用java从mysql中获取数据答案

【问题标题】：Taking data from mysql with java用java从mysql中获取数据
【发布时间】：2013-09-27 19:15:37
【问题描述】：

我是编程新手。我正在尝试制作一个软件。但是我有问题。

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 中的他的信息（姓名、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);

【问题讨论】：

"select * from application" 应该类似于："select * from application where rollNumber = 787878";

标签： java mysql

【解决方案1】：

那是因为你在循环遍历结果，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，只要还有数据要读取就移动它的内部迭代器。

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，然后将其打印出来。

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。类似的东西

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

使用PreparedStatement 并为? 占位符设置值。

【讨论】：