Spring Boot：拦截器 preHandle 运行 在流端点上两次
SpringBoot: Interceptor's preHandle run twice on streaming endpoint
我想使用拦截器来管理与服务器的当前活动连接数。除了通常的 JSON 端点外，我的 API 还提供流字节的端点。我实现了一个会话管理器，它跟踪会话计数、一个限制性拦截器和几个 API 端点。下面是一些示例代码。
通常的 JSON 端点与拦截器 运行 很好。然而，流端点实际上调用拦截器的 preHandle 方法两次，但 afterCompletion 只调用一次。对 preHandle 的第二次调用发生在第一次调用的响应计算完成之后。当我从拦截器中删除会话管理器时，此行为不再发生。
最小工作示例：
配置：
@Configuration
@RequiredArgsConstructor
public class AppConfig implements WebMvcConfigurer {
private final Interceptor interceptor;
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(this.interceptor).addPathPatterns("/numbers", "/numbers/*");
}
}
拦截器：
@Component
@RequiredArgsConstructor
@Slf4j
public class Interceptor implements HandlerInterceptor {
private final SessionManager sessionManager;
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
log.info("Pre-handle {}", this.hashCode());
return this.sessionManager.accept();
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception e) {
log.info("After completion {}", this.hashCode());
this.sessionManager.leave();
}
}
会话管理员：
@Component
@Slf4j
public class SessionManager {
private static final int MAX_SESSION_COUNT = 1;
private final AtomicInteger sessionCount = new AtomicInteger(0);
public synchronized boolean accept() {
int sessionCount = this.sessionCount.get();
if (sessionCount >= MAX_SESSION_COUNT) {
log.error("Upper session limit hit! Currently active sessions: {}, maximum allowed active sessions: {}", sessionCount, MAX_SESSION_COUNT);
return false;
}
sessionCount = this.sessionCount.incrementAndGet();
log.debug("Accept new session. Currently active sessions: {}, maximum allowed active sessions: {}", sessionCount, MAX_SESSION_COUNT);
return true;
}
public void leave() {
int sessionCount = this.sessionCount.decrementAndGet();
log.debug("Decrement session count to {}", sessionCount);
}
}
控制器：
@RestController
@RequestMapping("/numbers")
@Slf4j
public class Controller {
private final Random random = new Random();
@PostMapping("")
public ResponseEntity<List<Integer>> number() {
log.info("Generate numbers");
List<Integer> bytes = IntStream.range(0, 1_000)
.map(ignored -> this.random.nextInt(255))
.boxed()
.collect(Collectors.toList());
return ResponseEntity.ok(bytes);
}
@PostMapping("/stream")
public ResponseEntity<StreamingResponseBody> numberStream() {
log.info("Generate stream start");
StreamingResponseBody responseBody = outputStream -> {
for (int i = 0; i < 1_000_000; i++) {
outputStream.write(this.random.nextInt(255));
}
};
return ResponseEntity.ok()
.contentType(MediaType.APPLICATION_OCTET_STREAM)
.body(responseBody);
}
}
我找到了 a similar topic on Whosebug，但是那里给出的建议对我来说不起作用。从我的拦截器中删除 @Component 并在 addInterceptors 方法中手动实例化拦截器和会话管理器时，行为不会改变。
日志（最大会话数 = 2）：
. ____ _ __ _ _
/\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.6.1)
2021-12-10 14:21:25.999 INFO 17112 --- [ main] c.e.untitled2.Untitled2Application : Starting Untitled2Application using Java 1.8.0_312 on HOSTNAME with PID 17112 (D:\IntelliJProjects\untitled2\target\classes started by USERNAME in D:\IntelliJProjects\untitled2)
2021-12-10 14:21:26.001 INFO 17112 --- [ main] c.e.untitled2.Untitled2Application : No active profile set, falling back to default profiles: default
2021-12-10 14:21:26.626 INFO 17112 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2021-12-10 14:21:26.632 INFO 17112 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2021-12-10 14:21:26.632 INFO 17112 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.55]
2021-12-10 14:21:26.701 INFO 17112 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2021-12-10 14:21:26.701 INFO 17112 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 669 ms
