前言
在许许多多的B/S架构系统中都涉及到了数据库的链接,那么对于数据库连接的方式有哪些?可能出现的问题是什么?
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目录
1.普通连接方式
2.单例模式
3.连接池
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分析
普通连接:
下面是我们一般使用的普通连接方式的代码(jsp)
package com.jdbc.dao;import java.sql.*;
public class BaseDAO {
//打开数据库链接 public Connection getConn()
{
Connection conn = null;
try {
//加载驱动 Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
//打开链接 conn = DriverManager.getConnection("jdbc:sqlserver://localhost:1433;DatabaseName = epetDB","sa","sa");
� � � � � � � � } catch (ClassNotFoundException e) {
� � � � � � � � � � � � // TODO Auto-generated catch block � � � � � � � � � � � �e.printStackTrace();
� � � � � � � � } catch (SQLException e) {
� � � � � � � � � � � � // TODO Auto-generated catch block � � � � � � � � � � � �e.printStackTrace();
� � � � � � � � }
� � � � � � � � return conn;
� � � � }
� � � � //(重写)关闭链接 � � � �public void Close(Connection conn,PreparedStatement pstmt,ResultSet rs)
� � � � {
� � � � � � � � try {
� � � � � � � � � � � � //关闭结果集 � � � � � � � � � � � �if (rs != null) {
� � � � � � � � � � � � � � � � rs.close();
� � � � � � � � � � � � }
� � � � � � � � � � � � //关闭PerparedStatement对象 � � � � � � � � � � � �if (pstmt != null) {
� � � � � � � � � � � � � � � � pstmt.close();
� � � � � � � � � � � � }
� � � � � � � � � � � � //关闭链接 � � � � � � � � � � � �if (conn != null) {
� � � � � � � � � � � � � � � � conn.close();
� � � � � � � � � � � � }
� � � � � � � � } catch (Exception e) {
� � � � � � � � � � � � // TODO: handle exception � � � � � � � �}
� � � � }
� � � � //(重写)关闭链接 � � � �public void Close(Connection conn,PreparedStatement pstmt)
� � � � {
� � � � � � � � try {
� � � � � � � � � � � � //关闭PerparedStatement对象 � � � � � � � � � � � �if (pstmt != null) {
� � � � � � � � � � � � � � � � pstmt.close();
� � � � � � � � � � � � }
� � � � � � � � � � � � //关闭链接 � � � � � � � � � � � �if (conn != null) {
� � � � � � � � � � � � � � � � conn.close();
� � � � � � � � � � � � }
� � � � � � � � } catch (Exception e) {
� � � � � � � � � � � � // TODO: handle exception � � � � � � � �}
� � � � }
� � � � //增删改操作 � � � �public int Update(String sql,Object[] parm)
� � � � {
� � � � � � � � int iRet = 0;
� � � � � � � � Connection conn = null;
� � � � � � � � PreparedStatement pstmt = null;
� � � � � � � � try {
� � � � � � � � � � � � conn = getConn();
� � � � � � � � � � � � pstmt = conn.prepareStatement(sql);
� � � � � � � � � � � � //循环赋值参数 � � � � � � � � � � � �for (int i = 0; i < parm.length; i++) {
� � � � � � � � � � � � � � � � //为预编译sql设置参数 � � � � � � � � � � � � � � � �pstmt.setObject(i+1, parm);
� � � � � � � � � � � � }
� � � � � � � � � � � � //执行SQL语句 � � � � � � � � � � � �iRet = pstmt.executeUpdate();
� � � � � � � � } catch (Exception e) {
� � � � � � � � � � � � e.printStackTrace();
� � � � � � � � }
� � � � � � � � finally � � � � � � � �{
� � � � � � � � � � � � Close(conn,pstmt);
� � � � � � � � }
� � � � � � � � return iRet;
� � � � }
}
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普及:
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try{//可能出现异常的代码}catch(Execption e){//如果发生异常处理的代码}finally{//无论是否异常都会执行的代码try catch finally java中异常处理机制
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我们来分析一下写一段代码,其中Update方法是用来更新数据的,其中我们可以看到try中包含了getConn()方法用来获取Connection连接对象,到最后我们可以在finally代码块中看到Close()方法用来关闭创建的Connection对象以及PreparedStatement对象,这么消耗我们很大的内存空间。
