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java - 按下jButton时如何将数据附加到文件中

问题描述

我一直在创建一个为学生注册数据的 GUI 应用程序，数据填充在提供的 JTextfields 中。按下提交按钮后，我对其进行了编程，以我喜欢的某种方式（排列）将数据存储到文件中。对于第一次提交，程序运行良好并将数据存储到文件中，但在其他后续enter code here提交（即当学生重新填写时），程序要么覆盖，要么根本不写入文件。以下是到目前为止的代码：

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintStream;

public class StudentAssignment extends JFrame {
    private JLabel lblFname, lblbSname, lblRegNo, lblPos;
    private JButton btnsubmit;
    private JTextField txtFname, txtSname, txtRegNo, txtPos;
    private JPanel panel1, panel12, panel3, panel4,panel5;
    private int i = 1;
    private File myFile;
    private FileWriter fw;
    private PrintStream ps;


    public StudentAssignment() throws Exception{
        componentInitialization();
        setVisible(true);

        myFile =new File("Mustard.txt");

        fw = new FileWriter(myFile,true);
        ps = new PrintStream(myFile);

        actionListeners();
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void componentInitialization(){
        setBounds(200, 200, 300, 300);
        setTitle("Mustard's Frame");
        setLayout(new GridLayout(5,1));

        lblFname = new JLabel("First Name");
        txtFname = new JTextField(10);
        panel1 = new JPanel();
        panel1.add(lblFname); panel1.add(txtFname);

        lblbSname = new JLabel("Surname");
        txtSname = new JTextField(10);
        panel12 = new JPanel();
        panel12.add(lblbSname); panel12.add(txtSname);

        lblRegNo = new JLabel("Registration Number");
        txtRegNo = new JTextField(10);
        panel3 = new JPanel();
        panel3.add(lblRegNo); panel3.add(txtRegNo);

        lblPos = new JLabel("program of study");
        txtPos = new JTextField(10);
        panel4 = new JPanel();
        panel4.add(lblPos); panel4.add(txtPos);

        btnsubmit = new JButton("SUBMIT");
        panel5 = new JPanel();
        panel5.add(btnsubmit);

        add(panel1); add(panel12);
        add(panel3); add(panel4);
        add(panel5);

    }

    public void actionListeners(){

        btnsubmit.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e)  {

                try {
                    fileStoring();
                }catch (Exception exc){

                }

                clearFields();
            }
        });
    }

    public void fileStoring() throws Exception{

        System.setOut(ps);

        System.out.printf("%-10s %-15s %-15s %-15s %-15s\n", "Sno.", "First Name", "Surname", "Reg.No", "Program of Study");
        System.out.printf("%-10d %-15s %-15s %-15s %-15s\n",i,txtFname.getText(), txtSname.getText(), txtRegNo.getText(), txtPos.getText()  );
        i++;
        fw.close();
        ps.close();
    }

    public void clearFields(){
        txtFname.setText("");
        txtSname.setText("");
        txtRegNo.setText("");
        txtPos.setText("");

        txtFname.requestFocus();
    }

    public static  void  main(String[] args) throws Exception{
        StudentAssignment obj = new StudentAssignment();
    }

}

标签： java

解决方案

像这样改变你的方法，

public void fileStoring() throws Exception {
        try (FileWriter fileWriter = new FileWriter("C:\\data\\Mustard.txt", true);
                PrintWriter printWriter = new PrintWriter(fileWriter)) {
            if (i == 1) {
                printWriter.printf("%-10s %-15s %-15s %-15s %-15s\n", "Sno.", "First Name", "Surname", "Reg.No",
                        "Program of Study");
            }
            printWriter.printf("%-10d %-15s %-15s %-15s %-15s\n", i, txtFname.getText(), txtSname.getText(),
                    txtRegNo.getText(), txtPos.getText()).toString();
        } catch (IOException e) {
            // handle the exception here.
        }

        i++;
    }

为什么你没有得到想要的结果是你在构造函数中初始化流，然后在第一次写入后关闭流。

fw.close();
ps.close();

然后随后的写入将失败。为了抵消这种情况，您需要在每次写入文件时创建一个新流（即在此方法本身内部，而不是在构造函数内部），然后关闭它。另请注意，您只需要在开始时编写标题，并且您的实现也无法处理。

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