Java http response http header

How to Set a Header on a Response with Spring 5

As always, the writeup is super practical and based on a simple application that can work with documents with a mix of encrypted and unencrypted fields.

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The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

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1. Overview

In this quick tutorial, we’ll explore the different ways of setting a header on a service response, either for non-reactive endpoints or APIs, using Spring 5’s WebFlux framework.

We can find further information about this framework in previous posts.

2. Headers for Non-Reactive Components

If we want to set headers on single responses, we can use HttpServletResponse or ResponseEntity objects.

In contrast, if our objective is to add a filter to all or multiple responses, we’ll need to configure a Filter.

2.1. Using HttpServletResponse

We simply have to add the HttpServletResponse object to our REST endpoint as an argument, and then use the addHeader() method:

@GetMapping("/http-servlet-response") public String usingHttpServletResponse(HttpServletResponse response)

As shown in the above example, we don’t have to return the response object.

2.2. Using ResponseEntity

In this case, we’ll use the BodyBuilder provided by the ResponseEntity class:

@GetMapping("/response-entity-builder-with-http-headers") public ResponseEntity usingResponseEntityBuilderAndHttpHeaders()

The HttpHeaders class offers plenty of convenience methods to set the most common headers.

We can see more examples illustrating these points in our Github repo.

2.3. Adding a Header for All Responses

Now let’s imagine we want to set a particular header to many of our endpoints.

Of course, it would be frustrating if we had to replicate the previous code on each mapping method.

A better approach to accomplishing this is by configuring a Filter in our service:

@WebFilter("/filter-response-header/*") public class AddResponseHeaderFilter implements Filter < @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException < HttpServletResponse httpServletResponse = (HttpServletResponse) response; httpServletResponse.setHeader( "Baeldung-Example-Filter-Header", "Value-Filter"); chain.doFilter(request, response); >@Override public void init(FilterConfig filterConfig) throws ServletException < // . >@Override public void destroy() < // . >>

The @WebFilter annotation allows us to indicate the urlPatterns for which this Filter will become effective.

As we pointed out in this article, in order to make our Filter discoverable by Spring, we need to add the @ServletComponentScan annotation to our Spring Application class:

@ServletComponentScan @SpringBootApplication public class ResponseHeadersApplication < public static void main(String[] args) < SpringApplication.run(ResponseHeadersApplication.class, args); >>

If we don’t need any of the functionality provided by @WebFilter, we can avoid this last step by using the @Component annotation in our Filter class instead.

3. Headers for Reactive Endpoints

In this section, we’ll learn how to set headers on single endpoint responses using ServerHttpResponse, ResponseEntity or ServerResponse (for functional endpoints) classes and interfaces.

We’ll also discuss how to implement a Spring 5 WebFilter to add a header on all of our responses.

3.1. Using ServerHttpResponse

This approach is fairly similar to the HttpServletResponse counterpart:

@GetMapping("/server-http-response") public Mono usingServerHttpResponse(ServerHttpResponse response)

3.2. Using ResponseEntity

We can use the ResponseEntity class exactly as we do for non-reactive endpoints:

@GetMapping("/response-entity") public Mono> usingResponseEntityBuilder()

3.3. Using ServerResponse

The classes and interfaces introduced in the last two sub-sections can be used in @Controller annotated classes, but aren’t suitable for the new Spring 5 Functional Web Framework.

If we want to set a header on a HandlerFunction, then we’ll need to get our hands on the ServerResponse interface:

public Mono useHandler(final ServerRequest request)

3.4. Adding a Header for All Responses

Finally, Spring 5 provides a WebFilter interface to set a header on all the responses retrieved by a service:

@Component public class AddResponseHeaderWebFilter implements WebFilter < @Override public Monofilter(ServerWebExchange exchange, WebFilterChain chain) < exchange.getResponse() .getHeaders() .add("Baeldung-Example-Filter-Header", "Value-Filter"); return chain.filter(exchange); >>

4. Conclusion

In this article, we learned many different ways of setting a header on a response. Now whether we want to set it on a single endpoint, configure all our rest APIs, or even migrate to the reactive stack, we have the knowledge necessary.

As always, all the examples can be accessed in our Github repository, both the non-reactive ones and those using Spring 5 specific functionality.

Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.

