(ps:前几个星期发生的事情)之前同事跟我说不要使用@Autowired方式注入HttpServletRequest(ps:我们的代码之前用的是第2种方式)。同事的意思大概是注入的HttpServletRequest对象是同一个而且存在线程安全问题。我保持质疑的态度，看了下源码，证明了@Autowired方式不存在线程安全问题，而@ModelAttribute方式存在线程安全问题。
观看本文章之前，最好看一下我上一篇写的文章：
1.通过循环引用问题来分析Spring源码
2.你真的了解Spring MVC处理请求流程吗?
public abstract class BaseController {
@Autowired
protected HttpSession httpSession;
@Autowired
protected HttpServletRequest request;
}
public abstract class BaseController1 {
protected HttpServletRequest request;
protected HttpServletResponse response;
protected HttpSession httpSession;
@ModelAttribute
public void init(HttpServletRequest request,
HttpServletResponse response,
HttpSession httpSession) {
this.request = request;
this.response = response;
this.httpSession = httpSession;
}
}
线程安全测试
@RequestMapping("/test")
@RestController
public class TestController extends BaseController {
@GetMapping("/1")
public void test1() throws InterruptedException {
// System.out.println("thread.id=" + Thread.currentThread().getId());
// System.out.println("thread.name=" + Thread.currentThread().getName());
// ServletRequestAttributes servletRequestAttributes =
// ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes());
//
// HttpServletRequest httpServletRequest = servletRequestAttributes.getRequest();
TimeUnit.SECONDS.sleep(10);
// System.out.println("base.request=" + request);
System.out.println("base.request.name=" + request.getParameter("name"));
}
@GetMapping("/2")
public void test2() throws InterruptedException {
// System.out.println("thread.id=" + Thread.currentThread().getId());
// System.out.println("thread.name=" + Thread.currentThread().getName());
// ServletRequestAttributes servletRequestAttributes =
// ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes());
//
// HttpServletRequest httpServletRequest = servletRequestAttributes.getRequest();
// System.out.println("base.request=" + request);
System.out.println("base.request.name=" + request.getParameter("name"));
}
@InitBinder
public void initBinder(WebDataBinder binder) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
binder.registerCustomEditor(Date.class, new CustomDateEditor(sdf, true));
}
}
通过JUC的CountDownLatch，模拟同一时刻100个并发请求。
public class Test {
public static void main(String[] args) {
CountDownLatch start = new CountDownLatch(1);
CountDownLatch end = new CountDownLatch(100);
CustomThreadPoolExecutor customThreadPoolExecutor = new CustomThreadPoolExecutor(
100, 100, 0L,
TimeUnit.SECONDS,
new ArrayBlockingQueue(100)
);
for (int i = 0; i < 100; i++) {
final int finalName = i;
CustomThreadPoolExecutor.CustomTask task = new CustomThreadPoolExecutor.CustomTask(
new Runnable() {
@Override
public void run() {
try {
start.await();
HttpUtil.get("http://localhost:8081/test/2?name=" + finalName);
} catch (Exception ex) {
ex.printStackTrace();
} finally {
end.countDown();
}
}
}
, "success");
customThreadPoolExecutor.submit(task);
}
start.countDown();
try {
end.await();
} catch (InterruptedException ex) {
ex.printStackTrace();
}
customThreadPoolExecutor.shutdown();
}
}
通过观看base.request.name的值并没有null值和存在值重复的现象，很肯定的说@Autowired注入的HttpServletRequest不存在线程安全问题。
base.request.name=78
base.request.name=20
base.request.name=76
base.request.name=49
base.request.name=82
base.request.name=12
base.request.name=80
base.request.name=91
base.request.name=92
base.request.name=30
base.request.name=28
base.request.name=36
base.request.name=41
base.request.name=73
base.request.name=29
base.request.name=2
base.request.name=81
base.request.name=43
base.request.name=35
base.request.name=22
base.request.name=6
base.request.name=27
base.request.name=17
base.request.name=70
base.request.name=65
base.request.name=84
base.request.name=14
base.request.name=54
base.request.name=67
base.request.name=19
base.request.name=21
base.request.name=66
base.request.name=11
base.request.name=53
base.request.name=9
base.request.name=72
base.request.name=64
base.request.name=0
base.request.name=44
base.request.name=89
base.request.name=77
base.request.name=48
base.request.name=1
base.request.name=8
base.request.name=74
base.request.name=46
base.request.name=88
base.request.name=26
base.request.name=24
