Question

我需要创建一个JavaFX项目，创建一个gui来输入名称和密码。我创建了窗格，并设置了舞台。项目显示正确，但我无法点击按钮获取信息写入文件。它会创建文件但不会存储数据。我需要能够使用多个名称和密码，因此我可以创建一个读者登录程序来检查.txt文件。这是我的代码。谢谢。

import javax.swing.JOptionPane;
import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.geometry.HPos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

import java.io.*;

public class AddUser extends Application {
    private TextField tfUsername = new TextField();
    private TextField tfPassword = new TextField();
    private Button btAddUser = new Button("Add User");
    private Button btClear = new Button("Clear");

    @Override // Override the start method in the Application class
    public void start(Stage primaryStage) {
        // Create UI
        GridPane gridPane = new GridPane();
        gridPane.setHgap(5);
        gridPane.setVgap(5);
        gridPane.add(new Label("Username:"), 0, 0);
        gridPane.add(tfUsername, 1, 0);
        gridPane.add(new Label("Password:"), 0, 1);
        gridPane.add(tfPassword, 1, 1);
        gridPane.add(btAddUser, 1, 3);
        gridPane.add(btClear, 1, 3);

        // Set properties for UI
        gridPane.setAlignment(Pos.CENTER);
        tfUsername.setAlignment(Pos.BOTTOM_RIGHT);
        tfPassword.setAlignment(Pos.BOTTOM_RIGHT);

        GridPane.setHalignment(btAddUser, HPos.LEFT);
        GridPane.setHalignment(btClear, HPos.RIGHT);

        // Process events
        btAddUser.setOnAction(e -> writeNewUser());

        btClear.setOnAction(e -> {
            tfUsername.clear();
            tfPassword.clear();
        });   

        // Create a scene and place it in the stage
        Scene scene = new Scene(gridPane, 300, 150);
        primaryStage.setTitle("Add User"); // Set title
        primaryStage.setScene(scene); // Place the scene in the stage
        primaryStage.show(); // Display the stage
    }

    public void writeNewUser() {      
        PrintWriter fw = null;

        try {
            fw = new PrintWriter("users.txt");
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write(tfUsername.getText());
            bw.newLine();
            bw.write(tfPassword.getText());
            fw.close();
        } catch (IOException e) {
            e.printStackTrace();

        }
    }

    /**
     * The main method is only needed for the IDE with limited
     * JavaFX support. Not needed for running from the command line.
     */
    public static void main(String[] args) {
        launch(args);
    }
}

Answer 1

您是“原创的”在fw.close方法的catch块的try-catch块中有writeNewUser方法......

public void writeNewUser() {      
    PrintWriter fw = null;
    try {
        fw = new PrintWriter("users.txt");
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(tfUsername.getText());
        bw.newLine();
        bw.write(tfPassword.getText());
    } catch (IOException e) {
        e.printStackTrace();
        fw.close();
    }
}

正如已经指出的那样，只有在出现问题时才会调用此方法。此外，PrintWriter#close会引发IOException而fw可能会null，从而导致更多问题......

修改后的代码只是稍微好一些......

public void writeNewUser() {      
    PrintWriter fw = null;
    try {
        //....
        fw.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

将close电话放在try部分内意味着只有一切顺利才能调用它。如果由于某种原因发生异常，则永远不会关闭资源

您还应该关闭外部资源，在这种情况下为BufferedWriter，这会将对每个封闭资源的近距离调用链接起来。

相反，您应该使用try-with-resources，它会自动关闭资源，例如......

public void writeNewUser() {
    try (BufferedWriter bw = new BufferedWriter(new PrintWriter("users.txt"))) {
        bw.write(tfUsername.getText());
        bw.newLine();
        bw.write(tfPassword.getText());
    } catch (IOException e) {
        e.printStackTrace();

    }
}

请查看The try-with-resources Statement了解详情

<强>更新

要附加到该文件，您可能需要使用FileWriter代替，例如......

public void writeNewUser() {
    try (BufferedWriter bw = new BufferedWriter(new FileWriter("users.txt", true))) {
        bw.write(tfUsername.getText());
        bw.newLine();
        bw.write(tfPassword.getText());
        bw.newLine();
    } catch (IOException e) {
        e.printStackTrace();

    }
}

Answer 2

问题出在writeNewUser方法中：

public void writeNewUser() {

    PrintWriter fw = null;

    try {
        fw = new PrintWriter("users.txt");
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(tfUsername.getText());
        bw.newLine();
        bw.write(tfPassword.getText());
    } catch (IOException e) {
        e.printStackTrace();
        fw.close();    
    }
}

fw.close（）在catch循环中，但问题是它只在出现错误时关闭（这就是为什么有一个catch块）

解决此问题：

public void writeNewUser() {

    PrintWriter fw = null;

    try {
        fw = new PrintWriter("users.txt");
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(tfUsername.getText());
        bw.newLine();
        bw.write(tfPassword.getText());
        fw.close();
    } catch (IOException e) {
        e.printStackTrace();   
        fw.close 
    }
}

^^将fw.close（）放在try和catch块中。

至于使其可重复，请尝试在初始化FileWriter之前将密码和用户名（使用scanner类）保存到数组中，然后使用for循环将数组重写到文件中。

希望这会有所帮助：经典

需要JavaFX帮助写入.txt文件

2 个答案: