Springboot使用Filter以及踩過的坑

在Springboot中使用Filter有兩種方式，註解方式，註冊bean方式

一、註解@WebFilter

1、實現Filter介面（javax.servlet）

2、新增@WebFilter註解

3、啟動類新增@ServletComponentScan註解

附上程式碼：

第一個Filter：

@Slf4j
@WebFilter(filterName = "filter1", urlPatterns = {"/url1/*"})
public class Filter1_Filter implements Filter {

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

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("do filter1");
        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    
 
public void destroy() {
        
    }

}

第二個Filter：

@Slf4j
@WebFilter(filterName = "filter2", urlPatterns = {"/url2/*"})
public class Filter2_Filter implements Filter {

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

    @Override
    public
 
 void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("do filter2");
        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    public void destroy() {
        
    }

}

啟動類：

@SpringBootApplication
@ServletComponentScan
public class MyApplication {

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

}

下面說說我踩過的坑

1、不加@ServletComponentScan註解無法注入Filter，這個註解的作用就是去掃描@WebServlet、@WebFilter、@WebListener這類特殊註解。如果不加，spring容器是不會主動掃描的

2、多個Filter的執行順序，說出來你可能不信，這種註解方式實現的Filter是通過Filter的類名首字母來控制執行順序的，像Filter1_Filter就比Filter2_Filter先執行。但網上一些資料說，當Filter數量很多時，是沒有明確的執行順序的，所以這種方式還是放棄吧，推薦第二種

二、註冊bean

1、實現Filter介面

2、註冊Filter

下面附上程式碼：

第一個Filter：

@Slf4j
public class Filter1 implements Filter {

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

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("do filter1");
        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    public void destroy() {
        
    }

}

第二個Filter：

@Slf4j
public class Filter2 implements Filter {

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

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("do filter2");
        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    public void destroy() {
        
    }

}

註冊類：

@Configuration
public class FilterConfig {

    @Bean
    public Filter filter1(){
        return new Filter1();
    }

    @Bean
    public Filter filter2(){
        return new Filter2();
    }

    @Bean
    public FilterRegistrationBean setFilter1() {
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        filterRegistrationBean.setFilter(filter1());
        filterRegistrationBean.addUrlPatterns("/url1/*");
        filterRegistrationBean.setOrder(1);   //order的數值越小，在所有的filter中優先順序越高
        return filterRegistrationBean;
    }

    @Bean
    public FilterRegistrationBean setFilter2(){
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        filterRegistrationBean.setFilter(filter2());
        filterRegistrationBean.addUrlPatterns("/url2/*");
        filterRegistrationBean.setOrder(2);   //order的數值越小，在所有的filter中優先順序越高
        return filterRegistrationBean;
    }

}

這種方式就比較嚴謹了，通過filterRegistrationBean.setOrder(1)設定執行順序親測有效