base.request.name=62
base.request.name=61
base.request.name=51
base.request.name=96
base.request.name=33
base.request.name=45
base.request.name=5
base.request.name=95
base.request.name=68
base.request.name=60
base.request.name=56
base.request.name=42
base.request.name=57
base.request.name=10
base.request.name=55
base.request.name=90
base.request.name=47
base.request.name=97
base.request.name=40
base.request.name=85
base.request.name=86
base.request.name=69
base.request.name=98
base.request.name=13
base.request.name=32
base.request.name=37
base.request.name=4
base.request.name=23
base.request.name=50
base.request.name=38
base.request.name=59
base.request.name=99
base.request.name=71
base.request.name=25
base.request.name=58
base.request.name=34
base.request.name=7
base.request.name=93
base.request.name=31
base.request.name=3
base.request.name=39
base.request.name=75
base.request.name=94
base.request.name=83
base.request.name=63
base.request.name=79
base.request.name=16
base.request.name=52
base.request.name=15
base.request.name=87
base.request.name=18
很明显发现base.request.name的值存在null或者重复的现象，说明通过@ModelAttribute注入的HttpServletRequest存在线程安全问题。
base.request.name=97
base.request.name=59
base.request.name=63
base.request.name=14
base.request.name=82
base.request.name=49
base.request.name=86
base.request.name=13
base.request.name=99
base.request.name=29
base.request.name=45
base.request.name=85
base.request.name=8
base.request.name=35
base.request.name=69
base.request.name=70
base.request.name=16
base.request.name=21
base.request.name=74
base.request.name=20
base.request.name=34
base.request.name=23
base.request.name=96
base.request.name=19
base.request.name=67
base.request.name=15
base.request.name=27
base.request.name=43
base.request.name=39
base.request.name=47
base.request.name=87
base.request.name=71
base.request.name=41
base.request.name=38
base.request.name=null
base.request.name=31
base.request.name=32
base.request.name=76
base.request.name=55
base.request.name=75
base.request.name=93
base.request.name=null
base.request.name=56
base.request.name=1
base.request.name=18
base.request.name=89
base.request.name=65
base.request.name=10
base.request.name=78
base.request.name=null
base.request.name=80
base.request.name=24
base.request.name=88
base.request.name=88
base.request.name=44
base.request.name=53
base.request.name=58
base.request.name=61
base.request.name=60
base.request.name=37
base.request.name=92
base.request.name=42
base.request.name=11
base.request.name=68
base.request.name=72
base.request.name=91
base.request.name=79
base.request.name=33
base.request.name=66
base.request.name=54
base.request.name=40
base.request.name=94
base.request.name=46
base.request.name=83
base.request.name=17
base.request.name=64
base.request.name=26
base.request.name=90
base.request.name=7
base.request.name=62
base.request.name=57
base.request.name=73
base.request.name=98
base.request.name=30
base.request.name=6
base.request.name=2
base.request.name=28
base.request.name=5
base.request.name=95
base.request.name=9
base.request.name=3
base.request.name=51
base.request.name=4
base.request.name=52
base.request.name=12
base.request.name=25
base.request.name=36
base.request.name=84
base.request.name=81
base.request.name=50
源码分析
1.在Spring容器初始化中，refresh()方法会调用postProcessBeanFactory(beanFactory);。它是个模板方法，在BeanDefinition被装载后(所有BeanDefinition被加载，但是没有bean被实例化)，提供一个修改beanFactory容器的入口。这里还是贴下AbstractApplicationContext中的refresh()方法吧。
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// 1.Prepare this context for refreshing.
prepareRefresh();
// 2.Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 3.Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// 4.Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// 5.Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// 6.Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// 7.Initialize message source for this context.
initMessageSource();
// 8.Initialize event multicaster for this context.
initApplicationEventMulticaster();
// 9.Initialize other special beans in specific context subclasses.
onRefresh();
//10. Check for listener beans and register them.
