如何在 Java 中将文本附加到现有文件
-
06-07-2019 - |
题
我需要将文本重复附加到 Java 中的现有文件中。我怎么做?
解决方案
您这样做是为了记录目的吗?如果有的话有 为此有几个库. 。其中最受欢迎的两个是 Log4j 和 回溯.
Java 7+
如果您只需要执行一次此操作, 文件类 让这变得容易:
try {
Files.write(Paths.get("myfile.txt"), "the text".getBytes(), StandardOpenOption.APPEND);
}catch (IOException e) {
//exception handling left as an exercise for the reader
}
小心: :上述方法会抛出一个 NoSuchFileException
如果该文件尚不存在。它也不会自动附加换行符(在附加到文本文件时通常需要这样做)。 史蒂夫·钱伯斯的回答 涵盖了如何做到这一点 Files
班级。
但是,如果您要多次写入同一个文件,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,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:
- 第二个参数为
FileWriter
构造函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。) - 用一个
BufferedWriter
推荐给昂贵的作家(例如FileWriter
). - 用一个
PrintWriter
让您可以访问println
您可能习惯的语法System.out
. - 但是
BufferedWriter
和PrintWriter
包装器并不是绝对必要的。
旧爪哇
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
}
}
其他提示
您可以使用 fileWriter
并将标志设置为 true
,以便附加。
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());
}
这里使用try / catch块的所有答案都不应该包含finally块中的.close()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,您可以使用尝试 - with-resources声明。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);
}
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();
}
}
}
要稍微扩展 Kip的回答, 这是一个简单的Java 7+方法,用于将新行附加到文件中,创建它(如果它尚不存在):
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:以上使用 Files.write
重载将文本的行写入文件(即类似于 println
命令)。要只写文本到最后(即类似于 print
命令),另一种 Files.write 可以使用代码>
重载,传入一个字节数组(例如" mytext" .getBytes(StandardCharsets.UTF_8)
)。
确保在所有情况下都正确关闭流。
有些警告,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。答案是 https://stackoverflow.com/a/15053443/2498188 ,但仅仅是因为 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”。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 +
由于我是普通java的粉丝,我谦虚地认为,我会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,则会创建该文件,如果该文件已存在,则会附加该文件 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。希望这会有所帮助:)
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();
使用Files创建 BufferedWriter
,它接受 StandardOpenOption
参数,并从结果 BufferedWriter <中自动刷新
PrintWriter
/代码>。然后可以调用 PrintWriter
的 println()
方法来写入文件。
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(&quot; path here&quot;)
可以替换为 new File(“path here”)。toPath()
。
并且可以修改 Charset.forName(&quot; charset name&quot;)
以容纳所需的 Charset
。
我只是添加小细节:
new FileWriter("outfilename", true)
2.nd参数(true)是一个名为可附加的特征(或界面)( 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 )都可用于添加内容
换句话说,您可以向gzip压缩文件或某些http进程
添加一些内容示例,使用Guava:
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);
}
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,然后使用java 7之前的所有业务
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();
}
}
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,我们可以使用 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();
}
}
有几点需要注意:
- 指定charset编码总是一个好习惯,因为我们在类
StandardCharsets
中有常量。 - 代码使用
try-with-resource
语句,其中资源在尝试后自动关闭。
醇>
虽然OP没有询问,但是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();
}
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。
在项目的任何位置创建一个函数,只需在需要的地方调用该函数。
你要记住,你们要记住你们正在调用活动线程而不是异步调用,因为它可能是一个好的5到10页才能正确完成。 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。 适当
//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2真的是因为第三行实际附加了文本。 :P
库
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
代码
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);
}
}
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
}
FileOutputStream fos = new FileOutputStream("File_Name", true);
fos.write(data);
true允许将数据附加到现有文件中。如果我们写的话
FileOutputStream fos = new FileOutputStream("File_Name");
它将覆盖现有文件。所以先采取行动。
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)。
以下方法让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 FileUtils 代码>
:
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)。
此代码可满足您的需求:
FileWriter fw=new FileWriter("C:\\file.json",true);
fw.write("ssssss");
fw.close();
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:
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();
}
}
我的回答:
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()
您可以使用以下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);
}*/
}