IT-Swarm.Net

如何将文本附加到的Java中的现有文件中

我需要将文本重复附加到Java中的现有文件中。我怎么做?

641
flyingfromchina

你这样做是为了记录目的吗?如果是这样的话, 有几个库 。最受欢迎的两个是 Log4jLogback 。.

Java 7+

如果您只需要执行此操作, Files class 可以轻松实现:

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 :如果文件尚不存在,上述方法将抛出NoSuchFileException。它也不会自动附加换行符(当您追加到文本文件时通常需要它)。 史蒂夫钱伯斯的回答 涵盖了如何用Files类做到这一点。.

但是,如果您要多次写入同一文件,则必须多次打开和关闭磁盘上的文件,这是一个很慢的操作。在这种情况下,缓冲编写器更好:

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
}

注意:

  • FileWriter构造函数的第二个参数将告诉它附加到文件,而不是写一个新文件。 (如果该文件不存在,则会创建该文件。)
  • 对于昂贵的编写者(例如BufferedWriter),建议使用FileWriter。.
  • 使用PrintWriter可以访问println语法,您可能已经习惯了System.out。.
  • 但是BufferedWriterPrintWriter包装并不是绝对必要的。.

旧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

如果您需要针对较旧的Java进行强大的异常处理,那么它会非常冗长:

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
    }
}
742
Kip

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您可以将fileWriter与标志设置为true一起使用,以进行追加。.

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());
}
157
northpole

不应该使用try/catch块的所有答案都包含finally块中的.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();
    }
} 

此外,从Java 7开始,您可以使用 try-with-resources语句 。关闭声明的资源不需要finally块,因为它是自动处理的,并且也不那么详细:

try(PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)))) {
    out.println("the text");
} catch (IOException e) {
    System.err.println(e);
}
66
etech

编辑 - 从Apache Commons 2.1开始,正确的方法是:

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

我改编了@Kip的解决方案,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();
        }
    }
}
40
ripper234

稍微扩展一下 Kip的答案 ,这是一个简单的Java 7+方法,用于将 换行 附加到文件中, 如果它尚不存在则创建它

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:上面使用 Files.write overload将的文本写入文件(即类似于println命令)。要只写入文本(即类似于print命令),可以使用替代的 Files.write overload,传入一个字节数组(例如"mytext".getBytes(StandardCharsets.UTF_8))。.

24
Steve Chambers

确保在所有方案中正确关闭流。.

令人担忧的是,如果出现错误,这些答案中有多少会使文件句柄保持打开状态。答案 https://stackoverflow.com/a/15053443/2498188 是钱,但只是因为BufferedWriter()不能抛出。如果可能则异常将使FileWriter对象保持打开状态。.

执行此操作的更一般方法无关心BufferedWriter()是否可以抛出:

  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.
  }
21
Emily L.

在Java-7中它也可以这样做:

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);
13
Tsolak Barseghyan

Java 7+

在我的拙见中,因为我是普通Java的粉丝,我建议它是上述答案的组合。也许我迟到了。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,则创建该文件,如果该文件已存在,则将 sampleText 附加到现有文件。使用它,可以避免在类路径中添加不必要的库。.

8
Lefteris Bab

这可以在一行代码中完成。希望这可以帮助 :)

Files.write(Paths.get(fileName), msg.getBytes(), StandardOpenOption.APPEND);
7
FlintOff

使用Java.nio. Files 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();

这将使用Files创建一个BufferedWriter,它接受StandardOpenOption参数,并从结果PrintWriter中自动刷新BufferedWriterPrintWriterprintln()方法,然后可以调用写入文件。.

此代码中使用的StandardOpenOption参数:打开要写入的文件,仅附加到文件,如果文件不存在则创建该文件。.

Paths.get("path here")可以用new File("path here").toPath()替换。并且可以修改Charset.forName("charset name")以适应所需的Charset。.

6
icasdri

我只是添加小细节:

    new FileWriter("outfilename", true)

2.nd参数(true)是一个名为 appendable http://docs.Oracle.com/javase/7/docs/api/Java/lang/Appendable。 HTML )。它负责能够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。每个对象(即 BufferedWriter,CharArrayWriter,CharBuffer,FileWriter,FilterWriter,LogStream,OutputStreamWriter,PipedWriter,PrintStream,PrintWriter,StringBuffer,StringBuilder,StringWriter,Writer)具有此接口可用于添加内容

换句话说,您可以向gzip压缩文件或某些http进程添加一些内容

5
xhudik

样品,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);
}
5
dantuch

尝试使用bufferFileWriter.append,它适用于我。.

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);
}
4
Nadhir Titaouine

最好使用try-with-resources然后所有Java 7之前的业务

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();
    }
}
3
mikeyreilly

如果我们使用Java 7及更高版本并且还知道要添加(附加)到文件的内容,我们可以在NIO包中使用 newBufferedWriter method。.

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:

  1. 指定charset编码总是一个好习惯,因为我们在类StandardCharsets中有常量。.
  2. 该代码使用try-with-resource语句,其中资源在尝试后自动关闭。.

尽管OP没有提出要求,但万一我们想要搜索具有某些特定关键字的行,例如confidential我们可以在Java中使用流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();
}
3
i_am_zero
    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();         
    }

这将做你想要的..

3
Benjamin Varghese
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.
        }

    }

}
3
David Charles
FileOutputStream fos = new FileOutputStream("File_Name", true);
fos.write(data);

true允许将数据附加到现有文件中。如果我们会写

FileOutputStream fos = new FileOutputStream("File_Name");

它将覆盖现有文件。所以去第一个方法。.

2
shakti kumar

在项目的任何位置创建一个函数,只需在需要的地方调用该函数即可。.

伙计们你必须记住,你们正在调用你不是异步调用的活动线程,因为它可能是一个很好的5到10页来完成它。为什么不在你的项目上花更多的时间而忘记写任何已写的东西。正确

    //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********/

三行代码两个真的,因为第三行实际上附加了文本。 :P

2
Netcfmx

图书馆

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

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);
    }
}
2
absiddiqueLive

你也可以试试这个:

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
}
2
aashima
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。.

2
SharkAlley

我可能会建议 Apache commons项目 。该项目已经提供了一个框架,可以满足您的需求(即灵活过滤集合)。.

1
Tom Drake

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);
}

效率不高但工作正常。正确处理换行符并创建一个新文件(如果尚未存在)。.

1
BullyWiiPlaza

如果您想要 在特定线路中添加某些文本 您可以先读取整个文件,将文本附加到您想要的任何位置,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();
    }
}
1
lfvv

此代码将满足您的需求:

   FileWriter fw=new FileWriter("C:\\file.json",true);
   fw.write("ssssss");
   fw.close();
1
Shalini Baranwal
/**********************************************************************
 * 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()
0
Mihir Patel

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
}
0
userAsh