是写入新文件。（如果文件不存在，将创建它。）
• BufferedWriter对于昂贵的作家（例如FileWriter），建议使用。
• 使用a PrintWriter可访问println您可能习惯使用的语法System.out。
• 但是BufferedWriter和PrintWriter包装并不是严格必要的。

较旧的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
}

异常处理

如果您需要对旧版Java进行健壮的异常处理，它将变得非常冗长：

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
    }
}

您可以将fileWriter标志设置为true进行添加。

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());
}

这里不是所有关于try / catch块的答案都在finally块中包含.close（）块吗？

标记答案的示例：

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();
    }
} 

另外，从Java 7开始，您可以使用try-with-resources语句。不需要finally块来关闭已声明的资源，因为它是自动处理的，并且也不太冗长：

try(PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)))) {
    out.println("the text");
} catch (IOException e) {
    System.err.println(e);
}

编辑 -从Apache Commons 2.1开始，正确的方法是：

FileUtils.writeStringToFile(file, "String to append", true);

我修改了@Kip的解决方案，以包括最终正确关闭文件：

public static void appendToFile(String targetFile, String s) throws IOException {
    appendToFile(new File(targetFile), s);
}

public static void appendToFile(File targetFile, String s) throws IOException {
    PrintWriter out = null;
    try {
        out = new PrintWriter(new BufferedWriter(new FileWriter(targetFile, true)));
        out.println(s);
    } finally {
        if (out != null) {
            out.close();
        }
    }
}

为了稍微扩展Kip的答案，这是一个简单的Java 7+方法，用于在文件中添加新行，如果尚不存在，则创建该行：

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...
}

注意：上面的方法使用了Files.write将文本行写入文件的重载（即类似于println命令）。要将文本仅写到末尾（即类似于print命令），Files.write可以使用替代的重载，传入字节数组（例如"mytext".getBytes(StandardCharsets.UTF_8)）。

确保在所有情况下均正确关闭流。

这有点令人震惊，以防万一发生错误，其中有多少答案使文件句柄保持打开状态。答案https://stackoverflow.com/a/15053443/2498188可以赚钱，但这仅仅是因为BufferedWriter()不能抛出。如果可能，则异常将使FileWriter对象保持打开状态。

一种更通用的方法，不管是否BufferedWriter()会抛出：

  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
     }
  }

编辑：

从Java 7开始，推荐的方法是使用“尝试资源”并让JVM处理：

  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.
  }

在Java-7中，也可以这样做：

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+

根据我的愚见，因为我是纯Java的粉丝，所以我建议将上述答案组合在一起。也许我参加聚会迟到了。这是代码：

 String sampleText = "test" +  System.getProperty("line.separator");
 Files.write(Paths.get(filePath), sampleText.getBytes(StandardCharsets.UTF_8), 
 StandardOpenOption.CREATE, StandardOpenOption.APPEND);

如果该文件不存在，则创建它，如果已经存在，则将sampleText附加 到现有文件中。使用此方法，可以避免将不必要的库添加到类路径中。

可以用一行代码完成。希望这可以帮助 ：）

Files.write(Paths.get(fileName), msg.getBytes(), StandardOpenOption.APPEND);

使用java.nio。文件以及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();

这产生了BufferedWriter使用的文件，它接受StandardOpenOption参数，和自动冲洗PrintWriter从所得BufferedWriter。然后可以调用PrintWriter的println()方法写入文件。

StandardOpenOption此代码中使用的参数：打开文件进行写入，仅追加到文件，如果文件不存在则创建文件。

Paths.get("path here")可以替换为new File("path here").toPath()。并Charset.forName("charset name")可以进行修改以适应所需Charset。

我只添加一些小细节：

    new FileWriter("outfilename", true)

2.nd参数（true）是一个称为appendable（http://docs.oracle.com/javase/7/docs/api/java/lang/Appendable.html）的功能（或接口）。它负责将某些内容添加到特定文件/流的末尾。此接口从Java 1.5开始实现。带有此接口的每个对象（即BufferedWriter，CharArrayWriter，CharBuffer，FileWriter，FilterWriter，LogStream，OutputStreamWriter，PipedWriter，PrintStream，PrintWriter，StringBuffer，StringBuilder，StringWriter，Writer）都可以用于添加内容

换句话说，您可以将一些内容添加到压缩文件中，或添加一些http进程

示例，使用番石榴：

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);
}

尝试使用bufferFileWriter.append，它对我有用。

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);
}

    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();         
    }

这将满足您的预期。

最好使用try-with-resources，然后再使用Java 7之前的所有产品

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();
    }
}

如果我们使用Java 7及更高版本，并且还知道要添加（附加）到文件中的内容，则可以使用NIO包中的newBufferedWriter方法。

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();
    }
}

有几点要注意：

1. 指定charset编码始终是一个好习惯，为此我们在类中具有常量StandardCharsets。
2. 该代码使用try-with-resource语句，其中的资源在尝试后会自动关闭。

尽管OP并没有要求，但以防万一我们想搜索具有某些特定关键字的行，例如，confidential我们可以使用Java中的流API：

//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 fos = new FileOutputStream("File_Name", true);
fos.write(data);

true允许将数据追加到现有文件中。如果我们写

FileOutputStream fos = new FileOutputStream("File_Name");

它将覆盖现有文件。因此，采用第一种方法。

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.
        }

    }

}

FileOutputStream stream = new FileOutputStream(path, true);
try {

    stream.write(

        string.getBytes("UTF-8") // Choose your encoding.

    );

} finally {
    stream.close();
}

然后在上游某处捕获IOException。

在项目中的任何位置创建一个函数，并在需要时直接调用该函数。

你们要记住，你们正在调用的活动线程不是异步调用的，因为正确完成该任务可能需要5到10页。为什么不花更多的时间在您的项目上，而忘记写任何已经写的东西。正确地

    //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********/

第三行代码实际上是第二行，因为第三行实际上是在追加文本。：P

图书馆

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

码

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);
    }
}

您也可以尝试以下方法：

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
}

我可能会建议apache commons项目。该项目已经提供了执行所需操作的框架（即，集合的灵活过滤）。

以下方法让您将文本追加到某个文件：

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();
        }
    }
}

或者使用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);
}

它效率不高，但效果很好。换行符已正确处理，如果尚不存在，则会创建一个新文件。

这段代码将满足您的需求：

   FileWriter fw=new FileWriter("C:\\file.json",true);
   fw.write("ssssss");
   fw.close();

如果要在特定行中添加某些文本，则可以先阅读整个文件，然后将文本附加到所需的位置，然后覆盖以下代码中的所有内容：

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();
    }
}

我的答案：

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()

您可以使用follong代码将内容附加到文件中：

 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(); 

1.7方法：

void appendToFile(String filePath, String content) throws IOException{

    Path path = Paths.get(filePath);

    try (BufferedWriter writer = 
            Files.newBufferedWriter(path, 
                    StandardOpenOption.APPEND)) {
        writer.newLine();
        writer.append(content);
    }

    /*
    //Alternative:
    try (BufferedWriter bWriter = 
            Files.newBufferedWriter(path, 
                    StandardOpenOption.WRITE, StandardOpenOption.APPEND);
            PrintWriter pWriter = new PrintWriter(bWriter)
            ) {
        pWriter.println();//to have println() style instead of newLine();   
        pWriter.append(content);//Also, bWriter.append(content);
    }*/
}