多个Filter中doFilter方法的执行顺序（二）

书接上篇博客：多个Filter中doFilter方法的执行顺序（一）

一、Filter异常断链

假设有3个 Filter，分别为Filter1~3，顺序依次为 1、2、3（即 1 在最前，3 在最后），当执行到Filter3时抛出了异常（又或者具体Servlet执行时抛出了异常），具体代码示例如下：

import jakarta.servlet.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

import java.io.IOException;

@Component
@Order(1)
public class Filter1 implements Filter {

    private static final Logger log = LoggerFactory.getLogger(Filter1.class);

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        log.info("Filter1 Before");
        chain.doFilter(request, response);
        log.info("Filter1 After");
    }
}

---

@Component
@Order(2)
public class Filter2 implements Filter {

    private static final Logger log = LoggerFactory.getLogger(Filter2.class);

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        log.info("Filter2 Before");
        chain.doFilter(request, response);
        log.info("Filter2 After");
    }
}

---

@Component
@Order(3)
public class Filter3 implements Filter {

    private static final Logger log = LoggerFactory.getLogger(Filter3.class);

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        log.info("Filter3 Before");
        //抛出异常
        if (true) {
        	throw new RuntimeException("Exception in Filter3");
        }
        chain.doFilter(request, response);
        log.info("Filter3 After");
    }
}

它们的 doFilter 执行顺序如下：

1. 请求进入时，先执行 Filter1 的 doFilter 方法。
2. 在 Filter1 的 chain.doFilter(request, response) 处，进入 Filter2 的 doFilter。
3. 在 Filter2 的 chain.doFilter(request, response) 处，进入 Filter3 的 doFilter。
4. 在 Filter3 抛出业务异常，结束Filter3及后续Servlet的执行。
5. 无法返回Filter2、Filter1，执行它们在 chain.doFilter 之后的代码。

具体的执行日志如下：

Filter1 Before
Filter2 Before
Filter3 Before

二、Filter异常补偿

如果希望即便后续的Filter或Servlet抛出了异常，优先级更高的Filter的chain.doFilter(request, response) 之后的处理逻辑仍可正常执行，可通过try..finally的形式，调整后的代码如下：

import jakarta.servlet.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

import java.io.IOException;

@Component
@Order(1)
public class Filter1 implements Filter {

    private static final Logger log = LoggerFactory.getLogger(Filter1.class);

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        try {
            log.info("Filter1 Before");
            chain.doFilter(request, response);
        } finally {
            log.info("Filter1 After");
        }
    }
}

---

@Component
@Order(2)
public class Filter2 implements Filter {

    private static final Logger log = LoggerFactory.getLogger(Filter2.class);

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        try {
            log.info("Filter2 Before");
            chain.doFilter(request, response);
        } finally {
            log.info("Filter2 After");
        }
    }
}


---

@Component
@Order(3)
public class Filter3 implements Filter {

    private static final Logger log = LoggerFactory.getLogger(Filter3.class);

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        try {
            log.info("Filter3 Before");
            if (true) {
                throw new RuntimeException("Exception in Filter3");
            }
            chain.doFilter(request, response);
        } finally {
            log.info("Filter3 After");
        }
    }
}

调整后具体的执行日志如下：

Filter1 Before
Filter2 Before
Filter3 Before
Filter3 After
Filter2 After
Filter1 After