对于servlet初步理解
程序员文章站
2022-03-24 23:45:52
servlet在mvc框架中经常担当控制器(controller)的角色,其作用类似于调度员,下面我们就根据一个简单javaee的示例来理解servlet的机制和原理.
树结构如上,其中...
servlet在mvc框架中经常担当控制器(controller)的角色,其作用类似于调度员,下面我们就根据一个简单javaee的示例来理解servlet的机制和原理.
树结构如上,其中
login.jsp作为测试用户登录页面.
welcome.jsp作为登录成功页面
dadao.java作为数据库操作类
loginservlet.java就是我们所说的servlet类
我们来看具体内容:
login.jsp
<%@ page language="java" contenttype="text/html; charset=utf-8"
pageencoding="utf-8"%>
<!doctype html public "-//w3c//dtd html 4.01 transitional//en" "https://www.w3.org/tr/html4/loose.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; utf-8">
<title>连接数据库范例</title>
</head>
<body>
<span style="color: blue; font-weight: bold;"> <%
if (request.getattribute("err") != null) {
out.println(request.getattribute("err") + "<br/>");
}
%>
</span> 请输入用户名密码:
<form id="login" method="post" action="login">
用户名: <input type="text" name="username"><br /> 密码:<input
type="password" name="password"><br /> <input type="submit"
value="登录"><br />
</form>
</body>
</html>
以上页面只负责传递两个参数,一个是用户名,另一个是用户密码,将参数传递给loginservlet的实例中,再通过验证数据库进行结果判断,然后servlet将结果视图反馈给用户.
welcome.
<%@ page contenttype="text/html; charset=gbk" language="java" errorpage="" %>
欢迎登录
<%=session.getattribute("name")%>,欢迎登录！
此页面是用户密码验证成功后返回的视图.
dbdao.java
package glq;
import java.sql.connection;
import java.sql.drivermanager;
import java.sql.preparedstatement;
import java.sql.resultset;
public class dbdao {
private connection conn;
private string driver;
private string url;
private string username;
private string password;
public dbdao() {
}
public dbdao(string driver, string url, string username, string password) {
this.driver = driver;
this.url = url;
this.username = username;
this.password = password;
}
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 getpassword() {
return password;
}
public void setpassword(string password) {
this.password = password;
}
public connection getconnection() throws exception {
if(conn==null){
class.forname(this.driver);
conn=drivermanager.getconnection(url, username, password);
}
return conn;
}
public boolean insert(string sql,object... args) throws exception, throwable{
preparedstatement ps=getconnection().preparestatement(sql);
for(int i=0;i
loginservlet.java
package glq;
import java.io.ioexception;
import java.sql.resultset;
import javax.servlet.requestdispatcher;
import javax.servlet.servletexception;
import javax.servlet.annotation.webservlet;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import javax.servlet.http.httpsession;
@webservlet(name="login" ,urlpatterns={"/login"})
public class loginservlet extends httpservlet {
/**
*
*/
private static final long serialversionuid = 1l;
@override
protected void service(httpservletrequest req, httpservletresponse res) throws servletexception, ioexception {
string errmsg = "";
requestdispatcher rd;
string username = req.getparameter("username");
string password = req.getparameter("password");
try {
//创建数据库构造函数
//注意,连接时要在数据库中创建名为servlet的数据库
dbdao dd = new dbdao("com.mysql.jdbc.driver", "jdbc:mysql://localhost:3306/servlet", "root", "123456");
//执行查询方法
//注意,要在servlet数据库中添加user_inf表,并在表中添加两个属//性:name,pass
resultset rs = dd.query("select pass from user_inf where name=?", username);
//如果存在该用户
if (rs.next()) {
//判定用户密码是否相同
if (rs.getstring("pass").equals(password)) {
//获得session
httpsession session = req.getsession();
//注册name值为username
session.setattribute("name", username);
//将参数和页面转向welcome.jsp
rd = req.getrequestdispatcher("/welcome.jsp");
rd.forward(req, res);
} else {
//如果密码匹配失败
errmsg += "密码不对,请重新输入";
}
} else {
//如果没找到用户
errmsg += "用户不存在";
}
} catch (exception e) {
e.printstacktrace();
}
//当错误信息存在时,将错误信息errmsg作为参数传递给request中的err变//量,使其在登录页面显示,并因为登录失败跳转至登录页面
if (errmsg != null && !errmsg.equals("")) {
rd = req.getrequestdispatcher("/login.jsp");
req.setattribute("err", errmsg);
rd.forward(req, res);
}
}
}
在测试时,需要在web-inf的lib文件中加入mysql-connector-java-5.1.38-bin.jar包,此包为数据库工具包.
至于tomcat的构建,以及web项目的建立,需要自行检索.