JavaBean组件-数据库+JavaBean（四）-蒲公英云

JavaBean组件-数据库+JavaBean（四）

桃扇骨 2021-10-01 05:56 490阅读 0赞

封装了一个数据库的类DBAccess.java

package mb.dao;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class DBAccess {
//    数据库连接
    private Connection conn = null;
//    sql语句执行容器
    private Statement stmt = null;
//    查询结果集
    private ResultSet rs = null;
//    预定义sql语句执行容器
    private PreparedStatement pstmt = null;
    public DBAccess() {
    }
    /** 数据库连接方法，获得Connection对象 **/
    public Connection getConn() {
        if (conn == null) {
            getConnection();
        }
        return conn;
    }
    /** 数据库连接方法,获得Statement对象 **/
    public void getConnection() {
        try {
//             显式地加载JDBC本地API驱动程序
            Class.forName("com.mysql.jdbc.Driver")
                    .newInstance(); 
//            olLearn为数据库名称
            String url = "jdbc:mysql://localhost:3306/ollearn?useUnicode=true&characterEncoding=utf-8";
            String user = "root";
            String pwd = "123";
//             创建Connection对象con
            this.conn = DriverManager.getConnection(url, user, pwd); 
//            根据conn对象创建sql语句执行容器对象stmt
            this.stmt = this.conn.createStatement();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    /** 数据库查询方法,获得ResultSet对象 **/
    public ResultSet query(String strSql) {
        ResultSet rs = null;
        try {
//            这个是没预编译sql语句的查询
            rs = stmt.executeQuery(strSql);        
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return rs;
    }
    /** 数据库查询方法,利用查询预处理对象，获得ResultSet对象 **/
    public ResultSet query(PreparedStatement pstmt) {
        this.pstmt = pstmt;
        ResultSet rs = null;
        try {
            rs = this.pstmt.executeQuery();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return rs;
    }
    /** 关闭连接 **/
    public void closeConnection() {
        try {
            if (rs != null) {
                rs.close();
                rs = null;
            }
            if (stmt != null) {
                stmt.close();
                stmt = null;
            }
            if (conn != null) {
                conn.close();
                conn = null;
            }
            if (pstmt != null) {
                pstmt.close();
                pstmt = null;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

jsp中：

<jsp:useBean id="term" class="mb.service.termService" scope="page" />
<jsp:getProperty name="term" property="currTerm"/>

业务处理类termService.java

package mb.service;
import java.sql.ResultSet;
import mb.dao.DBAccess;
public class termService {
    public termService() {
    }
    public String getCurrTerm()
    {
        String sCurrTerm = "";
        DBAccess dba=new DBAccess();
        try{
            if(dba.getConn()!=null){
                String sSql="select * from term where iFlag=1";        
                ResultSet rs=dba.query(sSql);
                while(rs!=null&&rs.next()){
                    if(rs.getString("sTname")!=null){
                        sCurrTerm = rs.getString("sTname");
                    }                        
                }
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally{
            dba.closeConnection();
        }
        return sCurrTerm;
    }
}