[英]How to append text to an existing file in Java?
我需要將文本重復附加到 Java 中的現有文件中。 我怎么做?
你這樣做是為了記錄目的嗎? 如果是這樣,那么有幾個庫。 其中最流行的兩個是Log4j和Logback 。
對於一次性任務, Files 類使這很容易:
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:如果文件不存在,上述方法將拋出NoSuchFileException
。 它也不會自動附加換行符(在附加到文本文件時通常需要)。 另一種方法是同時傳遞CREATE
和APPEND
選項,如果文件不存在,它將首先創建文件:
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,如果您將多次寫入同一個文件,則上述代碼段必須多次打開和關閉磁盤上的文件,這是一個緩慢的操作。 在這種情況下, 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
}
筆記:
FileWriter
構造函數的第二個參數將告訴它追加到文件,而不是寫入新文件。 (如果文件不存在,將被創建。)FileWriter
),建議使用BufferedWriter
。PrintWriter
可以讓您訪問您可能從System.out
習慣的println
語法。BufferedWriter
和PrintWriter
包裝器並不是絕對必要的。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
}
如果您需要對舊 Java 進行強大的異常處理,它會變得非常冗長:
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
}
}
您可以使用將標志設置為true
的fileWriter
進行追加。
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());
}
這里的所有 try/catch 塊的答案不應該都包含在 finally 塊中的 .close() 片段嗎?
標記答案的示例:
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,從 Java 7 開始,您可以使用try-with-resources 語句。 關閉聲明的資源不需要 finally 塊,因為它是自動處理的,而且也不那么冗長:
try(PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("writePath", true)))) {
out.println("the text");
} catch (IOException e) {
System.err.println(e);
}
使用 Apache Commons 2.1:
import org.apache.logging.log4j.core.util.FileUtils;
FileUtils.writeStringToFile(file, "String to append", true);
稍微擴展Kip 的答案,這是一個簡單的 Java 7+ 方法,用於將新行附加到文件,如果它不存在則創建它:
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...
}
進一步說明:
上面使用了將文本行寫入文件的Files.write
重載(即類似於println
命令)。 要將文本寫入末尾(即類似於print
命令),可以使用替代的Files.write
重載,傳入一個字節數組(例如"mytext".getBytes(StandardCharsets.UTF_8)
)。
CREATE
選項僅在指定目錄已存在時才有效 - 如果不存在,則拋出NoSuchFileException
。 如果需要,可以在設置path
后添加以下代碼來創建目錄結構:
Path pathParent = path.getParent(); if (!Files.exists(pathParent)) { Files.createDirectories(pathParent); }
令人擔憂的是,這些答案中有多少會在出現錯誤時使文件句柄保持打開狀態。 答案https://stackoverflow.com/a/15053443/2498188很划算,但這只是因為BufferedWriter()
不能拋出。 如果可以,則異常將使FileWriter
對象保持打開狀態。
一種更通用的方法,它不關心BufferedWriter()
是否可以拋出:
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
}
}
從 Java 7 開始,推薦的方法是使用“try with resources”並讓 JVM 處理它:
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 中也可以這樣做:
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);
爪哇 7+
以我的拙見,因為我是普通 java 的粉絲,所以我建議它是上述答案的組合。 也許我參加聚會遲到了。 這是代碼:
String sampleText = "test" + System.getProperty("line.separator");
Files.write(Paths.get(filePath), sampleText.getBytes(StandardCharsets.UTF_8),
StandardOpenOption.CREATE, StandardOpenOption.APPEND);
如果文件不存在,它會創建它,如果已經存在,它會將sampleText附加到現有文件中。 使用它,可以避免將不必要的庫添加到類路徑中。
這可以在一行代碼中完成。 希望這可以幫助 :)
Files.write(Paths.get(fileName), msg.getBytes(), StandardOpenOption.APPEND);
我只是添加一些小細節:
new FileWriter("outfilename", true)
2.nd 參數 (true) 是稱為可附加( http://docs.oracle.com/javase/7/docs/api/java/lang/Appendable.html ) 的功能(或接口)。 它負責能夠將一些內容添加到特定文件/流的末尾。 這個接口是從 Java 1.5 開始實現的。 ) with this interface can be used for adding content每個具有此接口的對象(即 )都可以用於添加內容
換句話說,您可以將一些內容添加到您的 gzip 文件中,或者一些 http 進程
使用 java.nio。 文件連同 java.nio.file。 標准開放選項
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();
這將使用 Files 創建一個BufferedWriter
,它接受StandardOpenOption
參數,以及來自結果BufferedWriter
的自動刷新PrintWriter
。 然后可以調用PrintWriter
的println()
方法來寫入文件。
此代碼中使用的StandardOpenOption
參數:打開文件進行寫入,僅附加到文件,如果文件不存在則創建文件。
Paths.get("path here")
可以替換為new File("path here").toPath()
。 並且Charset.forName("charset name")
可以修改以適應所需的Charset
。
示例,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);
}
嘗試使用 bufferFileWriter.append,它適用於我。
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);
}
FileOutputStream fos = new FileOutputStream("File_Name", true);
fos.write(data);
true 允許在現有文件中附加數據。 如果我們寫
FileOutputStream fos = new FileOutputStream("File_Name");
它將覆蓋現有文件。 所以選擇第一種方法。
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.
}
}
}
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();
}
這將做你想要的..
你也可以試試這個:
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
}
最好使用 try-with-resources 然后所有 pre-java 7 最終業務
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();
}
}
如果我們使用 Java 7 及以上版本並且知道要添加(附加)到文件中的內容,我們可以使用 NIO 包中的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();
}
}
有幾點需要注意:
StandardCharsets
類中有常量。try-with-resource
語句,其中資源在嘗試后自動關閉。 雖然 OP 沒有詢問,但如果我們想搜索具有某些特定關鍵字的行,例如confidential
,我們可以在 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();
}
FileOutputStream stream = new FileOutputStream(path, true);
try {
stream.write(
string.getBytes("UTF-8") // Choose your encoding.
);
} finally {
stream.close();
}
然后在上游某處捕獲 IOException。
在項目的任何地方創建一個函數,然后在需要的地方調用該函數。
伙計們,你們必須記住,你們正在調用不是異步調用的活動線程,因為要正確完成它可能需要 5 到 10 頁。 為什么不花更多的時間在你的項目上,忘記寫任何已經寫好的東西。 適當地
//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********/
三行代碼實際上是第二行,因為第三行實際上附加了文本。 :P
圖書館
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
代碼
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);
}
}
我可能會建議apache commons 項目。 這個項目已經提供了一個框架來做你需要的(即靈活的集合過濾)。
以下方法可讓您將文本附加到某個文件:
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);
}
它效率不高,但工作正常。 換行符被正確處理,如果一個新文件尚不存在,則會創建一個新文件。
此代碼將滿足您的需求:
FileWriter fw=new FileWriter("C:\\file.json",true);
fw.write("ssssss");
fw.close();
如果您想在特定行中添加一些文本,您可以首先閱讀整個文件,將文本附加到您想要的任何位置,然后覆蓋下面代碼中的所有內容:
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
}
/**********************************************************************
* 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()
對於 JDK 版本 >= 7
您可以利用這個簡單的方法將給定的內容附加到指定的文件:
void appendToFile(String filePath, String content) {
try (FileWriter fw = new FileWriter(filePath, true)) {
fw.write(content + System.lineSeparator());
} catch (IOException e) {
// TODO handle exception
}
}
我們正在附加模式下構造一個FileWriter對象。
您可以使用以下代碼將內容附加到文件中:
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);
}*/
}
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