Building a RestTemplate using RestTemplateBuilder fails with a ClassNotFoundException when OkHttp 2 is on the classpath

[jmirc]

I just updated a project with Spring Boot 2.0.2 and I am getting the following exception

Caused by: java.lang.IllegalArgumentException: Could not find class [org.springframework.http.client.OkHttpClientHttpRequestFactory]
	at org.springframework.util.ClassUtils.resolveClassName(ClassUtils.java:313)
	at org.springframework.boot.web.client.RestTemplateBuilder.detectRequestFactory(RestTemplateBuilder.java:600)
	at org.springframework.boot.web.client.RestTemplateBuilder.configureRequestFactory(RestTemplateBuilder.java:566)
	at org.springframework.boot.web.client.RestTemplateBuilder.configure(RestTemplateBuilder.java:535)
	at org.springframework.boot.web.client.RestTemplateBuilder.build(RestTemplateBuilder.java:523)
	at org.springframework.boot.web.client.RestTemplateBuilder.build(RestTemplateBuilder.java:509)
	at org.springframework.boot.test.web.client.TestRestTemplate.<init>(TestRestTemplate.java:133)

The RestTemplateBuilder is trying to validate if some HTTP client factories exist and the org.springframework.http.client.OkHttpClientHttpRequestFactory doesn't exist anymore in Spring Framework.

[wilkinsona]

Thanks for the report. Which version of Spring Boot were you using before you upgraded?

[jmirc]

I used the version 2.0.1

[wilkinsona]

Thanks. That's rather surprising as support for OkHttp 2 was dropped from Spring Framework in 5.0.0.RC1. We've missed aligning RestTemplateBuilder with that, but I would not expect an upgrade from Spring Boot 2.0.1 to 2.0.2 to trigger the problem. Rather, any Spring Boot 2.0.x version should be affected. Perhaps you could clarify the situation by providing a small sample that works with 2.0.1 and fails with 2.0.2?

[chrismathews]

I just hit this same issue myself. I have a project that is using Spring Boot 2.0.1.RELEASE in my case. The project is very simple but pulls in an internal dependency that transitively depends on OkHttp2.

As best as I can tell the problem is in: https://github.com/spring-projects/spring-boot/blob/v2.0.1.RELEASE/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/client/RestTemplateBuilder.java

In particular:

static {
		Map<String, String> candidates = new LinkedHashMap<>();
		candidates.put("org.apache.http.client.HttpClient",
				"org.springframework.http.client.HttpComponentsClientHttpRequestFactory");
		candidates.put("okhttp3.OkHttpClient",
				"org.springframework.http.client.OkHttp3ClientHttpRequestFactory");
		candidates.put("com.squareup.okhttp.OkHttpClient",
				"org.springframework.http.client.OkHttpClientHttpRequestFactory");
		REQUEST_FACTORY_CANDIDATES = Collections.unmodifiableMap(candidates);
	}

Since Spring Framework 5 doesn't support OkHttp2 it would seem to me that com.squareup.okhttp.OkHttpClient should not be an option in the candidates list. Since it is there when this code gets invoked:

private ClientHttpRequestFactory detectRequestFactory() {
		for (Map.Entry<String, String> candidate : REQUEST_FACTORY_CANDIDATES
				.entrySet()) {
			ClassLoader classLoader = getClass().getClassLoader();
			if (ClassUtils.isPresent(candidate.getKey(), classLoader)) {
				Class<?> factoryClass = ClassUtils.resolveClassName(candidate.getValue(),
						classLoader);
				return (ClientHttpRequestFactory) BeanUtils
						.instantiateClass(factoryClass);
			}
		}
		return new SimpleClientHttpRequestFactory();
	}

While debugging I can see ClassUtils.isPresent() returns true for com.squareup.okhttp.OkHttpClient and then ClassUtils.resolveClassName() promptly throws an exception for org.springframework.http.client.OkHttpClientHttpRequestFactory.

The resulting stacktrace looks like:

java.lang.IllegalStateException: Failed to load ApplicationContext

	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:125)
	at org.springframework.test.context.support.DefaultTestContext.getApplicationContext(DefaultTestContext.java:108)
	at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:117)
	at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:83)
	at org.springframework.boot.test.autoconfigure.SpringBootDependencyInjectionTestExecutionListener.prepareTestInstance(SpringBootDependencyInjectionTestExecutionListener.java:44)
	at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:246)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:227)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:289)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:291)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:246)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.test.web.client.TestRestTemplate': Initialization of bean failed; nested exception is java.lang.IllegalArgumentException: Could not find class [org.springframework.http.client.OkHttpClientHttpRequestFactory]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:587)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:741)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:327)
	at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:138)
	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:99)
	at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:117)
	... 30 more
Caused by: java.lang.IllegalArgumentException: Could not find class [org.springframework.http.client.OkHttpClientHttpRequestFactory]
	at org.springframework.util.ClassUtils.resolveClassName(ClassUtils.java:311)
	at org.springframework.boot.web.client.RestTemplateBuilder.detectRequestFactory(RestTemplateBuilder.java:600)
	at org.springframework.boot.web.client.RestTemplateBuilder.configureRequestFactory(RestTemplateBuilder.java:566)
	at org.springframework.boot.web.client.RestTemplateBuilder.configure(RestTemplateBuilder.java:535)
	at org.springframework.boot.web.client.RestTemplateBuilder.build(RestTemplateBuilder.java:523)
	at org.springframework.boot.web.client.RestTemplateBuilder.build(RestTemplateBuilder.java:509)
	at org.springframework.boot.test.web.client.TestRestTemplate.<init>(TestRestTemplate.java:133)
	at org.springframework.boot.test.web.client.TestRestTemplateContextCustomizer$TestRestTemplateFactory.setApplicationContext(TestRestTemplateContextCustomizer.java:146)
	at org.springframework.context.support.ApplicationContextAwareProcessor.invokeAwareInterfaces(ApplicationContextAwareProcessor.java:120)
	at org.springframework.context.support.ApplicationContextAwareProcessor.postProcessBeforeInitialization(ApplicationContextAwareProcessor.java:96)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:422)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1694)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:579)
	... 45 more
Caused by: java.lang.ClassNotFoundException: org.springframework.http.client.OkHttpClientHttpRequestFactory
	at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	at org.springframework.util.ClassUtils.forName(ClassUtils.java:274)
	at org.springframework.util.ClassUtils.resolveClassName(ClassUtils.java:308)
	... 57 more

[wilkinsona]

Thanks, @chrismathews. Your analysis matches my own which is why I was surprised that @jmirc had only seen the problem when upgrading from 2.0.1 to 2.0.2.

[chrismathews]

Thanks for the quick turnaround Andy!

[jmirc]

Hi Andy, sorry for my late reply. I checked why with the Spring Boot 2.0.1.RELEASE I didn't get the issue.

I didn't get the issue with the previous version because of the RestTemplateBuilder class that used the apache http client library provided by spring-cloud-commons.
With the Spring Boot 2.0.2.RELEASE, the apache http client library is not provided any more and the RestTemplateBuilder class used the okhttp client that I have on the classpath.