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如果用户同时点注册按钮那么服务器首先执行打开数据库连接Connection多个用户注册就会打开多个Connection那么并且同时添加到数据库,服务器就会在执行添加的时候就会发生异常。分不清楚用户注册的信息。
举个例子:
左边的三个人同时对另一人喊不同的一个字,右边的一个人就会分不清,左边三个人喊了什么?(可以做真人实例)
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总结:
从分析中,我们看到普通的连接方式中无法处理并发问题!如果你想知道解决方法那么请继续看下去。
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单例连接:
下面一段单利模式中的数据库连接代码
package dao;
�import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;
�public class BaseDao {
� � � � private String className = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
� � � � private String url = "jdbc:sqlserver://localhost:1433;databasename=SQLTMP";
� � � � private String user = "sa";
� � � � private String pwd = "sa";
� � � � private static Connection conn = null;
� � � � �
� � � � private BaseDao(){
� � � � � � � � try {
� � � � � � � � � � � � Class.forName(className);
� � � � � � � � � � � � conn = DriverManager.getConnection(url,user,pwd);
� � � � � � � � } catch (ClassNotFoundException e) {
� � � � � � � � � � � � e.printStackTrace();
� � � � � � � � } catch (SQLException e) {
� � � � � � � � � � � � e.printStackTrace();
� � � � � � � � }
� � � � � � � � �
� � � � }
� � � � �
� � � � public static Connection getConn(){
� � � � � � � � if(conn != null){
� � � � � � � � � � � � return conn;
� � � � � � � � }else{
� � � � � � � � � � � � new BaseDao();
� � � � � � � � � � � � return conn;
� � � � � � � � }
� � � � }
}
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普及:
构造方法:访问修饰符(public|private) 类名
构造方法在实例化的时候就会调用
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我们分析一下这一段代码中Connection在构造方法中创建用过getConn方法获取连接。
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我们从图片中和代码中可以看到全程中只有一个Connection连接,那么这样就可以降低服务器的压力,解决并发问题
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总结:
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从分析中,我们看到单例模式,可以减轻服务器的压力,解决并发问题,如果够仔细的话大家会发现getConn方法是一个静态方法,而且其他属性和方法都是private从而大大提高了安全性。这种连接方式适合:个人开发和国家单位开发(安全性高)
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连接池:
下面一段连接池数据库连接代码
context.xml
� � � � �Web.xml � �news DataSource � �news � �javax.sql.DataSource � �Container � ��
�package com.news.dao;import java.sql.*;
�import javax.naming.*;import javax.sql.DataSource;
�public class BaseDao {
� � � � /** � � � � * 创建连接池
� � � � �* */ � � � �public Connection getConn(){
� � � � � � � � Connection conn = null;
� � � � � � � � try {
� � � � � � � � � � � � Context ctx = new InitialContext();
� � � � � � � � � � � � DataSource ds = (DataSource)ctx.lookup("java:comp/env/news");
� � � � � � � � � � � � conn = ds.getConnection();
� � � � � � � � } catch (NamingException e) {
� � � � � � � � � � � � e.printStackTrace();
� � � � � � � � } catch (SQLException e) {
� � � � � � � � � � � � e.printStackTrace();
� � � � � � � � }
� � � � � � � � return conn;
� � � � }
}
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普及:
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连接池:连接池是创建和管理一个连接的缓冲池的技术,这些连接准备好被任何需要他们的线程使用。
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我们可以直接使用getConn方法获得Connection并且执行数据操作,执行完成之后连接池会回收Connection这样就解决了普通模式中的并发问题.
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总结:
从分析中,我们看到Connection不需要创建,这样就简化编程模式,这样减少了连接的创建时间,连接池能够使性能最大化,同事还能将资源利用控制在一定的水平之下,如果超过该水平,应用程序将崩溃而不仅仅是变慢。
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写在最后
清楚的了解B/S架构中的数据库连接方式,在合适的情况下使用合适的连接方式感觉还是棒棒哒 ~ ~!
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来源:i春秋学院博客园