快捷導(dǎo)航

Java過(guò)濾器Filter詳解

更新時(shí)間：2021年08月25日 10:40:15 作者：木筆の園子

這篇文章主要介紹了java過(guò)濾器中Filter,發(fā)送請(qǐng)求時(shí)，如果有不符合的信息將會(huì)被filter進(jìn)行攔截，如果符合則會(huì)進(jìn)行放行。如果感興趣可以來(lái)學(xué)習(xí)一下

Filter學(xué)習(xí)

Filter功能

攔截jsp、靜態(tài)圖片文件、靜態(tài)html資源文件
實(shí)現(xiàn)URL級(jí)別的權(quán)限訪問(wèn)控制
過(guò)濾敏感詞匯
壓縮相應(yīng)信息

Filter的工作原理

看源碼可以看出來(lái)，F(xiàn)ilter接口中有3個(gè)方法：init、doFilter、destory

在這里插入圖片描述

init方法，初始化Filter，F(xiàn)ilter在服務(wù)器啟動(dòng)階段被實(shí)例化。并且調(diào)用init方法，init方法只執(zhí)行一次，因?yàn)镕ilter只被實(shí)例化一次。

destory方法也好理解，就是銷(xiāo)毀Filter，釋放內(nèi)存，在運(yùn)行結(jié)束時(shí)調(diào)用此方法當(dāng)。長(zhǎng)時(shí)間沒(méi)有用戶(hù)訪問(wèn)，或者項(xiàng)目重新部署，或者服務(wù)器重新啟動(dòng)的時(shí)候，會(huì)銷(xiāo)毀所有的Filter對(duì)象，銷(xiāo)毀之前會(huì)先調(diào)用Filter對(duì)象的destroy方法，完成銷(xiāo)毀前的準(zhǔn)備工作。也是只執(zhí)行一次。

doFilter方法提供給開(kāi)發(fā)者重寫(xiě)過(guò)濾邏輯。

多個(gè)Filter的實(shí)現(xiàn)

public class AFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("輸出filter2的init方法");
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        System.out.println("輸出filter2的doFilter方法之前");
        filterChain.doFilter(request, response);
        System.out.println("輸出filter2的doFilter方法之后");
    }
    @Override
    public void destroy() {
        System.out.println("輸出filter2的destroy方法");
    }
}

public class BFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("輸出filter1的init方法");
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        System.out.println("輸出filter1的doFilter方法之前");
        filterChain.doFilter(request, response);
        System.out.println("輸出filter1的doFilter方法之后");
    }
    @Override
    public void destroy() {
        System.out.println("輸出filter1的destroy方法");
    }
}

配置Filter的過(guò)濾順序，通過(guò)setOrder方法執(zhí)行FilterChain的順序，數(shù)字越小，優(yōu)先級(jí)越高。

@Configuration
public class WebConfig {
    @Bean
    public FilterRegistrationBean filter1() {
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        AFilter aFilter = new AFilter();
        filterRegistrationBean.setFilter(aFilter);
        filterRegistrationBean.setOrder(1);
        return filterRegistrationBean;
    }
    @Bean
    public FilterRegistrationBean filter2() {
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        BFilter bFilter = new BFilter();
        filterRegistrationBean.setFilter(bFilter);
        filterRegistrationBean.setOrder(2);
        return filterRegistrationBean;
    }
}