使用BufferedReader和FileReader;文件正在讀取但不輸出其內容？

Question

我寫過一個應該使用BufferedReader和FileReader類讀取外部文件的程序。它識別文件併成功構建，但不會打印出應該執行的文本文件的內容。下面是代碼：

計劃

import java.io.BufferedReader; 
import java.io.FileNotFoundException; 
import java.io.FileReader; 
import java.io.IOException; 
import java.util.Scanner; 

public class Lab9 { 

    public static void main(String[] args) { 

     BufferedReader reader = null; 
     String line; 
     Scanner sc = new Scanner(System.in); 

     System.out.println("Please enter a file name to read"); 

     try { 
      reader = new BufferedReader(new FileReader("C:\\Users\\Lee\\Documents\\NetBeansProjects\\Lab9\\" + sc.next())); 
     } catch (FileNotFoundException ex) { 

      System.out.println(ex.getMessage() + "File was not found");   

      try { 
       while ((line = reader.readLine()) != null) 
       { 
        System.out.println(line); 
       } 
      } catch (IOException ex2) { 
       System.out.println(ex2.getMessage() + "File did not read correctly"); 
      } finally { 
       System.exit(0); 
      } 
     } 
    } 
} 

應打印出這個樣子的該文件的內容：

文件內容

By what initials was Franklin Roosevelt better known?:FDR 
Which number president was Franklin Roosevelt?:32 
Which state was Franklin Roosevelt born in?:New York 
In which year did Roosevelt become Governor of New York?:1929 
What was the name of Franklin Roosevelt's wife?:Eleanor 
How many children did Franklin Roosevelt have?:6 
From which university did Franklin Roosevelt graduate with an A.B in history?:Harvard 
What was the first name of Franklin Roosevelt's 5th cousin, who was also President?:Theodore 
Which disease is believed to be the causes of Franklin Roosevelt's paralysis?:Polio 
At what age did Franklin Roosevelt die?:63 

實際輸出

Please enter a file name to read 
Questions.txt 
BUILD SUCCESSFUL (total time: 6 seconds) 

任何幫助解決這個問題，非常感謝，謝謝。

Answer 1

您試圖讀取FileNotFoundException的例外分支中的文件。這意味着，只有當程序沒有找到時，程序纔會讀取該文件，這是沒有意義的。它的工作原理是這樣的：

public static void main(String[] args) { 

    BufferedReader reader = null; 
    String line; 
    Scanner sc = new Scanner(System.in); 

    System.out.print("Please enter a file name to read: "); 

    try { 

     reader = new BufferedReader(
       new FileReader("C:\\Users\\Lee\\Documents\\NetBeansProjects\\Lab9\\" + sc.next())); 

     try { 

      while ((line = reader.readLine()) != null) { 
       System.out.println(line); 
      } 

     } catch (IOException ex) { 
      System.out.println(
        ex.getMessage() + "File did not read correctly"); 
     } finally { 
      try { 
       if (reader != null) 
        reader.close(); 
      } catch (IOException ex) { 
       ex.printStackTrace(); 
      } 
     } 

    } catch (FileNotFoundException ex) { 
     System.out.println("File was not found."); 
    } 

} 

作爲一個側面說明，你應該總是關閉您使用的資源，在這種情況下，你的文件被打開FileReader，如finally分支上面看到的。另外，您不需要撥打System.exit(0)。

Answer 2

第一個catch語句沒有尾括號，因此文件讀取器在catch語句中。

Answer 3

您只有在引發FileNotFoundException時才嘗試讀取文件。你也應該在使用它們之後關閉資源。那這個呢？

public static void main(String[] args) throws IOException { 

    String line; 
    Scanner scanner = new Scanner(System.in); 
    System.out.println("Please enter a file name to read"); 

    try (BufferedReader reader = new BufferedReader(new FileReader("C:\\Users\\Lee\\Documents\\NetBeansProjects\\Lab9\\" + scanner.next()))) { 
     while ((line = reader.readLine()) != null) { 
      System.out.println(line); 
     } 
    } catch (FileNotFoundException fileNotFoundException) { 
     System.out.println(fileNotFoundException.getMessage() + ". File was not found"); 
    } 
} 

Answer 4

public static void main(String[] args) throws IOException { 

     BufferedReader reader = null; 
     String line; 
     Scanner sc = new Scanner(System.in); 
     System.out.println("Please enter a file name to read"); 
      reader = new BufferedReader(new FileReader(
        "C:\\Users\\Lee\\Documents\\NetBeansProjects\\Lab9\\" 
          + sc.next())); 
       while ((line = reader.readLine()) != null) { 
        System.out.println(line); 
       } 
     }