2021-12-10 14:21:26.907 INFO 17112 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2021-12-10 14:21:26.913 INFO 17112 --- [ main] c.e.untitled2.Untitled2Application : Started Untitled2Application in 1.197 seconds (JVM running for 1.84)
#### Call /numbers
2021-12-10 14:21:49.494 INFO 17112 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-12-10 14:21:49.494 INFO 17112 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2021-12-10 14:21:49.494 INFO 17112 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 0 ms
2021-12-10 14:21:49.502 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers
2021-12-10 14:21:49.503 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 1, maximum allowed active sessions: 2
2021-12-10 14:21:49.508 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.Controller : Generate numbers
2021-12-10 14:21:49.536 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.Interceptor : After completion 1184674729
2021-12-10 14:21:49.536 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.SessionManager : Decrement session count to 0
#### Call /numbers again
2021-12-10 14:21:57.054 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers
2021-12-10 14:21:57.054 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 1, maximum allowed active sessions: 2
2021-12-10 14:21:57.054 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.Controller : Generate numbers
2021-12-10 14:21:57.055 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.Interceptor : After completion 1184674729
2021-12-10 14:21:57.055 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.SessionManager : Decrement session count to 0
#### Call /numbers/stream
2021-12-10 14:22:06.375 INFO 17112 --- [nio-8080-exec-4] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers/stream
2021-12-10 14:22:06.376 INFO 17112 --- [nio-8080-exec-4] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 1, maximum allowed active sessions: 2
2021-12-10 14:22:06.376 INFO 17112 --- [nio-8080-exec-4] com.example.untitled2.Controller : Generate stream start
2021-12-10 14:22:06.414 INFO 17112 --- [nio-8080-exec-5] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 317286159: POST /numbers/stream
2021-12-10 14:22:06.414 INFO 17112 --- [nio-8080-exec-5] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 2, maximum allowed active sessions: 2
2021-12-10 14:22:06.416 INFO 17112 --- [nio-8080-exec-5] com.example.untitled2.Interceptor : After completion 1184674729
2021-12-10 14:22:06.416 INFO 17112 --- [nio-8080-exec-5] com.example.untitled2.SessionManager : Decrement session count to 1
#### Call /numbers/stream again
2021-12-10 14:22:17.857 INFO 17112 --- [nio-8080-exec-6] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers/stream
2021-12-10 14:22:17.857 INFO 17112 --- [nio-8080-exec-6] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 2, maximum allowed active sessions: 2
2021-12-10 14:22:17.857 INFO 17112 --- [nio-8080-exec-6] com.example.untitled2.Controller : Generate stream start
2021-12-10 14:22:17.889 INFO 17112 --- [nio-8080-exec-7] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1473864520: POST /numbers/stream
2021-12-10 14:22:17.889 ERROR 17112 --- [nio-8080-exec-7] com.example.untitled2.SessionManager : Upper session limit hit! Currently active sessions: 2, maximum allowed active sessions: 2
#### Call /numbers/stream again
2021-12-10 14:22:26.443 INFO 17112 --- [nio-8080-exec-8] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers/stream
2021-12-10 14:22:26.443 ERROR 17112 --- [nio-8080-exec-8] com.example.untitled2.SessionManager : Upper session limit hit! Currently active sessions: 2, maximum allowed active sessions: 2
日志显示 preHandle 被调用了两次，而 afterCompletion 只被调用了一次。
来自document
Note: Will only be called if this interceptor's preHandle method has successfully completed and returned true!
