Spring Boot - Caused by: java.lang.UnsupportedClassVersionError: org/glassfish/jersey/server/ResourceConfig : unsupported classversion 51.0 - spring

Question

I'm using Spring Boot and spring-boot-starter-jersey, for my application.
Initially I was working on Java 1.7 and everything worked fine.
But when I moved to Java 1.6 it started giving me error.
Caused by: java.lang.UnsupportedClassVersionError:
org/glassfish/jersey/server/ResourceConfig : unsupported classversion 51.0
I don't want to use java 1.7. How can i get rid of this error in java 1.6.
Also, on Spring boot site I couldn't find suitable version of spring-boot-starter-jersey for java 1.6
Below is my POM
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.2.0.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jersey</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
<version>1.2.0.RELEASE</version>
</dependency>
</dependencies>
<properties>
<tomcat.version>7.0.59</tomcat.version>
</properties>

Answer 1

Jersey 2.7 and up is compiled with Java 7. So if you want to use Java 6, you need to use Jersey 2.6. So you will need to get rid of the Jersey starter
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jersey</artifactId>
</dependency>
All the starter does is pull in a bunch of dependencies, it doesn't do anything code-wise. So all you really need to do is replace the dependencies with different versions in your pom. If you look at the actual pom for spring-boot-starter-jersey, you can see everything it pulls in. Below is a revised version of what you should add in place of spring-boot-starter-jersey
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-validator</artifactId>
</dependency>
<dependency>
<groupId>org.glassfish.jersey.containers</groupId>
<artifactId>jersey-container-servlet</artifactId>
<version>${jersey.version}</version>
</dependency>
<dependency>
<groupId>org.glassfish.jersey.ext</groupId>
<artifactId>jersey-spring3</artifactId>
<version>${jersey.version}</version>
<exclusions>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
</exclusion>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
</exclusion>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
</exclusion>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.jaxrs</groupId>
<artifactId>jackson-jaxrs-json-provider</artifactId>
<version>2.4.4</version>
</dependency>
{jersey.version} is 2.6.
A couple differences is that I am excluding everything Spring from the jersey-spring3. I'm doing this because you are already pulling everything in with the spring-boot-starter-web.
Also the jersey-media-json-jackson used in the Jersey start pom, we can't use that, unless you want to be stuck with using Jackson 1.9. So instead we just pull in underlying Jackson provider jackson-jaxrs-json-provider. The version we are using is the same Jackson version in Spring Boot bom.
The only other thing you need to do is configure the Jackson support for Jersey, that just includes registering the providers. You can just use the following feature.
import com.fasterxml.jackson.jaxrs.base.JsonMappingExceptionMapper;
import com.fasterxml.jackson.jaxrs.base.JsonParseExceptionMapper;
import com.fasterxml.jackson.jaxrs.json.JacksonJaxbJsonProvider;
import javax.ws.rs.core.Feature;
import javax.ws.rs.core.FeatureContext;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.MessageBodyWriter;
public class JacksonFeature implements Feature {
#Override
public boolean configure(FeatureContext context) {
context.register(JsonParseExceptionMapper.class);
context.register(JsonMappingExceptionMapper.class);
context.register(JacksonJaxbJsonProvider.class,
MessageBodyReader.class, MessageBodyWriter.class);
return true;
}
}
Just register it with your ResourceConfig... register(JacksonFeature.class).
That's really it, Everything should still work the same. The auto configuration should still be in tact. I tested it, not rigorously, but works for a simple startup.
UPDATE
Or as #Andy Wilkinson suggesed, you can keep the spring-boot-starter-jersey, and just set the property <jersey.version>2.6</jersey.version> in your pom. But if you want to use Jackson 2, just exclude jersey-media-json-jackson (as Jersey 2.6 pulls uses Jackson 1.9.3), and just include the jackson-jaxrs-json-provider as mentioned above, and follow the rest of the instructions to configure it.