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SpringBoot 注入实例变量Request线程安全吗？

Spring全家桶实战案例

2021-09-08

导读：在Springboot中Controller中你是如何使用Request，Response对象的？

环境：SpringBoot2.3.9.RELEASE

测试Controller类

@RestController@RequestMapping("/message")public class MessageController {    @Resource  private HttpServletRequest request ;    @PostMapping("/resolver")  public Object resolver(@RequestBody Users user) {    System.out.println(request) ;    return user ;  }}

Debug模式调试代码查看Request到底是撒

通过调试，request对象实际注入的是一个代理对象
ObjectFactoryDelegatingInvocationHandler，查看该类源码：

private static class ObjectFactoryDelegatingInvocationHandler implements InvocationHandler, Serializable {
    private final ObjectFactory<?> objectFactory;
    public ObjectFactoryDelegatingInvocationHandler(ObjectFactory<?> objectFactory) {      this.objectFactory = objectFactory;    }
    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {      String methodName = method.getName();      if (methodName.equals("equals")) {        // Only consider equal when proxies are identical.        return (proxy == args[0]);      }      else if (methodName.equals("hashCode")) {        // Use hashCode of proxy.        return System.identityHashCode(proxy);      }      else if (methodName.equals("toString")) {        return this.objectFactory.toString();      }      try {        return method.invoke(this.objectFactory.getObject(), args);      }      catch (InvocationTargetException ex) {        throw ex.getTargetException();      }    }}

这是通过JDK的动态代理来实现的，该类有个属性ObjectFactory，通过名称也能也能猜出是一个对象工厂类，根据上面的调试也知道了，这里的objectFactory对象实际是RequestObjectFactory，通过这个类的.getObject()方法来获取真实的Request对象。

RequestObjectFactory源码：

@SuppressWarnings("serial")private static class RequestObjectFactory implements ObjectFactory<ServletRequest>, Serializable {
  @Override  public ServletRequest getObject() {    return currentRequestAttributes().getRequest();  }
  @Override  public String toString() {    return "Current HttpServletRequest";  }}

currentRequestAttributes()方法：

private static ServletRequestAttributes currentRequestAttributes() {    RequestAttributes requestAttr = RequestContextHolder.currentRequestAttributes();    if (!(requestAttr instanceof ServletRequestAttributes)) {      throw new IllegalStateException("Current request is not a servlet request");    }    return (ServletRequestAttributes) requestAttr;}

currentRequestAttributes()方法：

public static RequestAttributes currentRequestAttributes() throws IllegalStateException {    RequestAttributes attributes = getRequestAttributes();    if (attributes == null) {      if (jsfPresent) {        attributes = FacesRequestAttributesFactory.getFacesRequestAttributes();      }      if (attributes == null) {        throw new IllegalStateException("No thread-bound request found: " +            "Are you referring to request attributes outside of an actual web request, " +            "or processing a request outside of the originally receiving thread? " +            "If you are actually operating within a web request and still receive this message, " +            "your code is probably running outside of DispatcherServlet: " +            "In this case, use RequestContextListener or RequestContextFilter to expose the current request.");      }    }    return attributes;}

getRequestAttributes()方法：

public static RequestAttributes getRequestAttributes() {    RequestAttributes attributes = requestAttributesHolder.get();    if (attributes == null) {      attributes = inheritableRequestAttributesHolder.get();    }    return attributes;}

源码跟踪到这里也就知道了，真实的HttpServletRequest对象是被存入在ThreadLocal对象中，线程本地变量与线程绑定了，也就是在使用Request对象时，都会从ThreadLocal中获取。

接下来看看这个HttpServletRequest对象是什么时候存入ThreadLocal中的。

Servlet处理流程：请求----》service() ----》doXXX()

SpringMVC核心控制器类DispatcherServlet的父类FrameworkServlet

FrameworkServlet类中对应的doXXX方法都有一行processRequest方法调用

processRequest方法：

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException {
    long startTime = System.currentTimeMillis();    Throwable failureCause = null;
    LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();    LocaleContext localeContext = buildLocaleContext(request);
    RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();    ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);    asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
    initContextHolders(request, localeContext, requestAttributes);
    try {      doService(request, response);    }    catch (ServletException | IOException ex) {      failureCause = ex;      throw ex;    } catch (Throwable ex) {      failureCause = ex;      throw new NestedServletException("Request processing failed", ex);    } finally {      resetContextHolders(request, previousLocaleContext, previousAttributes);      if (requestAttributes != null) {        requestAttributes.requestCompleted();      }      logResult(request, response, failureCause, asyncManager);      publishRequestHandledEvent(request, response, startTime, failureCause);    }}

下面两行代码是来创建ServletRequestAttributes对象

RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

buildRequestAttributes()方法

protected ServletRequestAttributes buildRequestAttributes(HttpServletRequest request,      @Nullable HttpServletResponse response, @Nullable RequestAttributes previousAttributes) {
    if (previousAttributes == null || previousAttributes instanceof ServletRequestAttributes) {      return new ServletRequestAttributes(request, response);    }    else {      return null;  // preserve the pre-bound RequestAttributes instance    }}

在这里将request和response对象都存入到了ServletRequestAttributes对象中。

接着进入initContextHolders()方法

private void initContextHolders(HttpServletRequest request,      @Nullable LocaleContext localeContext, @Nullable RequestAttributes requestAttributes) {
    if (localeContext != null) {      LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);    }    if (requestAttributes != null) {      RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);    }}

进入
RequestContextHolder.setRequestAttributes(requestAttributes,
this.threadContextInheritable);这行代码

public static void setRequestAttributes(@Nullable RequestAttributes attributes, boolean inheritable) {    if (attributes == null) {      resetRequestAttributes();    }    else {      if (inheritable) {        inheritableRequestAttributesHolder.set(attributes);        requestAttributesHolder.remove();      }      else {        requestAttributesHolder.set(attributes);        inheritableRequestAttributesHolder.remove();      }    }}