13.适配器

1.Servlet程序为了不再继承Servlet接口中不必要的方法。实现适配器
2.模仿写一个GenericServlet 适配器

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

/**
 * GenericServlet是一个适配器
 * 以后无需实现Servlet接口，直接继承适配器，重写service方法。
 */
public abstract class GenericServlet implements Servlet
{
    private ServletConfig config;
    @Override
    public final void init(ServletConfig servletConfig) throws ServletException {
        this.config=servletConfig;
        //final关键字不让子类复写该方法
        // 若子类复写了，config就没有赋值，调用getServletConfig为空指针。
        this.init();
    }

    /**
     * 若在初始化时执行一段程序，建议复写无参init方法即可
     */
    public void init(){}

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

    @Override
    public abstract void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException;

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

    @Override
    public void destroy() {

    }

    //-------------------扩展方法，方便子类的使用-------------------------------------
    public ServletContext getServletContext(){
        return getServletConfig().getServletContext();
    }
    //-------------
}

3.继承适配器的实现子类

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

public class HelloServlet extends javax.servlet.GenericServlet
{
    @Override
    public void init() {
        //初始化时执行的内容
        System.out.println("helloServlet's init.....");
    }

    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        servletResponse.setContentType("text/html;charset=UTF-8");
        PrintWriter out = servletResponse.getWriter();
        out.println("Hello Word!");



    }
}