registerListeners();
// 11.Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
//12. Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
2.由于postProcessBeanFactory是模板方法，它会被子类AbstractRefreshableWebApplicationContext重写。在AbstractRefreshableWebApplicationContext的postProcessBeanFactory()做以下几件事情。
1.注册ServletContextAwareProcessor。
2.注册需要忽略的依赖接口ServletContextAware、ServletConfigAware。
3.注册Web应用的作用域和环境配置信息。
@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
beanFactory.ignoreDependencyInterface(ServletContextAware.class);
beanFactory.ignoreDependencyInterface(ServletConfigAware.class);
WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
}
- WebApplicationContextUtils中的registerWebApplicationScopes()，beanFactory注册了request,application,session,globalSession作用域，也注册了需要解决的依赖：ServletRequest、ServletResponse、HttpSession、WebRequest。
public static void registerWebApplicationScopes(ConfigurableListableBeanFactory beanFactory, ServletContext sc) {
beanFactory.registerScope(WebApplicationContext.SCOPE_REQUEST, new RequestScope());
beanFactory.registerScope(WebApplicationContext.SCOPE_SESSION, new SessionScope(false));
beanFactory.registerScope(WebApplicationContext.SCOPE_GLOBAL_SESSION, new SessionScope(true));
if (sc != null) {
ServletContextScope appScope = new ServletContextScope(sc);
beanFactory.registerScope(WebApplicationContext.SCOPE_APPLICATION, appScope);
// Register as ServletContext attribute, for ContextCleanupListener to detect it.
sc.setAttribute(ServletContextScope.class.getName(), appScope);
}
beanFactory.registerResolvableDependency(ServletRequest.class, new RequestObjectFactory());
beanFactory.registerResolvableDependency(ServletResponse.class, new ResponseObjectFactory());
beanFactory.registerResolvableDependency(HttpSession.class, new SessionObjectFactory());
beanFactory.registerResolvableDependency(WebRequest.class, new WebRequestObjectFactory());
if (jsfPresent) {
FacesDependencyRegistrar.registerFacesDependencies(beanFactory);
}
}
4.RequestObjectFactory, ResponseObjectFactory, SessionObjectFactory都实现了ObjectFactory的接口，注入的值其实是getObject()的值。
/**
* Factory that exposes the current request object on demand.
*/
@SuppressWarnings("serial")
private static class RequestObjectFactory implements ObjectFactory, Serializable {
@Override
public ServletRequest getObject() {
return currentRequestAttributes().getRequest();
}
@Override
public String toString() {
return "Current HttpServletRequest";
}
}
/**
* Factory that exposes the current response object on demand.
*/
@SuppressWarnings("serial")
private static class ResponseObjectFactory implements ObjectFactory, Serializable {
@Override
public ServletResponse getObject() {
ServletResponse response = currentRequestAttributes().getResponse();
if (response == null) {
throw new IllegalStateException("Current servlet response not available - " +
"consider using RequestContextFilter instead of RequestContextListener");
}
return response;
}
@Override
public String toString() {
return "Current HttpServletResponse";
}
}
/**
* Factory that exposes the current session object on demand.
*/
@SuppressWarnings("serial")
private static class SessionObjectFactory implements ObjectFactory, Serializable {
@Override
public HttpSession getObject() {
return currentRequestAttributes().getRequest().getSession();
}
@Override
public String toString() {
return "Current HttpSession";
}
}
/**
* Factory that exposes the current WebRequest object on demand.
*/
@SuppressWarnings("serial")
private static class WebRequestObjectFactory implements ObjectFactory, Serializable {
@Override
public WebRequest getObject() {
ServletRequestAttributes requestAttr = currentRequestAttributes();
return new ServletWebRequest(requestAttr.getRequest(), requestAttr.getResponse());
}
@Override
public String toString() {
return "Current ServletWebRequest";
}
}
5.很明显，我们从getObject()中获取的值是从绑定当前线程的RequestAttribute中获取的,内部实现是通过ThreadLocal去完成的。看到这里，你应该明白了一点点。
private static final ThreadLocal requestAttributesHolder =
new NamedThreadLocal("Request attributes");
private static final ThreadLocal inheritableRequestAttributesHolder =
new NamedInheritableThreadLocal("Request context");
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;
}
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/DispatcherPortlet: " +
"In this case, use RequestContextListener or RequestContextFilter to expose the current request.");
}
}
return attributes;
}
public static RequestAttributes getRequestAttributes() {
RequestAttributes attributes = requestAttributesHolder.get();
if (attributes == null) {
attributes = inheritableRequestAttributesHolder.get();
}
return attributes;
}
6.我们再来捋一捋@Autowired注入HttpServletRequest对象的过程。这里以HttpServletRequest对象注入举例。首先调用DefaultListableBeanFactory中的findAutowireCandidates()方法，判断autowiringType类型是否和requiredType类型一致或者是autowiringType是否是requiredType的父接口(父类)。如果满足条件的话，我们会从resolvableDependencies中通过autowiringType（对应着上文的ServletRequest）拿到autowiringValue(对应着上文的RequestObjectFactory)。然后调用AutowireUtils.resolveAutowiringValue()对我们的ObjectFactory进行处理。
protected Map findAutowireCandidates(
String beanName, Class requiredType, DependencyDescriptor descriptor) {
String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this, requiredType, true, descriptor.isEager());
Map result = new LinkedHashMap(candidateNames.length);
for (Class autowiringType : this.resolvableDependencies.keySet()) {
if (autowiringType.isAssignableFrom(requiredType)) {
Object autowiringValue = this.resolvableDependencies.get(autowiringType);
autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);
if (requiredType.isInstance(autowiringValue)) {
result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);
break;
}
}
}
for (String candidate : candidateNames) {
if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, descriptor)) {
addCandidateEntry(result, candidate, descriptor, requiredType);
}
}
if (result.isEmpty() && !indicatesMultipleBeans(requiredType)) {
// Consider fallback matches if the first pass failed to find anything...
