Question

我是编程新手。我正在尝试制作一个软件。但我有问题。

问题是：我的软件是学校管理。因此，当我在java中输入学生卷号时，我需要检索我存储在mysql中的信息（名称，年龄等）。但是我输入的代码总是为我输入的任何滚动提供相同的信息。请帮忙

String LibraryCardNo = txtCard.getText();
    String firstName = "";
    String lastName = "";
    String Job = "";
    String Age = "";
    String LibraryCard = "";

    try{
    Class.forName("java.sql.Driver");
    Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3307/library?" + "user=root&password=ainkhalid"); 

    Statement s = con.createStatement();
    String query = "select * from application";
    ResultSet rs = s.executeQuery(query);

    while(rs.next()){
        firstName = rs.getString("firstName");
        lastName = rs.getString("lastName");
        Job = rs.getString("job");
        Age = rs.getString("age");
        LibraryCard = rs.getString("LibraryCardNo");
    }

    rs.close();
    s.close();
    con.close();
    }

    catch(Exception e){
        String msg = e.getMessage();  
System.out.println("The problem is :"+msg); 
    }

    txtLast.setText(lastName);
    txtFirst.setText(firstName);
    txtJob.setText(Job);
    txtAge.setText(Age);

Answer 1

那是因为你循环结果，但只保留对最后一个的引用

while(rs.next()){
    firstName = rs.getString("firstName");
    lastName = rs.getString("lastName");
    Job = rs.getString("job");
    Age = rs.getString("age");
    LibraryCard = rs.getString("LibraryCardNo");
}

方法ResultSet#next()返回true并移动其内部迭代器，只要还有要读取的数据。

立即尝试打印它们或将所有数据封装到一个类中，实例化对象并将它们添加到列表中，然后打印出来。

public class Student {
    String firstName = "";
    String lastName = "";
    String job = "";
    String age = "";
    String libraryCard = "";

    // getters, setters, and constructors
}

然后

List<Student> students = new LinkedList<>();
while(rs.next()){
    firstName = rs.getString("firstName");
    lastName = rs.getString("lastName");
    Job = rs.getString("job");
    Age = rs.getString("age");
    LibraryCard = rs.getString("LibraryCardNo");
    Student student = new Student(firstName, lastName, Job, Age, LibraryCard);
    students.add(student);
}
// display them accordingly

考虑阅读this official tutorial。

显然，如果您只想从数据库中检索一行，则必须切换查询。像

这样的东西

    String query = "select * from application where roll = ?";

使用PreparedStatement并设置?占位符的值。

用java从mysql中获取数据

1 个答案: