In this article, we will introduce the interceptors in SpringBoot in detail, including the concept, function, implementation, execution sequence, life cycle and advanced application of interceptors. Finally, we will also explore performance optimization strategies and common problems for interceptors.
1. The concept and function of interceptor
1.1 What is an interceptor
Interceptor is a special component that can intercept and process requests and responses during request processing. Interceptors can perform specific actions before the request reaches the target handler, after the handler processes the request, and before the view is rendered. The main purpose of the interceptor is to achieve unified processing of requests and responses without modifying the original code.
1.2 The role of interceptors
Interceptors can be used to implement the following functions:
- Permission control: The interceptor can perform permission verification before the request reaches the processor, so as to achieve access control for different users.
- Logging: The interceptor can record the detailed information of the request and response during the request processing, which is convenient for later analysis and debugging.
- Interface idempotence check: The interceptor can perform idempotency check before the request reaches the processor to prevent repeated submission.
- Data verification: The interceptor can verify the request data before the request reaches the processor to ensure the legality of the data.
- Cache processing: Interceptors can cache response data after request processing to improve system performance.
1.3 The difference between interceptors and filters
Both interceptors and filters can intercept and process requests and responses, but there are the following differences between them:
- Execution order: Filters are executed before interceptors, and interceptors are executed before processors.
- Functional scope: Filters can intercept all requests, while interceptors can only intercept specific requests.
- Lifecycle: Filters are managed by the Servlet container, and interceptors are managed by the Spring container.
- Usage scenario: Filters are suitable for global processing of requests and responses, and interceptors are suitable for processing specific requests.
2. Interceptor implementation in SpringBoot
2.1 Implement the HandlerInterceptor interface
To implement an interceptor in SpringBoot, you first need to create a class and implement the HandlerInterceptor interface. The HandlerInterceptor interface contains the following three methods:
- preHandle: Executed before the request reaches the processor, which can be used for authorization verification, data verification and other operations. If it returns true, continue to perform subsequent operations; if it returns false, interrupt request processing.
- postHandle: Executed after the processor processes the request, it can be used for logging, cache processing and other operations.
- afterCompletion: Executed before the view is rendered, and can be used for resource cleanup and other operations.
Here is an example of a simple interceptor implementation:
public class MyInterceptor implements HandlerInterceptor {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
System.out.println("preHandle: " + request.getRequestURI());
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) {
System.out.println("postHandle: " + request.getRequestURI());
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
System.out.println("afterCompletion: " + request.getRequestURI());
}
}
2.2 Register the interceptor to InterceptorRegistry
For an interceptor to take effect, it needs to be registered in the InterceptorRegistry. This can be achieved by implementing the WebMvcConfigurer interface and overriding the addInterceptors method. Here is a simple registration example:
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(new MyInterceptor());
}
}
2.3 Configure the interception rules of the interceptor
When registering an interceptor, you can configure the interceptor's interception rules through the addPathPatterns and excludePathPatterns methods. The addPathPatterns method is used to specify the request paths that need to be intercepted, and the excludePathPatterns method is used to specify the request paths that do not need to be intercepted. Here is an example configuration:
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(new MyInterceptor())
.addPathPatterns("/**")
.excludePathPatterns("/login", "/register");
}
}
In the above example, we configured the interceptor to intercept all requests except login and registration requests.
3. Execution sequence and life cycle of interceptors
3.1 Execution order of interceptors
When there are multiple interceptors, their execution order depends on the registration order. The interceptor registered first is executed first, and the interceptor registered later is executed later. During request processing, the preHandle method of the interceptor is executed in the registration order, while the postHandle and afterCompletion methods are executed in the reverse order of the registration order.
3.2 Interceptor life cycle
The lifecycle of interceptors is managed by the Spring container. When the Spring container starts, the interceptor will be instantiated and initialized; when the Spring container is shut down, the interceptor will be destroyed.
3.3 Execution process of multiple interceptors
When there are multiple interceptors, their execution flow is as follows:
- Execute the preHandle methods of all interceptors in the order of registration. If the preHandle method of an interceptor returns false, the request processing is interrupted and the afterCompletion method of the executed interceptor is directly executed.
- Execute the handler's processing method.
- Execute the postHandle methods of all interceptors in the reverse order of the registration order.
- Render the view.
- Execute the afterCompletion methods of all interceptors in the reverse order of the registration order.
