環境：eclipse，mysql

1. 在mysql裡面建表test

2. 匯入連結mysql的jar包

3. 建立DataAccess的工具類，在這個類裡面執行資料庫連結操作，返回Connection這個物件。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

/**
 *  test 資料庫連線操作
 * @author Administrator
 *
/
  public class DataAccess {
  private static final String driver="com.mysql.jdbc.Driver";
  private static final String url="jdbc:mysql://localhost:3306/test
                       ?useUnicode=true&characterEncoding=UTF-8&useSSL=true";
  private static final String username="root";
  private static final String passwork="2315806986";
  private   static Connection   conn=null; 

 static{
     try{
         //載入驅動
         Class.forName(driver);
     }catch(Exception ex){
         ex.printStackTrace();
     }
 }

 public static Connection getConnection()   throws Exception{
     if(conn==null){
         //連線資料庫
         conn=DriverManager.getConnection(url, username, passwork);
         return conn;
     }

     //判斷資料庫連線是否成功
     if(conn!=null){
         System.out.println("連線正常");
     }else{
         System.out.println("連線異常");
     }

     return conn;
 }

 public static Boolean closeConnection(){
     if(conn != null){
         try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
     }
    return true;
 }
 

}

4. User的實體類，test資料庫裡面的test表有關欄位組成這個類，便於對資料進行操作

public class User {
private int id;
private String name;
private int age;

public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public int getAge() {
    return age;
}
public void setAge(int age) {
    this.age = age;
}
 

}

5. 查詢的操作類，裡面包括一個quaryAll（）的函式，查詢資料庫test表的所有資料，返回ArrayList < User > ；

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;

public class UserDAO {

/**
        * 查詢資料庫裡面所有的資料
        * @return
     */
        public static ArrayList<User> quaryAll(){
    Connection conn = null;
    PreparedStatement stmt = null;
    ResultSet rs = null;
    ArrayList<User> list = new ArrayList<User>();

    try {
        conn = DataAccess.getConnection();
        String sql = "select * from test;";
        stmt = conn.prepareStatement(sql);
        rs = stmt.executeQuery();
        while (rs.next()) {
            User item = new User();
            item.setAge(rs.getInt("age"));
            item.setName(rs.getString("name"));
            item.setId(rs.getInt("id"));
            list.add(item);
        }

        return list;
    } catch (Exception ex) {
        ex.printStackTrace();
        return null;
    } finally {
        if (rs != null) {
            try {
                rs.close();
                rs = null;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
                stmt = null;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }
}
}
 

6. 測試的test類，主函式，打印出所查資料。

import java.util.ArrayList;

public class Test {

public static void main(String[] args) {
    ArrayList<User> userList = UserDAO.quaryAll();
    for(User user : userList){
        System.out.println("查詢出來的id是："+user.getId());
        System.out.println("查詢出來的名字是："+user.getName());
        System.out.println("查詢出來的年齡是："+user.getAge());
    }
}

}

7.執行結果