Jsp学习——filter的使用
2011-12-21 02:15
417 查看
一、servlet的生命周期
在《JSP学习 —— 开篇:JSP,servlet容器,Tomcat,servlet容器之间的关系》一文中,我已经对servlet的生命周期进行了简单阐述,现在,就来进行详细阐述:servlet其实就是一个Java类,它负责响应和处理页面消息。它的实例化方式有两种:一种是当web应用启动一开始,tomcat就对servlet进行初始化;另一种是当客户端请求一个servlet时,对应的servlet进行创建;创建时调用HttpServlet的Init(或用户自己重写的Init)函数进行初始化,之后调用service函数进行消息响应,最后调用destory方法进行收尾处理。对于其何时创建,如何创建,都不是由我们来控制的,而是由容器根据配置文件自己进行创建。
事实上,在标准MVC结构中,servlet只充当Control部分,它从来不对页面进行输出处理,也不进行业务逻辑处理,只是将页面消息进行对应的后台处理后(期间会和Model打交道),进行简单的页面跳转。
对于servlet类的配置,其实只要注意两点就足够了:一是指定servlet类名,二是指定该类要处理的动作。
view plain
<pre name="code" class="html"> <servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
对于sevlet的名字,暂时我们可以随意指定,对于只有一个servlet类的Web应用而言,是没必要注意的。
要注意而且需要特别注意的时servlet-class和url-pattern,servlet-class指定servlet的类名,类名必须包含完整的包前缀,而url指定要处理的动作名,如:我在这里打算处理一个表单请求的action,
view plain
<form action = "login" id = "login" method = "post">
要处理的action必须和url-pattern相同,否则servlet不能处理我们提交的请求,运行时会出错。
二、load-on-startup Servlet
一般来说,容器会将绝大多数servlet类的初始化都将在页面进行请求之后,然后根据请求找到对应的servlet再初始化,那么如果我们想将一个servlet类在WEB应用启动后尽早的执行初始化,那么只有靠load-on-startup配置参数了。这个配置参数同servlet的配置参数一起配置,它的参数值是个整型值,赋给它的值越小,它就越先初始化。
view plain
<servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
三、访问servlet的配置参数
我们在配置servlet时,还可以配置一些运行时用到的参数,这种参数可以通过ServletConfig类来解析,看起来和我前面讲到的《JSP学习——JSP基础知识(二)
view plain
<servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
<init-param>
<param-name>driver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
<init-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/test_db</param-value>
</init-param>
<init-param>
<param-name>user</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>pass</param-name>
<param-value>900622</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
在需要用到这些参数的servlet类中,我们可以通过ServletConfig对象来解析:
view plain
ServletConfig config = getServletConfig();
String driver = config.getInitParameter("driver");
String url = config.getInitParameter("url");
String user = config.getInitParameter("user");
String pass = config.getInitParameter("pass");
DbDao dao = DbDao.instance(driver,url,user,pass);
四、综合应用:servlet作为MVC架构中Control层的实例——一个简单的登录验证
index.jsp页面代码如下:
view plain
<%@ page language="java" import="java.util.*" errorPage="error.jsp"%>
<%@ page pageEncoding="gb2312"%>
<%@page import="java.sql.SQLException"%>
<%@page import="java.net.ConnectException"%>
<%@page import="java.sql.DriverManager"%>
<%@page import="java.sql.*" %>
<html>
<body>
<form action = "login" id = "login" method = "post">
user name:<input type = "text" name = "username"><hr>
user password:<input type = "text" name = "userpassword"><hr>
<input type = "submit" value = "submit"><br>
</form>
</body>
</html>
error.jsp页面代码如下:
view plain
login failed!
success.jsp页面代码如下:
view plain
login successful!
