Javabean的理解（通过javabean的部分程序）

1.javabean是一种规范

2.在servlet中我们都会接触数据库，需要将连接数据库的那段代码复制粘贴修改，放入我们写的servlet程序中。如果我们有100个servlet，需要复制粘贴修改100次，那样就显得没有意义了，所以这时候的javabean的含义是一个数据库连接类，让我们调用。

3.如未有javabean的代码

 1 import java.sql.Connection;
 2 import java.sql.DriverManager;
 3 import java.sql.SQLException;
 4 import java.util.Properties;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServlet;import java.io.IOException;
 7 import java.io.*;
 8 import javax.servlet.http.HttpServletRequest;
 9 import javax.servlet.http.HttpServletResponse;
10 public class ServletMysql extends HttpServlet {
11 
12  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException{
13     
14     try {
15             // The newInstance() call is a work around for some
16             // broken Java implementations
17 
18             Class.forName("com.mysql.jdbc.Driver").newInstance();
19              System.out.println("heo");
20             Connection conn = 
21        DriverManager.getConnection("jdbc:mysql://localhost/test?" + 
22                                    "user=root&password=root");
23 
24 
25        
26      
27      
28      
29      System.out.println(conn);
30       PrintWriter out =resp.getWriter();
31       out.println("<html><head><head/><body><h1>hello<h1><body/><html/>");
32       out.flush();
33       out.close();
34               
35         } catch (Exception ex) {
36             // handle the error
37         }
38 
39 
40 
41 
42 
43 
44     
45 }

4.将连接数据库的代码和相关引入的包抽取出来新建立一个类

 1 import java.sql.Connection;
 2 import java.sql.DriverManager;
 3 import java.sql.SQLException;
 4 import java.util.Properties;
 5 
 6 public class JavaBean {
 7     public static Connection getcon() {
 8         Connection conn =null;
 9 
10         try {
11           
12 
13             Class.forName("com.mysql.jdbc.Driver").newInstance();
14              System.out.println("heo");
15              conn = 
16        DriverManager.getConnection("jdbc:mysql://localhost/test?" + 
17                                    "user=root&password=root");
18 
19 
20        
21         
22               
23         } catch (Exception ex) {
24           ex.printStackTrace();
25           
26             
27               
28         }
29 
30           return conn;
31 }
32 }

5.将servlet中的代码用到该类

 1 import javax.servlet.http.HttpServlet;
 2 import javax.servlet.http.HttpServlet;
 3 import java.io.IOException;
 4 import java.io.*;
 5 import javax.servlet.http.HttpServletRequest;
 6 import javax.servlet.http.HttpServletResponse;
 7 
 8 
 9 import java.sql.Connection;
10 import java.sql.DriverManager;
11 import java.sql.SQLException;
12 import java.util.Properties;
13 class httpservlet extends HttpServlet {
14 
15  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException{
16     
17     
18     Connection conn = JavaBean.getcon();
19     System.out.println(conn);
20 
21 
22 
23     PrintWriter out =resp.getWriter();
24     out.println("<html><head><head/><body><h1>hello<h1><body/><html/>");
25     out.flush();
26     out.close();
27 }
28   
29 
30 
31 
32 
33 
34 }

6.将编译好的两个class部署到tomcat项目中去，然后在浏览器端输入资源访问网址

7.可以看到效果，跟未用javabean的结果一样，但是代码量多的话，就不用复制那么多代码了。