How to append text to an existing file in Java
我需要将文本重复附加到Java中的现有文件中。 我怎么做?
你这样做是为了记录目的吗?如果是这样,那么有几个库。最受欢迎的两个是Log4j和Logback。
Java 7+
如果您只需要执行此操作,则Files类可以轻松实现:
1 2 3 4 5 | 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,上面的方法将抛出
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:
1 2 3 4 5 6 7 8 9 10 11 | 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附加到文件,而不是写入新文件。 (如果该文件不存在,则会创建该文件。) -
对于昂贵的编写器(例如
FileWriter ),建议使用BufferedWriter 。 -
使用
PrintWriter 可以访问System.out 中可能习惯的println 语法。 -
但是
BufferedWriter 和PrintWriter 包装并不是绝对必要的。
旧Java
1 2 3 4 5 6 7 | 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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 | 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
1 2 3 4 5 6 7 8 9 10 11 12 | try { String filename="MyFile.txt"; FileWriter fw = new FileWriter(filename,true); //the true will append the new data fw.write("add a line ");//appends the string to the file fw.close(); } catch(IOException ioe) { System.err.println("IOException:" + ioe.getMessage()); } |
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:
1 2 3 4 5 6 7 8 9 10 11 | 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:
1 2 3 4 5 | 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:
1 | 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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | 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(); } } } |
S>
为了略微扩展基普的答案,
这是一个简单的Java 7+方法,用于将新行附加到文件中,如果它尚不存在则创建它:
1 2 3 4 5 6 7 | 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
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
执行此操作的更一般方法不关心
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | 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:
1 2 3 4 5 6 7 8 | 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中它也可以这样做:
1 2 3 4 | import java.nio.file.Files; import java.nio.file.Path; import java.nio.file.Paths; import java.nio.file.StandardOpenOption; |
// ---------------------
1 2 3 4 5 | 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+
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:
1 2 3 |
如果该文件不存在,则创建该文件,如果该文件已存在,则附加该文件
sampleText到现有文件。使用它,可以避免在类路径中添加不必要的库。
这可以在一行代码中完成。希望这可以帮助 :)
1 | Files.write(Paths.get(fileName), msg.getBytes(), StandardOpenOption.APPEND); |
使用java.nio.Files和java.nio.file.StandardOpenOption
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | 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
此代码中使用的
并且可以修改
我只是添加小细节:
1 |
2.nd参数(true)是一个名为appendable的特性(或接口)(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。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)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
样品,使用番石榴:
1 2 3 4 5 6 7 |
尝试使用bufferFileWriter.append,它适用于我。
1 2 3 4 5 6 7 8 9 10 | 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); } |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | 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..
最好使用try-with-resources然后所有java-7之前的业务
1 2 3 4 5 6 | 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)到文件的内容,我们可以在NIO包中使用newBufferedWriter方法。
1 2 3 4 5 6 7 8 9 10 11 12 | public static void main(String[] args) { Path FILE_PATH = Paths.get("C:/temp","temp.txt"); String text =" 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:
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
1 2 3 4 5 6 7 8 9 10 | //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(); } |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | 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. } } } |
Library
1 2 3 4 | import java.io.BufferedWriter; import java.io.File; import java.io.FileWriter; import java.io.IOException; |
Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | 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); } } |
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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | //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
1 2 3 4 5 6 7 8 9 10 11 12 | 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。
1 2 |
true允许将数据附加到现有文件中。如果我们会写
1 |
它将覆盖现有文件。所以去第一个方法。
你也可以试试这个:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | 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 } |
以下方法让您将文本追加到某个文件:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | 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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | 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)。
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)。
此代码将满足您的需求:
1 2 3 |
如果您想在特定线路中添加某些文本,您可以先读取整个文件,在任意位置附加文本,然后覆盖以下代码中的所有内容:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 | 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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | 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 } |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | /********************************************************************** * 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() |
1.7方法:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | 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); }*/ } |
您可以使用follong代码将内容附加到文件中:
1 2 3 4 5 6 7 | 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(); |