The explanation of servlet in Baidu is:
A server-side program written in Java. Its main function is to browse and modify data interactively and generate dynamic Web content. A Servlet in a narrow sense refers to an interface implemented by the Java language, and a Servlet in a broad sense refers to any class that implements the Servlet interface. In general, people understand Servlet as the latter.
Learn and understand:
As far as I know, there are many ways to write servlets, and it is more common to integrate the httpservlet class, and then override methods such as doget and dopost. So I base my understanding on this.
This simple implementation needs to import the jar package of the servlet in the project.
To verify that the servlet you wrote and the configuration are correct, you need to involve a simple page, jsp or html, as follows:
- <!DOCTYPE html>
- <html>
- <head>
- <metahttp-equiv="Content-Type"content="text/html; charset=utf-8"/>
- </head>
- <body>
- <formaction="./cookieServlet"method="post">
- <inputtype="text"name="userName"/>
- <inputtype="password"name="password"/>
- <inputtype="submit"value="login"/>
- </form>
- </body>
- </html>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
</head>
<body>
<form action="./cookieServlet" method="post">
<input type="text" name="userName"/>
<input type="password" name="password"/>
<input type="submit" value="login"/>
</form>
</body>
</html>
页面只是个非常简单的form表单，包含了username和password两个文本输入框，和表单提交按钮。需要注意的是，input中不能少了name属性，这个属性是和后台交互的关键，有了它，后台才能用request.
getParameter()方法正确获取文本框中输入的内容。这一点有经验的朋友肯定都知道，但刚进入软件开发的时候我因为不知道这个问题而遇到过困难，想来对初学者大概有用。
在这个页面中，填好用户名和密码后，点击提交，浏览器会向服务器发送一个cookieServlet请求，同时把页面填好的userName和password传入后台。后台就可以通过相应的方法获取数据进行一定的逻辑处理，对应的servlet代码如下：
- package servletTest;
- import java.io.IOException;
- import javax.servlet.ServletException;
- import javax.servlet.http.Cookie;
- import javax.servlet.http.HttpServlet;
- import javax.servlet.http.HttpServletRequest;
- import javax.servlet.http.HttpServletResponse;
- import javax.servlet.http.HttpSession;
- public class CookieServlet extends HttpServlet {
- @Override
- protected void doGet(HttpServletRequest req, HttpServletResponse resp)
- throws ServletException, IOException {
- super.doGet(req, resp);
- }
- @Override
- protected void doPost(HttpServletRequest req, HttpServletResponse resp)
- throws ServletException, IOException {
- String userName = req.getParameter("userName");
- String password = req.getParameter("password");
- }
- }
package servletTest;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class CookieServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
super.doGet(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String userName = req.getParameter("userName");
String password = req.getParameter("password");
}
}
在这个代码中，自己新建了一个CookieServlet类，集成了httpservlet并重写doPost方法，在方法里获取userName和password。
截止到这里，看起来都非常的简单，不论是页面还是java代码都不难理解。但是如果只是这样的话，实际上是不行的，还需要配置web.xml文件才能让前后台联系起来，成功的实现交互。web.xml如下：
- <?xml version="1.0" encoding="UTF-8"?>
- <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
- xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
- xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
- id="WebApp_ID" version="2.5">
- <display-name>cookieTest</display-name>
- <servlet>
- <servlet-name>login</servlet-name>
- <servlet-class>servletTest.CookieServlet</servlet-class>
- </servlet>
- <servlet-mapping>
- <servlet-name>login</servlet-name>
- <url-pattern>/cookieServlet</url-pattern>
- </servlet-mapping>
- <welcome-file-list>
- <welcome-file>index.html</welcome-file>
- </welcome-file-list>
- </web-app>
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
id="WebApp_ID" version="2.5">
<display-name>cookieTest</display-name>
<servlet>
<servlet-name>login</servlet-name>
<servlet-class>servletTest.CookieServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>/cookieServlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>
</web-app>
这里边，首先要注册一个servlet，也就是下边这个：
<servlet>
<servlet-name>login</servlet-name>
<servlet-class>servletTest.CookieServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>/cookieServlet</url-pattern>
</servlet-mapping>
It can be seen that in my case, the corresponding <servlet-name> is login, so web.xml is looking for <servlet> containing <servlet-name>login</servlet-name> according to this login .
When you find this <servlet>, you can get the <servlet-class>servletTest.CookieServlet</servlet-class>, where the full path of the background servlet class we wrote is written in the <servlet-class>. It is the full package name plus the class name.
So, with this configuration, our program knows which background code the corresponding request should go to, so as to achieve association and interaction.