Jsp学习——servlet详解
2011-08-20 23:07
369 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 plaincopy to clipboardprint?
<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>
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 plaincopy to clipboardprint?
<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>
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 plaincopy to clipboardprint?
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);
error.jsp页面代码如下：
view plaincopy to clipboardprint?
login failed!
view plaincopy to clipboardprint?
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();
}
}
}
}
view plaincopy to clipboardprint?
<?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 plaincopy to clipboardprint?
<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>
view plaincopy to clipboardprint? <form action = "login" id = "login" method = "post"> <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 plaincopy to clipboardprint?
<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>
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 plaincopy to clipboardprint? <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> <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 plaincopy to clipboardprint?
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);
view plaincopy to clipboardprint? <%@ 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> <%@ 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 plaincopy to clipboardprint?
login failed!
view plaincopy to clipboardprint? login successful! login successful!LoginServlet类代码如下：
view plaincopy to clipboardprint?
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();
}
}
}
}
view plaincopy to clipboardprint? 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); } } 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 plaincopy to clipboardprint?
<?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>
内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理 
相关文章推荐
- jsp学习之 Context init 参数和servlet init 参数详解
- 【S2HS学习笔记】第二章节：JSP/Servlet及相关技术详解
- Jsp学习——servlet详解
- Jsp学习——servlet详解
- JSP&&SERVLET学习笔记（四）：关于HttpServletRequest
- Servlet学习之web服务器Tomcat 详解
- 【学习笔记】第一章：Java服务端编程15、Servlet概念详解
- JSP、Servlet、JDBC学习笔记
- [读书笔记]JSP-Servlet学习笔记-JDBC
- Servlet与JSP学习笔记（二） Servlet核心
- 学习笔记-----JSP+Servlet+Bean的MVC
- Jsp/Servlet基础-JSP脚本中的8个内置对象详解
- JSP学习笔记（5）-Java Servlet
- Servlet学习笔记（七）：Session详解
- Spring Boot学习4：web篇（下）-Spring boot （Servlet，Jsp）学习
- JSP学习之------>HTTP协议详解
- Servlet与Jsp学习笔记--3、Cookie & jsp
- JSP学习笔记之三——关于servlet配置web.xml出现的问题
- JSP Servlet学习笔记——使用fileupload上传文件
- 学习日志4.16--servlet_JSP