DependencyDescriptor fallbackDescriptor = descriptor.forFallbackMatch();
for (String candidate : candidateNames) {
if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, fallbackDescriptor)) {
addCandidateEntry(result, candidate, descriptor, requiredType);
}
}
if (result.isEmpty()) {
// Consider self references as a final pass...
// but in the case of a dependency collection, not the very same bean itself.
for (String candidate : candidateNames) {
if (isSelfReference(beanName, candidate) &&
(!(descriptor instanceof MultiElementDescriptor) || !beanName.equals(candidate)) &&
isAutowireCandidate(candidate, fallbackDescriptor)) {
addCandidateEntry(result, candidate, descriptor, requiredType);
}
}
}
}
return result;
}
- 很明显，对我们的RequestObjectFactory进行了JDK动态代理。原来我们通过@Autowired注入拿到的HttpServletRequest对象是代理对象。
public static Object resolveAutowiringValue(Object autowiringValue, Class requiredType) {
if (autowiringValue instanceof ObjectFactory && !requiredType.isInstance(autowiringValue)) {
ObjectFactory factory = (ObjectFactory) autowiringValue;
if (autowiringValue instanceof Serializable && requiredType.isInterface()) {
autowiringValue = Proxy.newProxyInstance(requiredType.getClassLoader(),
new Class[] {requiredType}, new ObjectFactoryDelegatingInvocationHandler(factory));
}
else {
return factory.getObject();
}
}
return autowiringValue;
}
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();
}
}
}
8.我们再来看SpringMVC是怎么把HttpServletRequest对象放入到ThreadLocal中。当用户发出请求后，会经过FrameworkServlet中的processRequest()方法做了一些骚操作，然后再交给子类DispatcherServlet中的doService()去处理这个请求。这些骚操作就包括把request,response对象包装成ServletRequestAttributes对象，然后放入到ThreadLocal中。
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 ex) {
failureCause = ex;
throw ex;
}
catch (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();
}
if (logger.isDebugEnabled()) {
if (failureCause != null) {
this.logger.debug("Could not complete request", failureCause);
}
else {
if (asyncManager.isConcurrentHandlingStarted()) {
logger.debug("Leaving response open for concurrent processing");
}
else {
this.logger.debug("Successfully completed request");
}
}
}
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
- buildRequestAttributes()方法将当前request和response对象包装成ServletRequestAttributes对象。initContextHolders()负责把RequestAttributes对象放入到requestAttributesHolder(ThreadLocal)中。一切真相大白。
protected ServletRequestAttributes buildRequestAttributes(
HttpServletRequest request, HttpServletResponse response, RequestAttributes previousAttributes) {
if (previousAttributes == null || previousAttributes instanceof ServletRequestAttributes) {
return new ServletRequestAttributes(request, response);
}
else {
return null; // preserve the pre-bound RequestAttributes instance
}
}
private void initContextHolders(
HttpServletRequest request, LocaleContext localeContext, RequestAttributes requestAttributes) {
if (localeContext != null) {
LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);
}
if (requestAttributes != null) {
RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);
}
if (logger.isTraceEnabled()) {
logger.trace("Bound request context to thread: " + request);
}
}
public static void setRequestAttributes(RequestAttributes attributes, boolean inheritable) {
if (attributes == null) {
resetRequestAttributes();
}
else {
if (inheritable) {
inheritableRequestAttributesHolder.set(attributes);
requestAttributesHolder.remove();
}
else {
