How to Send an HTTP Header With Every Request With Spring RestTemplate

In Know Which Apps Are Hitting Your Web Service, I showed how to write a servlet filter that enforces the existence of a special HTTP request header.

From a client perspective, it would be nice to send this header automatically, instead of having to set the header manually with every request. This post shows how we can use Spring’s RestTemplate and ClientHttpRequestInterceptor to accomplish this.

First we need to implement a ClientHttpRequestInterceptor:

package com.myapp.connector;

import java.io.IOException;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpRequest;
import org.springframework.http.client.ClientHttpRequestExecution;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.http.client.ClientHttpResponse;

public class XUserAgentInterceptor implements ClientHttpRequestInterceptor {

    @Override
    public ClientHttpResponse intercept(
            HttpRequest request, byte[] body, ClientHttpRequestExecution execution)
            throws IOException {

        HttpHeaders headers = request.getHeaders();
        headers.add("X-User-Agent", "My App v2.1");
        return execution.execute(request, body);
    }
}

Now we need to configure our RestTemplate to use it. Here I’m using Spring’s Java-based configuration, but you can implement the same thing with the XML-based configuration too:

package com.myapp;

import java.util.Collections;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.web.client.RestTemplate;
import com.myapp.connector.XUserAgentInterceptor;

@Configuration
public class MyAppConfig {

    @Bean
    public RestTemplate restTemplate() {
        RestTemplate restTemplate = new RestTemplate(clientHttpRequestFactory());
        restTemplate.setInterceptors(Collections.singletonList(new XUserAgentInterceptor()));
        return restTemplate;
    }
}

With this configuration, any requests you make through the RestTemplate will automatically carry the desired HTTP request header.

To learn how to set request timeouts automatically, see my post How to Set HTTP Request Timeouts With Spring RestTemplate.

http://springinpractice.com/2013/10/27/how-to-send-an-http-header-with-every-request-with-spring-resttemplate/

When creating a web service, it’s often useful to know which apps are hitting it. I don’t mean which users, but instead which apps. The reason is that you may want to coordinate with some other team on something. For example, maybe the team is being too aggressive about request retries, or maybe you want to alert the team to a change in the API. Whatever the reason, it’s good to know which apps are calling your service.

HTTP has a User-Agent header that can help here. One possible approach is to make that a required header. Unfortunately, this approach isn’t ideal. The problem is that HTTP client libraries usually set that header automatically. So if the client application forgets to set the header explicitly, you end up with user agents like Apache-HttpClient/release (java 1.5), which isn’t much help at all.

An approach I like better is to define a custom header and make it required. I use X-User-Agent, since it really is a user agent we’re talking about here.

Here’s how to implement this with a servlet filter. No Spring involved here at all; it’s just servlet stuff.

package com.myapp.web.filter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class XUserAgentFilter implements Filter {
    private static final String X_USER_AGENT = "X-User-Agent";

    private String errorJson;

    public XUserAgentFilter() {
        String message = 
            "HTTP header '" + X_USER_AGENT + "' is required. Please set it to your application name so we know " +
            "who to contact if there's an issue.";
        this.errorJson = "{ " + wrap("message") + " : " + wrap(message) + " }";
    }

    private String wrap(String s) { return "\"" + s + "\""; }

    @Override
    public void init(FilterConfig config) throws ServletException { }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;

        if (httpRequest.getHeader(X_USER_AGENT) == null) {//不走chain.doFilter即结束
            httpResponse.setStatus(422);
            httpResponse.getWriter().println(errorJson);
        } else {
            chain.doFilter(request, response);
        }
    }

    @Override
    public void destroy() { }
}

Of course, you need to configure this filter and a filter mapping in your web.xml file.

In the next post I’ll show you how to set up your Spring RestTemplate to send the X-User-Agent header with each request automatically.

http://springinpractice.com/2013/10/25/know-which-apps-are-hitting-your-web-service/

package com.myapp;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

@Configuration
public class MyAppConfig {

    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate(clientHttpRequestFactory());
    }

    private ClientHttpRequestFactory clientHttpRequestFactory() {
        HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory();
        factory.setReadTimeout(2000);
        factory.setConnectTimeout(2000);
        return factory;
    }
}

<bean class="org.springframework.web.client.RestTemplate">
    <constructor-arg>
        <bean class="org.springframework.http.client.HttpComponentsClientHttpRequestFactory"
            p:readTimeout="2000"
            p:connectTimeout="2000" />
    </constructor-arg>
</bean>

http://springinpractice.com/2013/10/27/how-to-set-http-request-timeouts-with-spring-resttemplate/

Basic Auth：

// Set the username and password for creating a Basic Auth request
HttpAuthentication authHeader = new HttpBasicAuthentication(username, password);
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setAuthorization(authHeader);
HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the String message converter
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

try {
    // Make the HTTP GET request to the Basic Auth protected URL
    ResponseEntity<Message> response = restTemplate.exchange(url, HttpMethod.GET, requestEntity, String.class);
    return response.getBody();
} catch (HttpClientErrorException e) {
    Log.e(TAG, e.getLocalizedMessage(), e);
    // Handle 401 Unauthorized response
}

http://docs.spring.io/autorepo/docs/spring-android/1.0.x/reference/html/rest-template.html