Servlet

Servlet的实现方式

• 实现 javax.servlet.Servlet

    @Override
    public void destroy() {}
    @Override
    public ServletConfig getServletConfig() {
        return null;
    }
    @Override
    public String getServletInfo() {
        return null;
    }
    @Override
    public void init(ServletConfig config) throws ServletException {    }
    @Override
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException {
    }
  

• 继承 javax.servlet.GenericServlet (其实就是封装了ServletConfig的方法)

    public class Demo extends GenericServlet{
    @Override
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException {
    }
  }
  

• 继承 javax.servlet.http.HttpServlet (先调用service方法在调用doGet或者doPost 如果没有覆盖405哦)

    @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 {
        super.doPost(req, resp);
    }
  
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        super.service(req, resp);
    }
  

访问doGet方法但是没有重写

生命周期方法
init() 仅仅调用一次
service() 每次处理请求都会被调用
destroy() 服务器停止之前
实例化是单利模式，线程不安全。

---

浏览器访问Servlet

• web.xml
  • servlet

  <servlet>
        <servlet-name>demo</servlet-name>
        <servlet-class>com.suse.yuxin.servlet.Demo</servlet-class>
        <load-on-startup>servlet的启动顺序 0 服务器启动就创建</load-on-startup>
    </servlet> 
  

  • servlet-mapping

    <servlet-mapping>
        <servlet-name>demo</servlet-name>
        <url-pattern>/demo</url-pattern>
        <url-pattern>/demo1</url-pattern>  //可以匹配多个路径
    </servlet-mapping>
    

---

ServletConfig(servlet的配置信息[web.xml中该servlet配置信息]将会被加载进去)

<servlet>
        <servlet-name>demo</servlet-name>
        <servlet-class>com.suse.yuxin.servlet.Demo</servlet-class>
        <init-param>
            <param-name>test</param-name>
            <param-value>test</param-value>
        </init-param>
</servlet> 
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
config.getServletName(); // demo
config.getInitParameter("test"); // test
config.getServletContext();

---

ServletContext(一个项目只有一个ServletContext)

• 域对象功能 保存和获取数据
• 获取应用的初始化参数

   <web-app>
      <context-param>
        <param-name>test</param-name>
        <param-value>test</param-value>
      </context-param>
   </web-app>
  ------------------------------
    getInitParameter("test");
  

• 获取路径

     getServletContext().getRealPath("");
  

---

Response

• 发送状态码

resp.sendError(404,"没有找到资源");//用于发送404 500等错误码
resp.setStatus(302);//用于发送成功的状态码

- 响应头信息**一般是一个头一个值也有一个头多个值**
```java
resp.setHeader("Refresh","test");//用于单个值
resp.addHeader("xxx", "value");//用于多个值

• 重定向

  resp.sendRedirect("/demo1");
  ----------------------------------------
  resp.setHeader("Location", "/demo1");
  resp.setStatus(302);
  

• 输出流

resp.getOutputStream().write("hello word".getBytes());
resp.getWriter().write("hello word");

- - -
###Request
- 获取客户端ip
```java
req.getRemoteAddr(); 

• 获取请求头

  req.getHeader(String name);
  //可以使用**refresh**请求头来防止倒链  refresh 指的是该请求是从哪个界面传过来的
  

• 获取参数

  req.getParameter("");
  req.getParameterValues("");