[英]Java: PrintWriter not writing in file
我遇到了PrintWriter
一些問題。 我編寫了一些代碼,這些代碼僅從文件中獲取一些輸入並將其輸出到另一個文件。
盡管已創建文件,但該文件仍為空。 所需的輸入可以輕松地在控制台中打印出來,這意味着FileInputStream可以正常工作。
為什么PrintWriter不打印任何內容?
public static void writeInFile(File in, File out) throws FileNotFoundException {
PrintWriter outputStream = null
Scanner scanner = new Scanner(new FileInputStream(in));
outputStream = new PrintWriter(new FileOutputStream(out));
outputStream.print("test");
while(scanner.hasNext()) {
outputStream.print(scanner.nextLine() + "\n");
}
scanner.close();
}
確保您始終關閉OutputStreams
:
while(scanner.hasNext()) {
String s = scanner.nextLine();
outputStream.print(s+"\n");
System.out.println("Test "+s); //d.h. das Problem liegt am outputstream
}
outputStream.close();
scanner.close();
編輯: close
outputStream時,它將自動調用flush
,這會將緩沖區寫入文件。 如果不關閉它,緩沖區可能永遠不會清空/寫入文件,就像這里的情況。
另請參閱此答案 。
在處理需要清理的IO時,我更喜歡使用自動資源清理。 這是最基本的需求:
public static void writeInToOut(InputStream in, OutputStream out) {
try(PrintWriter outputStream = new PrintWriter(out);
Scanner scanner = new Scanner(in)) {
while(scanner.hasNext()) {
outputStream.print(scanner.nextLine()+"\n");
}
}
}
您現在可以通過幾種方式重載此函數:
public static void writeInToOut(File file, OutputStream out) {
try (InputStream in = new FileInputStream(file)) {
writeInToOut(in, out);
} catch (IOException e) {
Logger.getAnonymousLogger().log(Level.WARNING, "IOError", e);
}
}
public static void writeInToOut(File inFile, File outFile) {
try (InputStream in = new FileInputStream(inFile);
OutputStream out = new FileOutputStream(outFile)) {
writeInToOut(in, out);
} catch (IOException e) {
Logger.getAnonymousLogger().log(Level.WARNING, "IOError", e);
}
}
public static void writeStdInToFile(File file) {
try (OutputStream out = new FileOutputStream(file)) {
writeInToOut(System.in, out);
} catch (IOException e) {
Logger.getAnonymousLogger().log(Level.WARNING, "IOError", e);
}
}
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