使用 BufferedReader 和 FileReader；文件正在读取但不输出其内容？答案

【问题标题】：Using BufferedReader and FileReader; File is reading but not outputting its contents?使用 BufferedReader 和 FileReader；文件正在读取但不输出其内容？
【发布时间】：2016-11-26 16:36:56
【问题描述】：

我编写了一个程序，它应该使用BufferedReader 和FileReader 类读取外部文件。它识别文件并成功构建，但它不会打印出它应该在其中执行的文本文件的内容。代码如下：

计划

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);
            }
        }
    }
}

应该打印出来的文件内容如下：

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

实际输出

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

非常感谢任何有关解决此问题的帮助，谢谢。

【问题讨论】：

这段代码编译了吗？你的第一个 catch 块没有在那里关闭。还是错字？
提示：在 IDE 中正确格式化所有代码，以便缩进对您有所帮助。然后看看你的while 循环在哪里。我建议删除 all 您的 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在了错误的位置。经过缩进并正确格式化后，我发现了错误，谢谢。

标签： java bufferedreader filereader

【解决方案1】：

第一个 catch 语句没有结束括号，因此文件读取器位于 catch 语句内。

【讨论】：

【解决方案2】：

您仅在抛出 FileNotFoundException 时才尝试读取文件。此外，您应该在使用资源后关闭它们。那这个呢？

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");
    }
}

【讨论】：

【解决方案3】：

您已尝试在 FileNotFoundException 的异常分支中读取文件。这意味着，您的程序仅在未找到该文件时才读取该文件，这是没有意义的。它的工作原理是这样的：

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.");
    }

}

附带说明，您应该始终关闭您使用的资源，在这种情况下，您的文件由FileReader 打开，如上面finally 分支中所示。此外，您无需致电System.exit(0)。

【讨论】：

【解决方案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);
                }
        }

【讨论】：