LoginServlet类代码如下:
view plain
package com.cancique.dao;
import java.io.IOException;
import java.sql.*;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class LoginServlet extends HttpServlet{
public void service(HttpServletRequest request,
HttpServletResponse response)
{
RequestDispatcher rd; //请求转发
String username = request.getParameter("username");
String userpassword = request.getParameter("userpassword");
String errMsg = null;
try
{
ServletConfig config = getServletConfig();
String driver = config.getInitParameter("driver");
String url = config.getInitParameter("url");
String user = config.getInitParameter("user");
String pass = config.getInitParameter("pass");
DbDao dao = DbDao.instance(driver,url,user,pass);
String sql = "select userpassword from user_information where username = '" + username + "'";
ResultSet resultSet = dao.query(sql);
if(resultSet.next())
{
if(resultSet.getString("userpassword").equals(userpassword))
{
HttpSession session = request.getSession(true);
session.setAttribute("username", username);
rd = request.getRequestDispatcher("/success.jsp");
rd.forward(request, response);
}
else
{
errMsg +="密码错误!";
}
}
else
{
errMsg += "用户名错误!";
}
}catch(Exception e)
{
rd = request.getRequestDispatcher("/error.jsp");
request.setAttribute("exception", "业务异常");
try {
rd.forward(request, response);
} catch (ServletException e1) {
e1.printStackTrace();
} catch (IOException e1) {
e1.printStackTrace();
}
}
}
}
DbDao类代码如下(使用Singleton设计模式):
view plain
package com.cancique.dao;
import java.sql.*;
public class DbDao {
private static DbDao dao;
private Connection conn;
private String driver;
private String url;
private String username;
private String pass;
private DbDao()
{}
private DbDao(String driver,String url,
String username,String pass)
{
this.driver = driver;
this.url = url;
this.username = username;
this.pass = pass;
}
public static DbDao getDao() {
return dao;
}
public static void setDao(DbDao dao) {
DbDao.dao = dao;
}
public String getDriver() {
return driver;
}
public void setDriver(String driver) {
this.driver = driver;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPass() {
return pass;
}
public void setPass(String pass) {
this.pass = pass;
}
public void getConnection() throws ClassNotFoundException, SQLException
{
if(conn == null)
{
Class.forName(this.driver);
conn = DriverManager.getConnection(url, username, pass);
}
}
public static DbDao instance(String driver,String url,
String username,String pass)
{
if(dao == null)
{
dao = new DbDao(driver,url,username,pass);
}
return dao;
}
public boolean insert(String sql) throws ClassNotFoundException, SQLException
{
getConnection();
Statement statement = conn.createStatement();
if(statement.executeUpdate(sql) != -1)
{
return false;
}
return true;
}
public ResultSet query(String sql) throws ClassNotFoundException, SQLException
{
getConnection();
Statement statement = conn.createStatement();
return statement.executeQuery(sql);
}
public void delete(String sql) throws ClassNotFoundException, SQLException
{
getConnection();
Statement statement = conn.createStatement();
statement.executeUpdate(sql);
}
public void update(String sql) throws ClassNotFoundException, SQLException
{
getConnection();
Statement statement = conn.createStatement();
statement.executeUpdate(sql);
}
}
web.xml配置文件信息如下:
view plain
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
<init-param>
<param-name>driver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
<init-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/test_db</param-value>
</init-param>
<init-param>
<param-name>user</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>pass</param-name>
<param-value>900622</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
</web-app>
在《JSP学习 —— 开篇:JSP,servlet容器,Tomcat,servlet容器之间的关系》一文中,我已经对servlet的生命周期进行了简单阐述,现在,就来进行详细阐述:servlet其实就是一个Java类,它负责响应和处理页面消息。它的实例化方式有两种:一种是当web应用启动一开始,tomcat就对servlet进行初始化;另一种是当客户端请求一个servlet时,对应的servlet进行创建;创建时调用HttpServlet的Init(或用户自己重写的Init)函数进行初始化,之后调用service函数进行消息响应,最后调用destory方法进行收尾处理。对于其何时创建,如何创建,都不是由我们来控制的,而是由容器根据配置文件自己进行创建。
事实上,在标准MVC结构中,servlet只充当Control部分,它从来不对页面进行输出处理,也不进行业务逻辑处理,只是将页面消息进行对应的后台处理后(期间会和Model打交道),进行简单的页面跳转。
对于servlet类的配置,其实只要注意两点就足够了:一是指定servlet类名,二是指定该类要处理的动作。
view plain
<pre name="code" class="html"> <servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
对于sevlet的名字,暂时我们可以随意指定,对于只有一个servlet类的Web应用而言,是没必要注意的。
要注意而且需要特别注意的时servlet-class和url-pattern,servlet-class指定servlet的类名,类名必须包含完整的包前缀,而url指定要处理的动作名,如:我在这里打算处理一个表单请求的action,
view plain
<form action = "login" id = "login" method = "post">
要处理的action必须和url-pattern相同,否则servlet不能处理我们提交的请求,运行时会出错。
二、load-on-startup Servlet
一般来说,容器会将绝大多数servlet类的初始化都将在页面进行请求之后,然后根据请求找到对应的servlet再初始化,那么如果我们想将一个servlet类在WEB应用启动后尽早的执行初始化,那么只有靠load-on-startup配置参数了。这个配置参数同servlet的配置参数一起配置,它的参数值是个整型值,赋给它的值越小,它就越先初始化。
view plain
<servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
三、访问servlet的配置参数
我们在配置servlet时,还可以配置一些运行时用到的参数,这种参数可以通过ServletConfig类来解析,看起来和我前面讲到的《JSP学习——JSP基础知识(二)
》里面提到的application对象解析配置文件中数据库连接信息的参数很类似,不同的是application可以在任何地方进行解析,而ServletConfig对象只能在servlet中进行解析。比如:如果我们在servlet中需要得到数据库的连接信息以初始化DAO对象,那么可以在web.xml的servlet配置信息中增加一些配置参数:
view plain
<servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
<init-param>
<param-name>driver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
<init-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/test_db</param-value>
</init-param>
<init-param>
<param-name>user</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>pass</param-name>
<param-value>900622</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
在需要用到这些参数的servlet类中,我们可以通过ServletConfig对象来解析:
view plain
ServletConfig config = getServletConfig();
String driver = config.getInitParameter("driver");
String url = config.getInitParameter("url");
String user = config.getInitParameter("user");
String pass = config.getInitParameter("pass");
DbDao dao = DbDao.instance(driver,url,user,pass);
四、综合应用:servlet作为MVC架构中Control层的实例——一个简单的登录验证
index.jsp页面代码如下:
view plain
<%@ page language="java" import="java.util.*" errorPage="error.jsp"%>
<%@ page pageEncoding="gb2312"%>
<%@page import="java.sql.SQLException"%>
<%@page import="java.net.ConnectException"%>
<%@page import="java.sql.DriverManager"%>
<%@page import="java.sql.*" %>
<html>
<body>
<form action = "login" id = "login" method = "post">
user name:<input type = "text" name = "username"><hr>
user password:<input type = "text" name = "userpassword"><hr>
<input type = "submit" value = "submit"><br>
</form>
</body>
</html>
error.jsp页面代码如下:
view plain
login failed!
