Java 使用BufferedReader和FileReader；文件正在读取但未输出其内容？

我已经编写了一个程序，应该使用

BufferedReader

和

FileReader

类读取外部文件。它可以识别文件并成功构建，但不会打印出文本文件的内容。代码如下：

节目

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);
            }
        }
    }
}

应打印的文件内容如下所示：

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.");
    }

}

文件内容

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

实际产出

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

---

非常感谢您对解决此问题的任何帮助。

您已尝试在异常分支中读取

文件NotFoundException

的文件。这意味着，只有在找不到文件时，程序才会读取该文件，这是没有意义的。它的工作原理如下：

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.");
    }

}

---

作为旁注，您应该始终关闭所使用的资源，在这种情况下，您的文件是由

FileReader

打开的，如上面的

finally

分支所示。此外，您不需要调用

System.exit（0）

第一个catch语句没有结束括号，因此文件读取器位于catch语句中。

您仅在抛出

FileNotFoundException

时才尝试读取文件。您还应该在使用资源后关闭它们。这个怎么样

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");
    }
}

---

这段代码编译了吗？你的第一个挡块没有关上。提示：在IDE中正确设置所有代码的格式，这样缩进将对您有所帮助。然后查看

while

循环的位置。我建议删除所有try/catch语句，并声明您的

main

方法可以抛出

IOException

…我将其中一个括号放错了位置。经过缩进并正确格式化后，我发现了错误，谢谢。