4. Advanced applications of interceptors
4.1 Interceptor implements permission control
The interceptor can perform permission verification before the request reaches the processor, so as to realize access control to different users. The following is a simple permission control example:
public class AuthInterceptor implements HandlerInterceptor {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
HttpSession session = request.getSession();
User user = (User) session.getAttribute("user");
if (user == null) {
response.sendRedirect("/login");
return false;
}
return true;
}
}
In the above example, we check in the preHandle method if the user is logged in, and if not, redirect to the login page and interrupt the request processing.
4.2 Interceptor implements logging
The interceptor can record the detailed information of the request and response during request processing, which is convenient for later analysis and debugging. Here is a simple logging example:
public class LogInterceptor implements HandlerInterceptor {
private static final Logger logger = LoggerFactory.getLogger(LogInterceptor.class);
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
logger.info("Request URI: {}", request.getRequestURI());
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) {
logger.info("Response status: {}", response.getStatus());
}
}
In the above example, we log the request URI in the preHandle method and the response status in the postHandle method.
4.3 Interceptor implements interface idempotency check
The interceptor can perform idempotence checks before the request reaches the processor to prevent repeated submissions. The following is an example of a simple idempotence check:
public class IdempotentInterceptor implements HandlerInterceptor {
private static final String IDEMPOTENT_TOKEN = "idempotentToken";
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
String token = request.getHeader(IDEMPOTENT_TOKEN);
if (StringUtils.isEmpty(token)) {
throw new RuntimeException("Idempotent token is missing");
}
if (!checkIdempotentToken(token)) {
throw new RuntimeException("Duplicate request");
}
return true;
}
private boolean checkIdempotentToken(String token) {
// Check the token in the cache or database
// Return true if the token is valid, false otherwise
}
}
In the above example, we check the idempotency token in the request header in the preHandle method, and if the token is invalid, we throw an exception and interrupt the request processing.
5. Interceptor performance optimization and common problems
5.1 Interceptor performance optimization strategy
Interceptors may affect system performance during request processing. Here are some performance optimization strategies:
- Reduce the number of interceptors: Try to concentrate related functions into one interceptor to avoid creating too many interceptors.
- Precisely configure interception rules: precisely configure interception rules through addPathPatterns and excludePathPatterns methods to avoid unnecessary interception.
- Use asynchronous processing: Use asynchronous processing in the interceptor to avoid blocking the request processing process.
- Use cache: Use cache in interceptors to reduce access to databases or other resources.
5.2 Common problems and solutions for interceptors
An interceptor is a type of middleware for processing requests and responses, which can perform some actions before the request reaches the target processor or before the response returns to the client. However, in actual use, we may encounter some problems, such as interceptors not taking effect, executing in the wrong order or affecting performance, etc. Next, we will analyze the causes and solutions of these problems one by one.
- The interceptor does not take effect: There are many possible reasons why the interceptor does not take effect, the most common of which include the fact that the interceptor is not registered to the InterceptorRegistry, the configuration of the interception rules is incorrect, and so on. In order to solve this problem, we need to first check whether the interceptor has been correctly registered in the InterceptorRegistry, and then check whether the interception rules are configured correctly. If a problem is found, it needs to be adjusted and repaired in time.
- Wrong execution order of interceptors: The main reason for wrong execution order of interceptors is that the registration order of interceptors is wrong. In practical applications, the execution order of interceptors is determined according to the order in which they are registered in the InterceptorRegistry. Therefore, in order to solve this problem, we need to adjust the registration order of the interceptors in the InterceptorRegistry to ensure that they are executed in the expected order.
- Interceptors affect performance: The main reason why interceptors affect performance is that the processing logic in the interceptor is too complex or the resource consumption is too large. In order to solve this problem, we need to optimize the processing logic of the interceptor to minimize unnecessary calculation and resource consumption. At the same time, we can also consider using some performance monitoring tools, such as JProfiler, to monitor and analyze the performance of the interceptor in real time, so as to find performance bottlenecks and optimize them.
The interceptor may encounter some problems in practical applications, but as long as we can deeply understand its principles and mechanisms, we can find a suitable solution.
Summarize
This article introduces the interceptors in SpringBoot in detail, including the concept, function, implementation, execution sequence, life cycle and advanced application of interceptors. We also explore performance optimization strategies and common problems for interceptors. I hope this article can help you better understand and use interceptors in SpringBoot.
