ThreadLocal和InheritableThreadLocal深入探究（二）在Spring中的应用

柔情只为你懂 2022-03-17 08:27 353阅读 0赞

## ThreadLocal和InheritableThreadLocal深入探究（二）在Spring中的应用 ##

`Spring`中`RequestContextHolder`对`ThreadLocal`和`InheritableThreadLocal`的实现：

`org.springframework.web.context.request.RequestContextHolder`

> 该类暴露了`web`请求属性约束的支持，即请求中属性值将会被子类线程继承，当开关`inheritable`打开的时候

>     Holder class to expose the web request in the form of a thread-bound
>     {@link RequestAttributes} object. The request will be inherited
>     by any child threads spawned by the current thread if the
>     {@code inheritable} flag is set to {@code true}.

### 源码分析 ###

public abstract class RequestContextHolder  { 
        // 定义NamedThreadLocal
        private static final ThreadLocal<RequestAttributes> requestAttributesHolder =
            new NamedThreadLocal<RequestAttributes>("Request attributes");
        // 定义NamedInheritableThreadLocal
        private static final ThreadLocal<RequestAttributes> inheritableRequestAttributesHolder =
            new NamedInheritableThreadLocal<RequestAttributes>("Request context");
    
        // attributes表示开关
        public static void setRequestAttributes(RequestAttributes attributes, boolean inheritable) { 
            if (attributes == null) { 
                resetRequestAttributes();
            }
            else { 
                // 开关打开采用NamedInheritableThreadLocal
                if (inheritable) { 
                    inheritableRequestAttributesHolder.set(attributes);
                    requestAttributesHolder.remove();
                }
                // 开关关闭采用NamedThreadLocal
                else { 
                    requestAttributesHolder.set(attributes);
                    inheritableRequestAttributesHolder.remove();
                }
            }
        }

public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware { 
        // 设置 threadContextInheritable 默认值
        private boolean threadContextInheritable = false;
        //web servlet 的开关默认值为 false
        public void setThreadContextInheritable(boolean threadContextInheritable) { 
            this.threadContextInheritable = threadContextInheritable;
        }
        ...
            private void initContextHolders(
            HttpServletRequest request, LocaleContext localeContext, RequestAttributes requestAttributes) { 
    
            // setLocaleContext
            if (localeContext != null) { 
                LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);
            }
            // setRequestAttributes 设置ThreadLocal和InheritableThreadLocal的开关this.threadContextInheritable
            if (requestAttributes != null) { 
                // 实现对RequestContextHolder初始化的支持
                RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);
            }
            if (logger.isTraceEnabled()) { 
                logger.trace("Bound request context to thread: " + request);
            }
        }
        ...
    }

### 总结 ###

> 经过对`Spring`源码的分析，我们得出在`Spring Web Mvc`中对于`ThreadLocal`父子类继承关系的动态设置，以及调用、实现。

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[https_blog.csdn.net_shang_xs_article_details_87874477]: https://blog.csdn.net/shang_xs/article/details/87874477
[https_blog.csdn.net_shang_xs_article_details_87889079]: https://blog.csdn.net/shang_xs/article/details/87889079
[https_blog.csdn.net_shang_xs_article_details_87889285]: https://blog.csdn.net/shang_xs/article/details/87889285