servlet_4

过滤器入门
	过滤器的概念及执行基本流程
	过滤器的使用场景
	过滤器的实现及基本配置


过滤器链
	过滤器链的配置
		使用注解的方式无法保证过滤器链的执行顺序，所以只能使用web.xml的配置
		按照出现在web.xml的filter-mapping顺序依次经过过滤器
		
异步过滤器
	与异步servlet类似
	
	异步过滤器的配置
	注解方式：设置@webfilter的属性asyncsupport属性为true
	web.xml方式：

与请求分派协作
	dispatcherTypes=DispatcherType.INCLUDE
	

包装器
	包装器的概念
	包装器类的使用
	
	在servlet api中提供了4个包装器类
	与装饰器的设计模式相类似
	允许将任何方法都包装到servletrequest...之中
	
	javax.servlet.ServletRequestWrapper，在其后加wrapper

一、servlet

package com.fgy;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/servlet6")
public class Servlet6 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println(request.getParameter("content"));
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

===============================================
二、过滤器

package com.fgy;

import java.io.IOException;

import javax.servlet.DispatcherType;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;


@WebFilter(urlPatterns="*")
public class Filter2 implements Filter {

    public void destroy() {
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        chain.doFilter(new MyWrapper((HttpServletRequest) request), response);
    }

    public void init(FilterConfig fConfig) throws ServletException {
    }

}

=============================================
三、包装器
进行修改，实现将请求参数的值1替换为one

package com.fgy;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class MyWrapper extends HttpServletRequestWrapper {

    private HttpServletRequest request;

    public MyWrapper(HttpServletRequest request) {
        super(request);
        this.request = request;
    }

    @Override
    public String getParameter(String name) {
        String value = request.getParameter(name);
        return value.replaceAll("1", "one");
    }
}