The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:

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HTTP Response Header Retrieval: Simple Way to Get HTTP Response Header in Java – conn. getHeaderFields()

In Java, it is often necessary to retrieve the HTTP response header when working with APIs or web services. The HTTP response header contains important information about the response, such as the content type, encoding, and response code. In this blog post, we will explore a simple way to get the HTTP response header in Java.

Java provides a built-in class called HttpURLConnection, which is used to establish a connection to a URL and retrieve the data.

public Map> getHeaderFields() Returns an unmodifiable Map of the header fields. The Map keys are Strings that represent the response-header field names. Each Map value is an unmodifiable List of Strings that represents the corresponding field values.

This method considers only response headers set or added via

• setHeader(java.lang.String, java.lang.String)
• addHeader(java.lang.String, java.lang.String)
• setDateHeader(java.lang.String, long)
• addDateHeader(java.lang.String, long)
• setIntHeader(java.lang.String, int) or
• addIntHeader(java.lang.String, int) respectively.

Java Example:

The following code snippet shows how to create an URLConnection object and retrieve the HTTP response header:

package crunchify.com.tutorials; import java.net.URL; import java.net.URLConnection; import java.util.List; import java.util.Map; /** * @author Crunchify.com * Simple Way to Get HTTP Response Header in Java - conn.getHeaderFields() * */ public class CrunchifyHTTPResponseHeader < public static void main(String[] args) < try < URL crunchifyObject = new URL("https://crunchify.com"); URLConnection conn = crunchifyObject.openConnection(); Map> map = conn.getHeaderFields(); System.out.println("Printing All Response Header for URL: " + crunchifyObject.toString() + "\n"); for (Map.Entry> entry : map.entrySet()) < System.out.println(entry.getKey() + " : " + entry.getValue()); >System.out.println("\nGet Response Header By Key . \n"); List contentLength = map.get("Content-Length"); if (contentLength == null) < System.out.println("'Content-Length' doesn't present in Header!"); >else < for (String header : contentLength) < System.out.println("Content-Lenght: " + header); >> > catch (Exception e) < e.printStackTrace(); >> >

In this code snippet, we first create a URL object representing the URL we want to connect to. Finally, we retrieve the HTTP response header using the getHeaderFields() method, which returns a Map object containing the header fields and their corresponding values.

We can then iterate through the Map object using a for loop and print out each header field and its value. This will give us a clear idea of what information the HTTP response header contains.

It is important to note that the getHeaderFields() method returns a Map object where each key represents a header field and its value is a List of all the values for that field. This is because some header fields, such as the “Set-Cookie” field, can have multiple values.

In conclusion, retrieving the HTTP response header in Java is a simple task that can be accomplished using the built-in HttpURLConnection class. By using the getHeaderFields() method, we can easily retrieve the header fields and their values and use them in our application as needed.

Output:

Printing All Response Header for URL: https://crunchify.com Transfer-Encoding : [chunked] null : [HTTP/1.1 200 OK] Server : [cloudflare] CF-Ray : [79f5bf52ea6eaa70-DFW] X-Content-Type-Options : [nosniff] Connection : [keep-alive] X-Kinsta-Cache : [HIT] X-Edge-Location-Klb : [1] Date : [Sun, 26 Feb 2023 03:55:49 GMT] CF-Cache-Status : [DYNAMIC] Strict-Transport-Security : [max-age=63072000; includeSubDomains; preload] NEL : [] Report-To : [<"endpoints":[<"url":"https:\/\/a.nel.cloudflare.com\/report\/v3?s=QC8GDvDkbtoHpQUJfqPqowm0TACZvToi5DGIAraUXSoVebpKHgHkGIsFjgZF90vS7r%2BS%2Bkdk0XScg4sLhMr1weAbLgvRFY49CAzB7pCPdwwrZjFm%2BqUV3n5JQC3q6lk%3D">],"group":"cf-nel","max_age":604800>] Vary : [Accept-Encoding] Ki-CF-Cache-Status : [BYPASS] ki-cache-type : [None] alt-svc : [h3=":443"; ma=86400, h3-29=":443"; ma=86400] ki-edge : [v=17.19] Link : [; rel=shortlink] Content-Type : [text/html; charset=UTF-8] Get Response Header By Key . 'Content-Length' doesn't present in Header! Process finished with exit code 0

Let me know if you have any question about this program.

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