afterCompletion()方法只有在preHandle()方法returnstrue时才会被调用。在您的情况下，您正在增加会话计数并返回 false。
如果您想始终调用 sessionManager.leave();（无论 preHandle() returns 是什么），请使用 postHandle() 而不是 afterCompletion()。
因此，为了解决您遇到的问题，我们需要从 Servlet 环境支持的调度类型开始，尤其是作为 Servlet 3.0 规范的一部分添加的 ASYNC 调度类型。简而言之，添加了 ASYNC 调度类型以支持长 运行 / 重请求，这些请求在过去会阻止 servlet 容器处理其他请求，因为处理程序线程被阻塞等待 heavy/long-running要完成的任务。所以聪明的人决定可以在并行线程中执行长 运行 和繁重的作业，并且可以将主工作线程释放到池中，以便可以处理新的小请求。
让我们回到您的问题：
因此，有两个端点，一个是 returning JSON 或一个可以由处理程序线程处理的简单对象，另一个是 return 是 StreamingResponseBody。对于第一个，没有定义特殊处理，因此 Spring 将请求作为普通请求处理，只生成一个有效负载，然后 return 将其返回给客户端。对于第二个 spring 有一个名为 StreamingResponseBodyReturnValueHandler 的自定义响应处理程序，它基本上创建请求的异步版本（处理所有属性但更改调度类型）并通过将执行推送到新线程WebAsyncManager.
那么为什么 preHandle() 调用了两次？那是因为一旦它作为基于 REQUEST 调度的第一次执行的一部分被调用并且就在预句柄 Spring 开始处理请求并理解它应该在 ASYNC 模式下处理因为 return 类型是一个流（基本上没有大小的东西），所以请求的副本被制作它再次在新线程中执行。因此，如果您查看 preHandle()，您会注意到它是从不同的线程调用的，具有相同的请求数据，但请求时的调度类型不同。
更多信息在这里：
那你能做什么？
你的 Interceptor 应该有点聪明，不要盲目地调用 sessionManager.accept(); 而是检查请求是否已经被处理过。
所以非常虚拟的版本看起来像这样
@Component
@RequiredArgsConstructor
@Slf4j
public class Interceptor implements HandlerInterceptor {
private final SessionManager sessionManager;
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
log.info("Pre-handle {}", this.hashCode());
if(BooleanUtils.isTrue(request.getAttribute("accepted")) || DispatcherType.ASYNC == request.getDispatcherType()){
return true;
}
boolean accepted = this.sessionManager.accept();
if (accepted){
request.setAttribute("accepted", true);
}
return accepted;
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception e) {
log.info("After completion {}", this.hashCode());
this.sessionManager.leave();
}
}
我想使用拦截器来管理与服务器的当前活动连接数。除了通常的 JSON 端点外，我的 API 还提供流字节的端点。我实现了一个会话管理器，它跟踪会话计数、一个限制性拦截器和几个 API 端点。下面是一些示例代码。
通常的 JSON 端点与拦截器 运行 很好。然而，流端点实际上调用拦截器的 preHandle 方法两次，但 afterCompletion 只调用一次。对 preHandle 的第二次调用发生在第一次调用的响应计算完成之后。当我从拦截器中删除会话管理器时，此行为不再发生。
最小工作示例：
配置：
@Configuration
@RequiredArgsConstructor
public class AppConfig implements WebMvcConfigurer {
private final Interceptor interceptor;
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(this.interceptor).addPathPatterns("/numbers", "/numbers/*");
}
}
拦截器：
@Component
@RequiredArgsConstructor
@Slf4j
public class Interceptor implements HandlerInterceptor {
private final SessionManager sessionManager;
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
log.info("Pre-handle {}", this.hashCode());
return this.sessionManager.accept();
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception e) {
log.info("After completion {}", this.hashCode());
this.sessionManager.leave();
}
}
会话管理员：
@Component
@Slf4j
public class SessionManager {
private static final int MAX_SESSION_COUNT = 1;
private final AtomicInteger sessionCount = new AtomicInteger(0);
public synchronized boolean accept() {
int sessionCount = this.sessionCount.get();
if (sessionCount >= MAX_SESSION_COUNT) {
log.error("Upper session limit hit! Currently active sessions: {}, maximum allowed active sessions: {}", sessionCount, MAX_SESSION_COUNT);
return false;
}
sessionCount = this.sessionCount.incrementAndGet();
log.debug("Accept new session. Currently active sessions: {}, maximum allowed active sessions: {}", sessionCount, MAX_SESSION_COUNT);
return true;
}
public void leave() {
int sessionCount = this.sessionCount.decrementAndGet();
log.debug("Decrement session count to {}", sessionCount);
}
}
控制器：
@RestController
@RequestMapping("/numbers")
@Slf4j
public class Controller {
private final Random random = new Random();
@PostMapping("")
public ResponseEntity<List<Integer>> number() {
log.info("Generate numbers");
