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:如何在Java中向现有文件追加文本?,java,file-io,io,text-files,Java,File Io,Io,Text Files,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
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:
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。)FileWriter
- 对于昂贵的编写器(如
),建议使用FileWriter
)BufferedWriter
- 使用
可以访问PrintWriter
语法,您可能已经习惯于从println
访问该语法System.out
- 但是
和BufferedWriter
包装器并不是严格必需的PrintWriter
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:
标准字符集中使用常量
try with resource
语句,在该语句中,资源在尝试后自动关闭机密
,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
}
}