Java子线程调用RequestContextHolder.getRequestAttributes()方法问题详解

2022-11-13 17:11:05 线程调用详解

相信很多开发过程中都用过RequestContextHolder.getRequestAttributes()，没错，我也经常用，但今天出现了问题，获取到的实例是空的

原因是因为我新开了一个子线程，在子线程调用了RequestContextHolder.getRequestAttributes()。实际获取到的是空的

然后查看了源码

ThreadLocal获取。一个请求到达容器后，spring会把该请求Request实例通过setRequestAttributes方法把Request实例放入该请求线程内ThreadLocalMap中，然后就可以通过静态方法取到。原理就是ThreadLocal，但ThreadLocal不能让子线程继承ThreadLocalMap信息，可以使用InherbritableThreadLocal实现子线程信息传递。

Spring Boot 默认使用ThreadLocal把Request设置进请求线程中，这样如果在请求方法里面另起一个子线程然后再通过getRequestAttributes方法获取，是获取不到的

如果想要在子线程获取,设置inheritable=true即可，但我一直没找到在哪里可以设置，于是自己就写了个工具类来让子线程获取，思路是自定义一个注解，拦截注解，将父线程的ServletRequestAttributes给InheritableThreadLocal，然后在子线程即可获取

package com.shinedata.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface RequestInheritableThread {
}

aop

package com.shinedata.aop;
import com.shinedata.util.context.RequestHolder;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.stereotype.Component;
import org.springframework.WEB.context.request.ServletRequestAttributes;
@Aspect
@Component
public class RequestHolderAspect {
    @Before("@annotation(com.shinedata.annotation.RequestInheritableThread)")
    public void doBefore(JoinPoint joinPoint) {
        ServletRequestAttributes servletRequestAttributes = RequestHolder.getServletRequestAttributes();
        RequestHolder.setServletRequestAttributes(servletRequestAttributes);
    }
    @After("@annotation(com.shinedata.annotation.RequestInheritableThread)")
    public void doAfter(JoinPoint joinPoint) {
        RequestHolder.removeServletRequestAttributes();
    }
}

工具类

package com.shinedata.util.context;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.context.request.RequestAttributes;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;
import javax.servlet.Http.httpservletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.util.HashMap;
import java.util.Map;
import java.util.StringTokenizer;

public class RequestHolder {
    private static final Logger logger = LoggerFactory.getLogger(RequestHolder.class);
    public static final String GET = "GET";
    public static final String POST = "POST";
    public static final String UTF8 = "UTF-8";
    public static InheritableThreadLocal<ServletRequestAttributes> servletRequestAttributesInheritableThreadLocal= new InheritableThreadLocal();
    public static HttpServletRequest getRequest() {
        return getServletRequestAttributes().getRequest();
    }
    public static HttpServletResponse getResponse() {
        return getServletRequestAttributes().getResponse();
    }
    public static ServletRequestAttributes setServletRequestAttributes(ServletRequestAttributes servletRequestAttributes) {
        servletRequestAttributesInheritableThreadLocal.set(servletRequestAttributes);
        return servletRequestAttributes;
    }
    public static void removeServletRequestAttributes() {
        servletRequestAttributesInheritableThreadLocal.remove();
    }
    public static ServletRequestAttributes getServletRequestAttributes() {
        ServletRequestAttributes requestAttributes = (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
        if(requestAttributes==null){
            requestAttributes=servletRequestAttributesInheritableThreadLocal.get();
        }
        return requestAttributes;
    }
}

需要在子线程获取ServletRequestAttributes使用的时候在父方法贴个注解@RequestInheritableThread就行了，父方法里面即使开子线程，子线程里面也能获取ServletRequestAttributes

补充第二种解决办法,在开启新线程之前，将RequestAttributes对象设置为子线程共享

//开启新线程之前，添加代码：
ServletRequestAttributes sra = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
RequestContextHolder.setRequestAttributes(sra, true);

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