Spring Boot - Servlet Filter Spring Boot – Servlet Filter | GeeksforGeeks

这是官方说明。要注意！！！⚠️ 

使用时，在 porn.xml 文件加了引用坐标也无效

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
        </dependency>

且，javax.servlet 缺省的 init and destroy 的接口也去掉了 default 关键词。

代码变更为

package biz.baijing.filter;

import jakarta.servlet.Filter;
import jakarta.servlet.FilterChain;
import jakarta.servlet.FilterConfig;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;
import org.springframework.stereotype.Component;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

@Component
@WebFilter(urlPatterns = "/*")
public class UniFilter implements jakarta.servlet.Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("UniFilter init 启动");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("DoFilter ， start 启动中");

        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    public void destroy() {
        System.out.println("UniFilter destroy 关闭");
    }
}

这里的 init and destroy 是「 default 」定义的。

Filter 的源代码

package jakarta.servlet;

import java.io.IOException;

public interface Filter {
    default void init(FilterConfig filterConfig) throws ServletException {
    }

    void doFilter(ServletRequest var1, ServletResponse var2, FilterChain var3) throws IOException, ServletException;

    default void destroy() {
    }
}