java - 如何打印到文件？

Question

我正在完成一项任务并且遇到了一些障碍。

我的程序将输出打印到屏幕上(不是我需要的)，但只打印文件的第一个条目。下面是代码片段。该文件似乎正在从输入文件中读取数据，但循环不会在第一个条目之后输出到文件。

Scanner in = new Scanner(System.in);    //Scanner object to read input from the file
System.out.println("Enter filename to read ");  //file name prompt  
String inputFileName = in.nextLine();                //line input reads next line

/*
 * TODO 2) Use an unbuffered file input stream to open listings.txt file
 * and read in property listings.
 */
Scanner reader = null;
try {
    reader = new Scanner(new File(inputFileName));
} catch (FileNotFoundException e) {

    System.out.println("Try Again");   //error window if name is null
    JOptionPane.showMessageDialog(null, "You must enter a filename", "File input error", JOptionPane.ERROR_MESSAGE);
    return;

}

PrintWriter out = new PrintWriter("agentreport.txt"); //This method prints out the file readfile.txt a word at a time
while (reader.hasNextLine()) {                      //It needs to output to the text file. Currently a file is created, but it is empty?
    Scanner s2 = new Scanner(reader.next());

    @SuppressWarnings("unused")
    boolean b;
    while (b = s2.hasNext()) {
        String output = s2.next();
        String output2 = output.toUpperCase(); //converts output to upper case
        System.out.println(output2);
        out.print(output2);  //only printing the first entry to the agentsreport.txt file. Not stepping thru the file for some reason? 
   }

Answer 1

即使您正在使用自动刷新(在这种情况下不是这样)，PrintWriter 对象也会在其内部缓冲区中输出任何内容，除非您执行以下两项操作之一:

1) 使用 println() , printf() , 或 format()方法

2) 调用flush()每次打印时方法，这样内部缓冲区中的所有数据都会被写出。

注意:print()方法不会导致 PrintWriter 对象为 flush()它的缓冲区。

尝试添加对 flush() 的调用在您调用 print() 之后

split() 示例

PrintWriter out = new PrintWriter("agentreport.txt"); 
while (reader.hasNextLine()) {                    
    String words = reader.nextLine().split();

    @SuppressWarnings("unused")
    boolean b;
    for(String word : words) {
        String output = word ;
        String output2 = output.toUpperCase(); //converts output to upper case
        System.out.println(output2);
        out.print(output2);  
   }