过滤器的创建和执行顺序

8.1.1创建并配置过滤器

P143 重点是如何创建并配置（xml）

1.创建

public class EncodingFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
            servletRequest.setCharacterEncoding("UTF-8");
            servletResponse.setCharacterEncoding("UTF-8");
            filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {

    }
}

2.配置

• 注解方式：所有路径不能是多个*，可以配置多个过滤路径
• xml方式

3.注解方式

@WebFilter("/*")
@WebFilter(filterName = "myFilter",urlPatterns = {"/*"})

4.xml方式

<filter>
    <filter-name>hellohello</filter-name>
    <filter-class>demo.HelloServlet</filter-class>
</filter>
<filter-mapping>
    <filter-name>hellohello</filter-name>
    <url-pattern>/hellohello</url-pattern>
</filter-mapping>
<!--    可以配置多个路径-->
    <filter-mapping>
        <filter-name>hellohello</filter-name>
        <url-pattern>/hellohello2</url-pattern>
    </filter-mapping>

5.基于xml的案例

public class HelloServlet implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("我是过滤器");
    }

    @Override
    public void destroy() {

    }
}

8.1.2 执行过滤器的详细过程

图1 Filter执行过程图2

8.1.3过滤器执行顺序

过滤器链的执行顺序

• 先在web.xml中查找过滤器执行

在web.xml中，则按照配置的<filter-mapping>顺序执行

• 再在注解的过滤中中选择执行：就是按照包名类名等的顺序执行

@WebFilter 按字母序执行