success.jsp页面代码如下:
view plain
login successful!
LoginServlet类代码如下:
view plain
package com.cancique.dao;
import java.io.IOException;
import java.sql.*;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class LoginServlet extends HttpServlet{
public void service(HttpServletRequest request,
HttpServletResponse response)
{
RequestDispatcher rd; //请求转发
String username = request.getParameter("username");
String userpassword = request.getParameter("userpassword");
String errMsg = null;
try
{
ServletConfig config = getServletConfig();
String driver = config.getInitParameter("driver");
String url = config.getInitParameter("url");
String user = config.getInitParameter("user");
String pass = config.getInitParameter("pass");
DbDao dao = DbDao.instance(driver,url,user,pass);
String sql = "select userpassword from user_information where username = '" + username + "'";
ResultSet resultSet = dao.query(sql);
if(resultSet.next())
{
if(resultSet.getString("userpassword").equals(userpassword))
{
HttpSession session = request.getSession(true);
session.setAttribute("username", username);
rd = request.getRequestDispatcher("/success.jsp");
rd.forward(request, response);
}
else
{
errMsg +="密码错误!";
}
}
else
{
errMsg += "用户名错误!";
}
}catch(Exception e)
{
rd = request.getRequestDispatcher("/error.jsp");
request.setAttribute("exception", "业务异常");
try {
rd.forward(request, response);
} catch (ServletException e1) {
e1.printStackTrace();
} catch (IOException e1) {
e1.printStackTrace();
}
}
}
}
DbDao类代码如下(使用Singleton设计模式):
view plain
package com.cancique.dao;
import java.sql.*;
public class DbDao {
private static DbDao dao;
private Connection conn;
private String driver;
private String url;
private String username;
private String pass;
private DbDao()
{}
private DbDao(String driver,String url,
String username,String pass)
{
this.driver = driver;
this.url = url;
this.username = username;
this.pass = pass;
}
public static DbDao getDao() {
return dao;
}
public static void setDao(DbDao dao) {
DbDao.dao = dao;
}
public String getDriver() {
return driver;
}
public void setDriver(String driver) {
this.driver = driver;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPass() {
return pass;
}
public void setPass(String pass) {
this.pass = pass;
}
public void getConnection() throws ClassNotFoundException, SQLException
{
if(conn == null)
{
Class.forName(this.driver);
conn = DriverManager.getConnection(url, username, pass);
}
}
public static DbDao instance(String driver,String url,
String username,String pass)
{
if(dao == null)
{
dao = new DbDao(driver,url,username,pass);
}
return dao;
}
public boolean insert(String sql) throws ClassNotFoundException, SQLException
{
getConnection();
Statement statement = conn.createStatement();
if(statement.executeUpdate(sql) != -1)
{
return false;
}
return true;
}
public ResultSet query(String sql) throws ClassNotFoundException, SQLException
{
getConnection();
Statement statement = conn.createStatement();
return statement.executeQuery(sql);
}
public void delete(String sql) throws ClassNotFoundException, SQLException
{
getConnection();
Statement statement = conn.createStatement();
statement.executeUpdate(sql);
}
public void update(String sql) throws ClassNotFoundException, SQLException
{
getConnection();
Statement statement = conn.createStatement();
statement.executeUpdate(sql);
}
}
web.xml配置文件信息如下:
view plain
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>myServlet</servlet-name>
<servlet-class>com.cancique.dao.LoginServlet</servlet-class>
<init-param>
<param-name>driver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
<init-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/test_db</param-value>
</init-param>
<init-param>
<param-name>user</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>pass</param-name>
<param-value>900622</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>myServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
</web-app>
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