Java 如何使用 FileReader 逐行读取

How to read line by line by using FileReader

提问by Ender phan

Thank you for your attention.

感谢您的关注。

I have created a program which I'm using a Login form and Register form. Once users register their email and their password will be saved it into submit.txt. Then they will turn back to login form and enter their email and password which are saved into submit.txt.

我创建了一个程序，我正在使用登录表单和注册表单。一旦用户注册了他们的电子邮件，他们的密码就会被保存到submit.txt. 然后他们将返回登录表单并输入保存在submit.txt.

In my code, I'm using write file for Register form, and Read file for Login Form. But, it doesn't work. I know my problem in the code used for Read File. May you help me to realize that?.

在我的代码中，我对注册表单使用写入文件，对登录表单使用读取文件。但是，它不起作用。我知道我在用于读取文件的代码中的问题。你能帮我意识到这一点吗？

Thank you too much for your help.

非常感谢您的帮助。

 if (checkPassword(usern, hash)) {
    System.out.println("Logged in!");
    ChooseWindow ptb = new ChooseWindow();
    ptb.setVisible(true);
    LoginWindow.this.dispose();
 } else {
    System.out.println("Wrong password");
 }

 public boolean checkPassword(String username, String pass) {
    try {
        FileReader inFile = new  FileReader("/users/Ender/Desktop/GetUser/submit.txt");
        BufferedReader inStream = new BufferedReader(inFile);
        String inString;

        while ((inString = inStream.readLine()) != null) {}
        inStream.close();                       
    }catch (IOException e) {
        e.printStackTrace();
    }
    return false;
 }

采纳答案by Ahmad Alkhatib

here is my code to read from a file :

这是我从文件中读取的代码：

 String line;

    try {

        BufferedReader bufferreader = new BufferedReader(new FileReader("C:\Users\ahmad\Desktop\aaa.TXT"));


        while ((line = bufferreader.readLine()) != null) {     
          /** 
            Your implementation  
          **/

        }

    } catch (FileNotFoundException ex) {
        ex.printStackTrace();
    } catch (IOException ex) {
        ex.printStackTrace();
    }

回答by Ramesh-X

You can read a file using following code..

您可以使用以下代码读取文件..

    try {
        BufferedReader bufferreader = new BufferedReader(new FileReader("./users/Ender/Desktop/GetUser/submit.txt"));
        String line;

        while ((line = bufferreader.readLine()) != null) {
            // line variable contains the readed line
            // You can append it to another String to get the whole text or anything you like
        }

    } catch (FileNotFoundException ex) {
        ex.printStackTrace();
    } catch (IOException ex) {
        ex.printStackTrace();
    }

If you want to write file use following code..

如果你想写文件使用下面的代码..

    BufferedWriter writer = new BufferedWriter(new FileWriter("./users/Ender/Desktop/GetUser/submit.txt")); 
    writer.write(your_text);
    writer.close();

If you want to append text use following code to create the instance of BufferedWriter

如果要附加文本，请使用以下代码创建 BufferedWriter

    BufferedWriter writer = new BufferedWriter(new FileWriter("/users/Ender/Desktop/GetUser/submit.txt", true)); 

回答by Aracurunir

Assuming we have a file with usernameand hashstored as follows:

假设我们有一个文件username并hash存储如下：

Hello World
Test Test
DumbUser 12345
User sjklfashm-0998()(&

Hello World
测试测试
DumbUser 12345
用户 sjklashm-0998() (&

and we want to use the first word in every line as usernameand the second as password/hash. Then the idea is:

我们想在每一行中使用第一个单词 as username，第二个单词作为password/ hash。那么思路是：

• Read a line
• Split the line into parts at " "
• Compare the first part to usernameand the second to pass
• If there is a match return true, else start over

• 读一行
• 在“ ”处将线分成几部分
• 比较第一部分username和第二部分pass
• 如果有匹配返回true，否则重新开始

Which results in this code:

这导致此代码：

public boolean checkPassword(String username, String pass) {
    // if there is no username or no password you can not log in
    if(username == null || pass == null){ // diff
        return false;                     // diff
    }                                     // diff
    try {
        FileReader inFile = new  FileReader(PASSWORD_FILE);
        BufferedReader inStream = new BufferedReader(inFile);
        String inString;

        while ((inString = inStream.readLine()) != null) {
            // we split every line into two parts separated by a space " "
            String usernameHash[] = inString.split(" "); // diff
            // if there are more or less than two parts this line is corrupted and useless
            if(usernameHash.length == 2                  // diff
                    && username.equals(usernameHash[0])  // diff
                    && pass.equals(usernameHash[1])){    // diff
                // if username matches the first part and hash the second everything is goo
                return true;                             // diff
            }                                            // diff
        }
        inStream.close();
    }catch (IOException e) {
        e.printStackTrace();
    }
    return false;
}

I marked the parts where my code differs from yours with // diff

我标记了我的代码与您的代码不同的部分 // diff