使用java从mysql获取数据

Question

我是编程新手。我正在试着做一个软件。但我有个问题。

问题是:我的软件是学校管理软件。因此，当我在java中输入学生学号时，我需要检索他的信息(姓名、年龄等)，这些信息我存储在mysql中。但我输入的代码总是给出相同的信息，无论我输入的是哪种卷轴。请帮帮忙

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

这是因为您循环遍历结果，但只保留对最后一个结果的引用

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

只要还有数据要读，方法ResultSet#next()就会返回true并移动其内部迭代器。

尝试立即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。就像这样

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

使用PreparedStatement并设置?占位符的值。