Java:PrintWriter未在文件中写入
我遇到了一些关于Java:PrintWriter未在文件中写入,java,outputstream,fileoutputstream,printwriter,Java,Outputstream,Fileoutputstream,Printwriter,我遇到了一些关于PrintWriter的问题。我编写了一些代码,只需从一个文件中获取一些输入并将其输出到另一个文件 虽然创建了一个文件,但该文件仍然为空。所需的输入可以在控制台中轻松打印出来,这意味着FileInputStream工作正常 为什么PrintWriter不打印任何东西 public static void writeInFile(File in, File out) throws FileNotFoundException { PrintWriter outputStrea
PrintWriter
的问题。我编写了一些代码,只需从一个文件中获取一些输入并将其输出到另一个文件
虽然创建了一个文件,但该文件仍然为空。所需的输入可以在控制台中轻松打印出来,这意味着FileInputStream工作正常
为什么PrintWriter不打印任何东西
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();
}
确保始终关闭
输出流
:
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();
编辑:当您关闭它自动调用的输出流flush
时,它会将缓冲区写入文件。如果不关闭它,缓冲区可能永远不会被清空/写入文件,就像这里的情况一样
另请参见。在处理需要清理的IO时,我更喜欢使用自动资源清理。这就是您在最基本的层面上所需要的:
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");
}
}
}
现在可以通过多种方式重载此函数:
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);
}
}
看起来您从未在第二种方法中关闭输出流。您可能希望在WriteInFile中检查scanner.hasNextLine()
,而不是scanner.hasNext()
,因为您正在使用scanner.nextLine()