List<Integer> bytes = IntStream.range(0, 1_000)
.map(ignored -> this.random.nextInt(255))
.boxed()
.collect(Collectors.toList());
return ResponseEntity.ok(bytes);
}
@PostMapping("/stream")
public ResponseEntity<StreamingResponseBody> numberStream() {
log.info("Generate stream start");
StreamingResponseBody responseBody = outputStream -> {
for (int i = 0; i < 1_000_000; i++) {
outputStream.write(this.random.nextInt(255));
}
};
return ResponseEntity.ok()
.contentType(MediaType.APPLICATION_OCTET_STREAM)
.body(responseBody);
}
}
我找到了 a similar topic on Whosebug，但是那里给出的建议对我来说不起作用。从我的拦截器中删除 @Component 并在 addInterceptors 方法中手动实例化拦截器和会话管理器时，行为不会改变。
日志（最大会话数 = 2）：
. ____ _ __ _ _
/\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.6.1)
2021-12-10 14:21:25.999 INFO 17112 --- [ main] c.e.untitled2.Untitled2Application : Starting Untitled2Application using Java 1.8.0_312 on HOSTNAME with PID 17112 (D:\IntelliJProjects\untitled2\target\classes started by USERNAME in D:\IntelliJProjects\untitled2)
2021-12-10 14:21:26.001 INFO 17112 --- [ main] c.e.untitled2.Untitled2Application : No active profile set, falling back to default profiles: default
2021-12-10 14:21:26.626 INFO 17112 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2021-12-10 14:21:26.632 INFO 17112 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2021-12-10 14:21:26.632 INFO 17112 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.55]
2021-12-10 14:21:26.701 INFO 17112 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2021-12-10 14:21:26.701 INFO 17112 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 669 ms
2021-12-10 14:21:26.907 INFO 17112 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2021-12-10 14:21:26.913 INFO 17112 --- [ main] c.e.untitled2.Untitled2Application : Started Untitled2Application in 1.197 seconds (JVM running for 1.84)
#### Call /numbers
2021-12-10 14:21:49.494 INFO 17112 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-12-10 14:21:49.494 INFO 17112 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2021-12-10 14:21:49.494 INFO 17112 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 0 ms
2021-12-10 14:21:49.502 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers
2021-12-10 14:21:49.503 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 1, maximum allowed active sessions: 2
2021-12-10 14:21:49.508 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.Controller : Generate numbers
2021-12-10 14:21:49.536 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.Interceptor : After completion 1184674729
2021-12-10 14:21:49.536 INFO 17112 --- [nio-8080-exec-1] com.example.untitled2.SessionManager : Decrement session count to 0
#### Call /numbers again
2021-12-10 14:21:57.054 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers
2021-12-10 14:21:57.054 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 1, maximum allowed active sessions: 2
2021-12-10 14:21:57.054 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.Controller : Generate numbers
2021-12-10 14:21:57.055 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.Interceptor : After completion 1184674729
2021-12-10 14:21:57.055 INFO 17112 --- [nio-8080-exec-3] com.example.untitled2.SessionManager : Decrement session count to 0
#### Call /numbers/stream
2021-12-10 14:22:06.375 INFO 17112 --- [nio-8080-exec-4] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers/stream
2021-12-10 14:22:06.376 INFO 17112 --- [nio-8080-exec-4] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 1, maximum allowed active sessions: 2
