1. Servlet处理各种请求

service：处理所有请求
doGet：处理GET请求
doPost：处理POST请求
doPut：处理PUT请求
doDelete：处理DELETE请求
doHead：处理HEAD请求
doOptions：处理OPTIONS请求

public class MyServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doGet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doPost");
    }

    @Override
    protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doDelete");
    }

    @Override
    protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doPut");
    }

    @Override
    protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doHead");
    }

    @Override
    protected void doOptions(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doOptions");
    }
}

如果你重写了service，又重写了doXxx，那么只有service会被调用

/** 只调用service */
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    System.out.println("service");
}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    System.out.println("doGet");
}

但是如果你在service中调用父类的service，则会发现，doXxx也会被调用。这说明，父类的service会根据请求的类型，调用对应的doXxx

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

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    System.out.println("doGet");
}

2. 405错误：请求方式不支持

如果调用了父类的service，你又没有重写相应的doXxx，则发起请求时，就返回HTTP Status 405 – Method Not Allowed，表示服务器无法处理该请求

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