MVC Handler Interceptors: Learn how to intercept HTTP requests on Java Spring

507se
507se
Jun 20, 2020 · 5 min read
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What is an MVC handler interceptor and why should you use it?

Setup for the interceptor class

Setting up handler interceptor

public class MyCustomHandlerInterceptor extends HandlerInterceptorAdapter {    @Override
public boolean preHandle(
HttpServletRequest request,
HttpServletResponse response,
Object handler) {
return true;
}
@Override
public void postHandle(
HttpServletRequest request,
HttpServletResponse response,
Object handler,
ModelAndView modelAndView) {

}
}

Data flow

@Bean
public MyCustomHandlerInterceptor myCustomHandlerInterceptor() {
return new MyCustomHandlerInterceptor();
}
@Bean
public WebMvcConfigurerAdapter adapter() {
return new WebMvcConfigurerAdapter() {
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(myCustomHandlerInterceptor());
}
};
}

Use cases

Retrieving HTTP Headers

@Override
public boolean preHandle(
HttpServletRequest request,
HttpServletResponse response,
Object handler) {
String myHeader = request.getHeader("MY_HTTP_HEADER");
// Processing happens here...
return true;
}

Leveraging attributes

@Override
public boolean preHandle(
HttpServletRequest request,
HttpServletResponse response,
Object handler) {
request.setAttribute(
"startTime",
System.currentTimeMillis()
);

// Processing happens here...
return true;
}
@Override
public void postHandle(
HttpServletRequest request,
HttpServletResponse response,
Object handler,
ModelAndView modelAndView) {
long startTime = (long)request.getAttribute("startTime");
// Processing happens here...
}

Status Code

@Override
public boolean preHandle(
HttpServletRequest request,
HttpServletResponse response,
Object handler) {

// Processing happens here...
response.setStatus(HttpStatus.UNAUTHORIZED.value());
return false;
}

Path

@Override
public boolean preHandle(
HttpServletRequest request,
HttpServletResponse response,
Object handler) {

if (request.getServletPath().contains("/auth")) {
// Processing happens here...
}
return true;
}

Docs

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