java 如何访问java中另一个类中的连接对象？
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how to access connection object in another class in java?
提问by su_darell
i am using xampp mysql, this code is for JDBC program. actually there are two class one is dbconnect.java and another is login.java. I want to access the connection object (i.e. conn) in another class(i.e. login.java). But i don't have proper idea, i have included the code here please suggest me what is the problem and what are the solutions?
我正在使用 xampp mysql，此代码用于 JDBC 程序。实际上有两个类，一个是dbconnect.java，另一个是login.java。我想访问另一个类（即 login.java）中的连接对象（即 conn）。但是我没有正确的想法，我在这里包含了代码，请告诉我问题是什么以及解决方案是什么？
This is the code of dbconnect.java
这是dbconnect.java的代码
package stundentrecord;
import java.sql.Connection;
import java.sql.DriverManager;
public class dbconnect {
public void conect(){
Connection con = null;
String url = "jdbc:mysql://localhost:3306/";
String db = "studentRecord";
String driver = "com.mysql.jdbc.Driver";
String user = "root";
String pass = "";
try{
Class.forName(driver);
con = DriverManager.getConnection(url + db, user, pass);
if(con==null){
System.out.println("Connection cannot be established");
}
// con.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
and here is the code from another class named login.java
这是来自另一个名为 login.java 的类的代码
if(source==login){
if(username!=null && password!=null) {
Connection conn= null;
Statement stmt = null;
dbconnect db = new dbconnect();
db.conect();
String query = "SELECT * from userlogin";
try{
stmt=(Statement) conn.createStatement(); // here is the problem
ResultSet rs = stmt.executeQuery(query); // here is the problem
while (rs.next()) {
String user = rs.getString("username");
String pass=rs.getString("password");
System.out.println("Welcome "+user);
}
} catch(SQLException ex){
ex.getMessage();
}
StundentRecord SR = new StundentRecord();
} else {
JOptionPane.showMessageDialog(null,"Username or password field is empty","error !!",JOptionPane.ERROR_MESSAGE);
}
}
What is the real problem and how to solve it?
真正的问题是什么以及如何解决？
回答by Boris the Spider
The easiest way would be to make the connect method non voidand return the connection:
最简单的方法是使连接方法非void并返回连接：
public Connection conect() {
Connection con = null;
String url = "jdbc:mysql://localhost:3306/";
String db = "studentRecord";
String driver = "com.mysql.jdbc.Driver";
String user = "root";
String pass = "";
try {
Class.forName(driver);
con = DriverManager.getConnection(url + db, user, pass);
if (con == null) {
System.out.println("Connection cannot be established");
}
return con;
} catch (Exception e) {
System.out.println(e);
}
return null;
}
回答by Kanagaraj M
You should return your CONNECTION object from you connection class and assign it to your login class... Now your connection object is null...
您应该从您的连接类返回您的 CONNECTION 对象并将其分配给您的登录类...现在您的连接对象为空...