2021-12-10 14:22:06.376 INFO 17112 --- [nio-8080-exec-4] com.example.untitled2.Controller : Generate stream start
2021-12-10 14:22:06.414 INFO 17112 --- [nio-8080-exec-5] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 317286159: POST /numbers/stream
2021-12-10 14:22:06.414 INFO 17112 --- [nio-8080-exec-5] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 2, maximum allowed active sessions: 2
2021-12-10 14:22:06.416 INFO 17112 --- [nio-8080-exec-5] com.example.untitled2.Interceptor : After completion 1184674729
2021-12-10 14:22:06.416 INFO 17112 --- [nio-8080-exec-5] com.example.untitled2.SessionManager : Decrement session count to 1
#### Call /numbers/stream again
2021-12-10 14:22:17.857 INFO 17112 --- [nio-8080-exec-6] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers/stream
2021-12-10 14:22:17.857 INFO 17112 --- [nio-8080-exec-6] com.example.untitled2.SessionManager : Accept new session. Currently active sessions: 2, maximum allowed active sessions: 2
2021-12-10 14:22:17.857 INFO 17112 --- [nio-8080-exec-6] com.example.untitled2.Controller : Generate stream start
2021-12-10 14:22:17.889 INFO 17112 --- [nio-8080-exec-7] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1473864520: POST /numbers/stream
2021-12-10 14:22:17.889 ERROR 17112 --- [nio-8080-exec-7] com.example.untitled2.SessionManager : Upper session limit hit! Currently active sessions: 2, maximum allowed active sessions: 2
#### Call /numbers/stream again
2021-12-10 14:22:26.443 INFO 17112 --- [nio-8080-exec-8] com.example.untitled2.Interceptor : Interceptor 1184674729 pre-handles request 1068123396: POST /numbers/stream
2021-12-10 14:22:26.443 ERROR 17112 --- [nio-8080-exec-8] com.example.untitled2.SessionManager : Upper session limit hit! Currently active sessions: 2, maximum allowed active sessions: 2
日志显示 preHandle 被调用了两次，而 afterCompletion 只被调用了一次。
来自document
Note: Will only be called if this interceptor's preHandle method has successfully completed and returned true!
afterCompletion()方法只有在preHandle()方法returnstrue时才会被调用。在您的情况下，您正在增加会话计数并返回 false。
如果您想始终调用 sessionManager.leave();（无论 preHandle() returns 是什么），请使用 postHandle() 而不是 afterCompletion()。
因此，为了解决您遇到的问题，我们需要从 Servlet 环境支持的调度类型开始，尤其是作为 Servlet 3.0 规范的一部分添加的 ASYNC 调度类型。简而言之，添加了 ASYNC 调度类型以支持长 运行 / 重请求，这些请求在过去会阻止 servlet 容器处理其他请求，因为处理程序线程被阻塞等待 heavy/long-running要完成的任务。所以聪明的人决定可以在并行线程中执行长 运行 和繁重的作业，并且可以将主工作线程释放到池中，以便可以处理新的小请求。
让我们回到您的问题：
因此，有两个端点，一个是 returning JSON 或一个可以由处理程序线程处理的简单对象，另一个是 return 是 StreamingResponseBody。对于第一个，没有定义特殊处理，因此 Spring 将请求作为普通请求处理，只生成一个有效负载，然后 return 将其返回给客户端。对于第二个 spring 有一个名为 StreamingResponseBodyReturnValueHandler 的自定义响应处理程序，它基本上创建请求的异步版本（处理所有属性但更改调度类型）并通过将执行推送到新线程WebAsyncManager.
那么为什么 preHandle() 调用了两次？那是因为一旦它作为基于 REQUEST 调度的第一次执行的一部分被调用并且就在预句柄 Spring 开始处理请求并理解它应该在 ASYNC 模式下处理因为 return 类型是一个流（基本上没有大小的东西），所以请求的副本被制作它再次在新线程中执行。因此，如果您查看 preHandle()，您会注意到它是从不同的线程调用的，具有相同的请求数据，但请求时的调度类型不同。
更多信息在这里：
那你能做什么？
你的 Interceptor 应该有点聪明，不要盲目地调用 sessionManager.accept(); 而是检查请求是否已经被处理过。
所以非常虚拟的版本看起来像这样
@Component
@RequiredArgsConstructor
@Slf4j
public class Interceptor implements HandlerInterceptor {
private final SessionManager sessionManager;
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
log.info("Pre-handle {}", this.hashCode());
if(BooleanUtils.isTrue(request.getAttribute("accepted")) || DispatcherType.ASYNC == request.getDispatcherType()){
return true;
}
boolean accepted = this.sessionManager.accept();
if (accepted){
request.setAttribute("accepted", true);
}
return accepted;
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception e) {
log.info("After completion {}", this.hashCode());
this.sessionManager.leave();
}
}