带你快速上手Servlet

 String getServletName(); ---获取当前Servlet在web.xml中配置的名字
 
    ServletContext getServletContext();---获取当前Servlet指定名称的初始化参数的值
 
    String getInitParameter(String var1);---获取当前Servlet所有初始化参数的名字组成的枚举
 
    Enumeration<String> getInitParameterNames();---获取代表当前web应用的ServletContext对象

 @Override
    public void init(ServletConfig servletConfig) throws ServletException {
//        1、可以获取Servlet程序的别名Servlet-name的值
        System.out.println(servletConfig.getServletName());
//        2、获取初始化参数init-param
        System.out.println(servletConfig.getInitParameter("username"));
//        3、获取ServletContext对象
        System.out.println(servletConfig.getServletContext());
        System.out.println("2、执行初始化方法");
    }

public class ContextServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //1、 获取web.xml中配置上下文参数context-param
        ServletContext servletContext = getServletConfig().getServletContext();
        String username = servletContext.getInitParameter("username");
        System.out.println("context-param参数的username"+username);
 
    }
}

<!--    context-param 是上下文参数（它是属于整个web工程）-->
    <context-param>
        <param-name>username</param-name>
        <param-value>context</param-value>
    </context-param>

public class ContextServlet1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
    }
 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取ServletContext对象
        ServletContext context = getServletContext();
        System.out.println("保存之前：Context1 获取key1的值是:"+context.getAttribute("key1"));
        context.setAttribute("key1","value1");
        System.out.println("Context1中获取域数据key1的值是:"+context.getAttribute("key1"));
 
    }
}

保存之前：Context1 获取key1的值是:null
Context1中获取域数据key1的值是:value1
Context2中获取域数据key1的值是:value1

public class HelloServlet implements Servlet {
    public HelloServlet() {
        System.out.println("1、执行构造器方法");
    }
 
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        System.out.println("2、执行初始化方法");
    }
 
    @Override
    public ServletConfig getServletConfig() {
        return null;
    }
 
    //service方法是专门用来处理请求和响应的
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.out.println("3、hello servlet 被访问了");
    }
 
    @Override
    public String getServletInfo() {
        return null;
    }
 
    @Override
    public void destroy() {
        System.out.println(" 4、执行销毁方法");
    }
}

    //service方法是专门用来处理请求和响应的
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.out.println("3、hello servlet 被访问了");
        HttpServletRequest httpServletRequest=(HttpServletRequest)servletRequest;
        String method = httpServletRequest.getMethod();
        if ("Get".equals(method)){
            
        }
        if ("POST".equals(method)){
            
        }
    }