SpringBoot 过滤器filter实现

1、SpringBoot启动默认加载的Filter

• characterEncodingFilter
• hiddenHttpMethodFilter
• httpPutFormContentFilter
• requestContextFilter

2、Filter执行顺序

Ordered.HIGHEST_PRECEDENCE
Ordered.LOWEST_PRECEDENCE

低位值意味着更高的优先级 Higher values are interpreted as lower priority
自定义Filter，避免和默认的Filter优先级一样，不然会冲突

3、自定义filter实现

方法一：

第一步：启动类里面增加 @ServletComponentScan，进行扫描

第二步：新建一个MyFilter类实现Filter接口，重写方法，方法上加注解@WebFilter

@WebFilter(filterName = "myFilter2",urlPatterns = "/api/v2/*")
@Order(Ordered.LOWEST_PRECEDENCE -10)
public class MyFilter2 implements Filter {


    /**
     * filter启动执行，只执行一次
     * @param filterConfig
     * @throws ServletException
     */
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

        System.out.println("MyFilter2 ----------> init");
    }

    /**
     * filter拦截执行，每次拦截都会执行
     * @param servletRequest
     * @param servletResponse
     * @param filterChain
     * @throws IOException
     * @throws ServletException
     */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        System.out.println("MyFilter2 ----------> doFilter");

        //放行
        filterChain.doFilter(servletRequest,servletResponse);
    }

    /**
     * filter关闭执行，只执行一次
     */
    @Override
    public void destroy() {

        System.out.println("MyFilter2 ----------> destroy");
    }
}

场景：权限控制、用户登录(非前端后端分离场景)等

---

方法二：

第一步：创建一个类MyFilter实现FIlter接口，重写方法

public class MyFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

        System.out.println("MyFilter1 ----------> init");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("MyFilter1 ----------> doFilter");

        //放行
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {
        System.out.println("MyFilter1 ----------> destroy");

    }
}

第二步：在启动主类引入编写的Filter

@SpringBootApplication
@ServletComponentScan
public class FilterApplication {

    public static void main(String[] args) {
        SpringApplication.run(FilterApplication.class, args);
    }

    @Bean
    public FilterRegistrationBean myFilterRegistration(){
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        filterRegistrationBean.setFilter(new MyFilter());
        //定义拦截路径
        filterRegistrationBean.addUrlPatterns("/api/v1/*");
        //初始化参数
        filterRegistrationBean.addInitParameter("paramName", "paramValue");
        //定义拦截器名
        filterRegistrationBean.setName("MyFilter2");
        //定义拦截顺序，值越小越先执行
        filterRegistrationBean.setOrder(Ordered.HIGHEST_PRECEDENCE);
        return filterRegistrationBean;
    }
}

方法一是基于Servlet3.0的注解进行配置，使用起来更简单；方法二是注入Bean的方式实现拦截器的功能，将传统的xml配置拦截器的方式转为方法的实现

传统的Filter加载方式

filter的组成部分

• filter配置类
• 拦截的路径
• 初始化参数
• 忽略的路径

filter的配置

<filter>
   <filter-name>MyFilter</filter-name>
    <filter-class>com.dtdx.filter.demo1.MyFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>MyFilter</filter-name>
  <url-pattern>/*</url-pattern>
  <init-param>
    <param-name>paramName</param-name>
    <param-value>paramValue</param-value>
  </init-param>
</filter-mapping>