Java通过JDBC连接MySQL数据库

代码描述：把前台获取的字段作为查询条件，返回符合条件的记录。

package com.imooc.dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import com.imooc.bean.Message;

/**
 * 处理与数据库相关的查询操作
 *
 */
public class MessageDao {
    public List<Message> queryMessageList(String command,String description){
        List<Message> messageList = new ArrayList<Message>();
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/micro_message", "root", "admin");
            // StringBuilder速度快适合单线程，StringBuffer适合多线程操作大量数据，String每次都是生成新对象，需要垃圾回收。
            StringBuilder sb = new StringBuilder("select ID,COMMAND,DESCRIPTION,CONTENT from message where 1=1 ");
            // String sql = "select ID,COMMAND,DESCRIPTION,CONTENT from message";
            List<String> paramList = new ArrayList<String>();
            if(null != command && !"".equals(command)){
                sb.append(" and COMMAND=?");
                paramList.add(command);
            }
            if(null != description && !"".equals(description)){
                // MySQL中用%表示任意字符，用空格用于连接
                sb.append(" and DESCRIPTION like '%' ? '%'");
                paramList.add(description);
            }
            PreparedStatement pstmt = conn.prepareStatement(sb.toString());
            for(int i=0;i<paramList.size();i++){
                // 给PreparedStatement中预执行SQL语句追加值
                pstmt.setString(i+1, paramList.get(i));
            }
            ResultSet rs = pstmt.executeQuery();
            while(rs.next()){
                Message message = new Message();
                messageList.add(message);// 这里messageList是个容器，只是对message的引用，所以可以提前放入容器中
                message.setId(rs.getString("ID"));
                message.setCommand(rs.getString("COMMAND"));
                message.setDescription(rs.getString("DESCRIPTION"));
                message.setContent(rs.getString("CONTENT"));
            }
    }catch (ClassNotFoundException e) {
        e.printStackTrace();
    }catch (SQLException e) {
        e.printStackTrace();
    }
    return messageList;
  }
    
}