Using RestTemplate on DesktopApplication (Non-WebBased)

Question

I am working on a Desktop Application, with OpenJfx and SpringBoot. It works well thus far.

However, this application will consume a WebService and I want to use RestTemplate. When I add spring-web dependency to my pom.xml file, Spring Boot attempts to instantiate several things for which I do not have use.

The dependency added:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>5.0.7.RELEASE</version>
</dependency>

First, the following error is displayed:

[2020-08-11 10:26:20] - WARN  - Exception encountered during context initialization - cancelling refresh attempt: org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.context.ApplicationContextException: Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean. [AbstractApplicationContext.java:558] 

I added the following propery, as per this response:

spring.main.web-application-type=none

Running the application again, more things attempt to instantiate:

[2020-08-11 10:29:47] - WARN  - Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'jacksonObjectMapper' defined in class path resource [org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration$JacksonObjectMapperConfiguration.class]: Unsatisfied dependency expressed through method 'jacksonObjectMapper' parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jacksonObjectMapperBuilder' defined in class path resource [org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration$JacksonObjectMapperBuilderConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.http.converter.json.Jackson2ObjectMapperBuilder]: Factory method 'jacksonObjectMapperBuilder' threw exception; nested exception is java.lang.NoSuchMethodError: org.springframework.http.converter.json.Jackson2ObjectMapperBuilder.visibility(Lcom/fasterxml/jackson/annotation/PropertyAccessor;Lcom/fasterxml/jackson/annotation/JsonAutoDetect$Visibility;)Lorg/springframework/http/converter/json/Jackson2ObjectMapperBuilder; [AbstractApplicationContext.java:558] 
[2020-08-11 10:29:47] - INFO  - 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled. [ConditionEvaluationReportLoggingListener.java:136] 
[2020-08-11 10:29:47] - ERROR - 

***************************
APPLICATION FAILED TO START
***************************

Description:

An attempt was made to call a method that does not exist. The attempt was made from the following location:

    org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$Jackson2ObjectMapperBuilderCustomizerConfiguration$StandardJackson2ObjectMapperBuilderCustomizer.configureVisibility(JacksonAutoConfiguration.java:258)

The following method did not exist:

    org.springframework.http.converter.json.Jackson2ObjectMapperBuilder.visibility(Lcom/fasterxml/jackson/annotation/PropertyAccessor;Lcom/fasterxml/jackson/annotation/JsonAutoDetect$Visibility;)Lorg/springframework/http/converter/json/Jackson2ObjectMapperBuilder;

The method's class, org.springframework.http.converter.json.Jackson2ObjectMapperBuilder, is available from the following locations:

    jar:file:/C:/Users/xxx/.m2/repository/org/springframework/spring-web/5.0.7.RELEASE/spring-web-5.0.7.RELEASE.jar!/org/springframework/http/converter/json/Jackson2ObjectMapperBuilder.class

It was loaded from the following location:

    file:/C:/Users/xxx/.m2/repository/org/springframework/spring-web/5.0.7.RELEASE/spring-web-5.0.7.RELEASE.jar


Action:

Correct the classpath of your application so that it contains a single, compatible version of org.springframework.http.converter.json.Jackson2ObjectMapperBuilder
 [LoggingFailureAnalysisReporter.java:40] 

The problem is, I only want to use RestTemplate to consume a Rest Service. Is there a way I can add Classes native to other spring libraries, without all the additional baggage?

Answer 1

RestTemplate is only a wrapper around a HttpClient implementation. That http client needs to be provided by someone for example an underlying server implementation like tomcat, undertow, netty, jetty etc. But can also come from a standalone client.

So if we walk through your errors:

[2020-08-11 10:26:20] - WARN  - Exception encountered during context initialization - cancelling refresh attempt: org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.context.ApplicationContextException: Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean. [AbstractApplicationContext.java:558] 

This says that it can't start a server, because you have pulled in spring-web which is a lot of classes that needs a server. It tries to autostart a lot of classes.

spring.main.web-application-type=none

So with this parameter you basically disable all the autostart classes that will get run if you have a web application. This will not disable the creation of the spring context (the context is needed to create all spring classes, to make sure autowiring works, beans etc etc)

[2020-08-11 10:29:47] - WARN  - Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'jacksonObjectMapper' defined in class path resource [org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration$JacksonObjectMapperConfiguration.class]: Unsatisfied dependency expressed through method 'jacksonObjectMapper' parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jacksonObjectMapperBuilder' defined in class path resource [org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration$JacksonObjectMapperBuilderConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.http.converter.json.Jackson2ObjectMapperBuilder]: Factory method 'jacksonObjectMapperBuilder' threw exception; nested exception is java.lang.NoSuchMethodError: org.springframework.http.converter.json.Jackson2ObjectMapperBuilder.visibility(Lcom/fasterxml/jackson/annotation/PropertyAccessor;Lcom/fasterxml/jackson/annotation/JsonAutoDetect$Visibility;)Lorg/springframework/http/converter/json/Jackson2ObjectMapperBuilder; [AbstractApplicationContext.java:558] 

So when you run it now it tries to create the context and fails because it can't find Jackson because jackson is needed and is created using the autostart classes that you disabled with your previous parameter.

Its basically saying you want to use a car, but you don't want the engine, wheels, interior, doors, steering wheel etc. etc. If you don't have a server or anything for that matter that provides the HttpClient there is nothing for RestTemplate to use or wrap around.

If you are looking for a standalone simple rest client i would suggest looking into OkHttp