requestAttributesHolder.set(attributes);
inheritableRequestAttributesHolder.remove();
}
}
}
private static final boolean jsfPresent =
ClassUtils.isPresent("javax.faces.context.FacesContext", RequestContextHolder.class.getClassLoader());
private static final ThreadLocal requestAttributesHolder =
new NamedThreadLocal("Request attributes");
private static final ThreadLocal inheritableRequestAttributesHolder =
new NamedInheritableThreadLocal("Request context");
- SpringMVC会优先执行被@ModelAttribute注解的方法。也就是说我们每一次请求，都会去调用init()方法，对request，response，httpSession进行赋值操作，并发问题也由此产生。
private void invokeModelAttributeMethods(NativeWebRequest request, ModelAndViewContainer container)
throws Exception {
while (!this.modelMethods.isEmpty()) {
InvocableHandlerMethod modelMethod = getNextModelMethod(container).getHandlerMethod();
ModelAttribute ann = modelMethod.getMethodAnnotation(ModelAttribute.class);
if (container.containsAttribute(ann.name())) {
if (!ann.binding()) {
container.setBindingDisabled(ann.name());
}
continue;
}
Object returnValue = modelMethod.invokeForRequest(request, container);
if (!modelMethod.isVoid()){
String returnValueName = getNameForReturnValue(returnValue, modelMethod.getReturnType());
if (!ann.binding()) {
container.setBindingDisabled(returnValueName);
}
if (!container.containsAttribute(returnValueName)) {
container.addAttribute(returnValueName, returnValue);
}
}
}
}
public abstract class BaseController1 {
protected HttpServletRequest request;
protected HttpServletResponse response;
protected HttpSession httpSession;
@ModelAttribute
public void init(HttpServletRequest request,
HttpServletResponse response,
HttpSession httpSession) {
this.request = request;
this.response = response;
this.httpSession = httpSession;
}
}
2019-04-18更新
最近的面试，让我想到了3个问题。假如有2个请求过来，一个是A请求，一个是B请求。A请求和B请求所处于不同线程(Spring中的Controller是单例多线程，也可以Controller的作用域设置为prototype，这样每次请求过来都会生成一个新的实例，不存在多线程问题，但同时也带来了更大的内存消耗，Struts2就是这样做的)，这时候会出现以下情况：
- 1.A请求和B请求的HttpServletRequest对象都是ThreadLocal(
@Autowire方式最终调用RequestContextHolder.currentRequestAttributes().getRequest())中获取到的。Tomcat的处理模型是Connector+Executor，最终是Executor复用线程来处理实际的业务。有没有可能会出现这种情况：A请求所在线程是A。当A请求结束后，B请求复用线程A，此时拿到的HttpServletRequest对象其实是A的。 其实仔细想一想就觉得不可能，当A请求完成时，应该会调用ThreadLocal.remove()方法清除线程A中绑定的HttpServletRequest对象。可以在RequestContextFilter看到一些猫腻！
RequestContextFilter.png
- 2.我们的每次请求，Tomcat中的Executor都会分配一个线程来进行处理。每次请求都会创建HttpServletRequest 和 HttpServletResponse对象。正因为Controller是单例多线程，上述通过@ModelAndView方法初始化HttpServletRequest对象，会造成HttpServletRequest覆盖问题(后一次的请求覆盖前一次的请求)。对于在同一个Controller，为什么每次请求中的HttpServletRequest对象的hashCode都相同？因为HttpServletRequest是通过@Autowire注入来的，Controller中的HttpServletRequest实际上不是RequestFacade对象，而是Proxy(代理RequestObjectFactory)对象。所以这里的hashCode其实是Proxy对象在内存中的地址，真相大白！
AutowireUtils.png
- 3.以方法参数注入的HttpServletRequest是没有线程安全问题的。但是我们在网页上请求
/4接口100次，此时httpServletRequest对象的hashCode是一样的，这是为什么呢？服务器中每个thread所申请的request的内存空间在这个服务器启动的时候就是固定的，那么我每次请求，它都会在它所申请到的内存空间（可能是类似数组这样的结构）中新建一个request,（类似于数组的起点总是同一个内存地址）。那么我发起一个请求，他就会在起始位置新建一个Request传递给Servlet并开始处理，处理结束后就会销毁，那么他下一个请求所新建的Request。因为之前的request销毁了，所以又从起始地址开始创建，这样一切就解释得通了。
image.png
我们先请求/4，再请求/5。两次请求中的HttpServletRequest的hashCode肯定不一样，因为/4处于阻塞状态，其HttpServletRequest不能被成功销毁。'/5'请求中的HttpServletRequest不能占据以前的内存地址，遂导致2次请求中的HttpServletRequest的hashCode不一致。
image.png
/4.png
/5.png
尾言
大家好，我是cmazxiaoma(寓意是沉梦昂志的小马)，希望和你们一起成长进步，感谢各位阅读本文章。
小弟不才。
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