Javaweb三大组件之一 servlet

1.servlet基本使用

　　注意：单例：init只会执行一次

　　　　   线程不安全

1.1 创建方式

（1）实现servlet接口【不使用】

package cn.getword.servlet;

import javax.servlet.*;
import java.io.IOException;

public class LoginServlet implements Servlet {
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        System.out.println("init servlet...");
    }

    @Override
    public ServletConfig getServletConfig() {
        return null;
    }

    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        servletResponse.getWriter().print("hello servlet");
    }

    @Override
    public String getServletInfo() {
        return null;
    }

    @Override
    public void destroy() {

    }
}

　　init方法用来配置servlet初始化参数：

　　第一次访问servlet时，进行servlet实例化，执行init方法。

需要服务器启动时创建servlet实例：在web.xml中配置：load-on-startup ：非负整数

<servlet>
    <servlet-name>login</servlet-name>
    <servlet-class>cn.getword.servlet.LoginServlet</servlet-class>
    <init-param>
        <param-name>charset</param-name>
        <param-value>utf-8</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>login</servlet-name>
    <url-pattern>/login</url-pattern>
</servlet-mapping>

　　url-pattern的写法：*.do  , /servlet/*    【通配符 *  要么放在最前面，要么放在最后面】

　　获取参数信息：　　

    private ServletConfig config;  //将配置对象保存下来
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        System.out.println("init servlet...");
        this.config = servletConfig;
        servletConfig.getInitParameter("charset");
    }

　　服务终止前执行destroy方法，用于关闭非内存资源。

（2）继承GenericServlet类【不使用】

package cn.getword.servlet;

import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import java.io.IOException;

public class Login2Servlet extends GenericServlet {
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {

    }
}

（3） 继承HTTPServlet类【使用】  注解或配置文件

package cn.getword.servlet;

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 java.io.IOException;

@WebServlet(name = "Login3Servlet", urlPatterns = {"/login3"})
public class Login3Servlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().print("你好，servlet");
    }
}

　　通过request获取session对象：

Session session = request.getSession();

获取参数信息：

@WebServlet("/register")
public class RegisterServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        String username = request.getParameter("username");
        String phone = request.getParameter("username");
        String pwd = request.getParameter("username");
        String[] hobby = request.getParameterValues("hobby");//获取复选框值
        String gender = request.getParameter("gender");
        String course = request.getParameter("course");
        response.getWriter().print("hello");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    }
}

2. 解决乱码

　　String name = request.getParameter("name");

　方法一：转码

name = new String(name.getBytes("ISO-8859-1"));

　方法二：【推荐】

request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
String username = request.getParameter("username");

3. 转发

　

request.getRequestDispatcher("").forward(request, response);

注意：不可以跨域

4.重定向

response.sendRedirect("");

注意：可以跨域

5.cookie【服务器端操作】

添加cookie：【使用response向客户端写入cookie】

response.addCookie(new Cookie("userid", "10"));

获取cookie：【使用request获取cookie】

request.getCookies()

6.session

（1）使用方法

session.setAttribute("userid", "1");  
session.getAttribute("userid");
session.removeAttribute(key);

注意：作用范围为回话范围。

（2）强制使得session失效,一般用于用户注销

session.invalidate();

7. pageContext

获取其他内置对象：

pageContext.getRequest();
pageContext.getResponse();
pageContext.getServletConfig();

8.application对象　　

在web.xml中配置web项目的全局初始化参数：

    <context-param>
        <param-name>jdbc</param-name>
        <param-value></param-value>
    </context-param>

使用application对象获取参数信息：

  <%
    Enumeration<String> initParameterNames = application.getInitParameterNames();
    while(initParameterNames.hasMoreElements()){
        String key = initParameterNames.nextElement();
        out.print(key+":"+application.getInitParameter(key)+"<br />");
    }
  %>

end