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("");