如何在Java中向现有文件追加文本？

我需要在Java中重复向现有文件追加文本。我该怎么做？

您这样做是为了记录日志吗？如果有的话。最受欢迎的两种是和

爪哇7+ 对于一次性任务，可以简化此操作：

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

小心：如果文件不存在，上述方法将抛出

NoSuchFileException

。它也不会自动追加换行符（在追加到文本文件时，通常需要这样做）。另一种方法是传递

CREATE

和

APPEND

选项，如果文件不存在，则首先创建文件：

private void write(final String s) throws IOException {
    Files.writeString(
        Path.of(System.getProperty("java.io.tmpdir"), "filename.txt"),
        s + System.lineSeparator(),
        CREATE, APPEND
    );
}

但是，如果要多次写入同一文件，则上述代码段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，

BufferedWriter

更快：

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
}

注意事项：

• FileWriter

  构造函数的第二个参数将告诉它附加到文件，而不是写入新文件。（如果文件不存在，将创建该文件。）
• 对于昂贵的编写器（如

  FileWriter

  ），建议使用

  BufferedWriter

  ）
• 使用

  PrintWriter

  可以访问

  println

  语法，您可能已经习惯于从

  System.out

  访问该语法
• 但是

  BufferedWriter

  和

  PrintWriter

  包装器并不是严格必需的

---

旧爪哇

---

异常处理 如果您需要对旧Java进行健壮的异常处理，它会变得非常冗长：

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
    }
}

---

您可以使用标记设置为

true

的

fileWriter

进行追加

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());
}

---

使用Apache Commons 2.1：

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

---

我只添加了一些小细节：

    new FileWriter("outfilename", true)

2.nd参数（true）是一个称为可追加的功能（或接口）。它负责将一些内容添加到特定文件/流的末尾。这个接口是从Java1.5开始实现的。具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，您可以向gzip文件或http进程添加一些内容

    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();         
    }

---

这将达到您的目的。

这里所有关于try/catch块的答案不都应该包含在finally块中的.close（）片段吗

标记答案示例：

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Java7开始，您可以使用。关闭已声明的资源不需要finally块，因为它是自动处理的，而且不太详细：

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

样本，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);
}

File to=新文件（“C:/test/test.csv”）；
对于（int i=0；i<42；i++）{
CharSequence from=“某些字符串”+i+“\n”；
append（from、to、Charsets.UTF_8）；
}

然后使用java.nio捕获上游某处的IOException。

。以及java.nio.file

这将使用文件创建一个

BufferedWriter

，该文件接受

StandardOpenOption

参数，并从生成的

BufferedWriter

中自动刷新

PrintWriter

<然后可以调用code>PrintWriter的

println（）

方法来写入文件

此代码中使用的

StandardOpenOption

参数：打开文件进行写入，仅附加到文件，如果文件不存在，则创建文件

path.get（“path here”）

可以替换为

新文件（“path here”）.toPath（）

。 和

Charset.forName（“Charset name”）

可以修改，以适应所需的

Charset

我可能会建议。这个项目已经提供了一个框架来完成您需要的工作（即灵活地筛选集合）

确保在所有场景中正确关闭流。 如果出现错误，这些答案中有多少会让文件句柄保持打开状态，这有点令人担忧。答案在于钱，但这只是因为

BufferedWriter（）

不能抛出。如果可以，则异常将使

FileWriter

对象保持打开状态

一种更通用的方法，它不关心

BufferedWriter（）

是否会抛出：

  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“try with resources”并让JVM处理它：

  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.
  }

---

在项目中的任何地方创建一个函数，并在需要时调用该函数

伙计们，你们要记住，你们在调用活动线程，而不是异步调用，因为这可能需要5到10页才能正确完成。 为什么不花更多的时间在你的项目上，忘掉已经写过的东西呢。 恰当地

代码2的三行实际上是因为第三行实际上附加了文本：P

图书馆

代码

---

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
}

---

使用try-with-resources比使用Java7之前的所有业务更好

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();
    }
}

---

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);

---

下面的方法允许您将文本附加到某个文件：

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：

---

它效率不高，但运行良好。换行符处理正确，如果还不存在，则会创建一个新文件。

尝试使用bufferFileWriter.append，它对我有效

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);
}

---

如果我们使用Java7及以上版本，并且知道要添加（附加）到文件中的内容，那么我们可以使用NIO包中的方法

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();
    }
}

有几点需要注意：

指定字符集编码始终是一个好习惯，为此，我们在类

标准字符集
中使用常量

代码使用

try with resource

语句，在该语句中，资源在尝试后自动关闭

虽然OP没有询问，但只是为了以防万一，我们希望搜索具有特定关键字的行，例如，

机密

，我们可以

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();
    }
}

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);

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();
        }
    }
}

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);
}

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);
}

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();
    }
}

//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();
}

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
}

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

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

FileOutputStream fos = new FileOutputStream("File_Name");

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

/**********************************************************************
 * 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()

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();
    }
}

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.
        }

    }

}

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...
}

Path pathParent = path.getParent();
if (!Files.exists(pathParent)) {
    Files.createDirectories(pathParent);
}

 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(); 

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

void appendToFile(String filePath, String content) {
  try (FileWriter fw = new FileWriter(filePath, true)) {
    fw.write(content + System.lineSeparator());
  } catch (IOException e) { 
    // TODO handle exception
  }
}