Maven-shade plugin - how to resolve version mismatch

Question

My project used to have a dependency on spring-boot 2.7.18. I'm now in the process of bumping that to 3.3.5. My project also depends on Foo, which depends on spring-boot 2.7.18. As you can tell, there's a conflict in spring-boot versions (3.3.5 vs 2.7.18).

Also, my project used to depend on httpclient 4. Now that I'm bumping my spring-boot version, Spring gets bumped from 5 to 6. Spring 6 requires httpclient 5. Therefore, I'm also bumping my httpclient version from 4 to 5. However, Foo depends on httpclient 4. Yet again, there's a conflict in httpclient versions (4.x vs 5.x)

I'm trying to address both of those dependency version mismatches using the maven-shade plugin. I want Foo to keep using spring-boot 2.7.18 and httpclient 4 while my project uses spring-boot 3.3.5 and httpclient 5.

Somewhere in Foo, there's the following code

import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
...
CloseableHttpClient httpClient = HttpClients.custom().setSSLSocketFactory(sslSocketFactory).build();
restTemplateBuilder = restTemplateBuilder.requestFactory(() -> new HttpComponentsClientHttpRequestFactory(httpClient));

I see the following compile-time error in IntelliJ:

Required type: HttpClient

Provided type: CloseableHttpClient

That's because the signature of the HttpComponentsClientHttpRequestFactory constructor has changed from accepting a CloseableHttpClient instance to accepting an HttpClient instance.

As I said, I'm trying to use the maven-shade plugin to resolve the dependency version mismatch. Here's the relevant section of pom.xml

<plugin>
  <artifactId>maven-shade-plugin</artifactId>
  <version>3.6.0</version>
  <executions>
    <execution>
      <phase>package</phase>
      <goals>
        <goal>shade</goal>
      </goals>
      <configuration>
        <artifactSet>
          <includes>
            <include>Foo</include>
          </includes>
        </artifactSet>
        <relocations>
          <relocation>
            <pattern>org.springframework.http.client</pattern>
              <shadedPattern>shaded.org.springframework.http.client</shadedPattern>
          </relocation>
          <relocation>
            <pattern>org.apache.http</pattern>
            <shadedPattern>shaded.org.apache.http</shadedPattern>
          </relocation>
        </relocations>
        <promoteTransitiveDependencies>true</promoteTransitiveDependencies>
        <createDependencyReducedPom>true</createDependencyReducedPom>
      </configuration>
    </execution>
  </executions>
</plugin>

Unfortunately, I'm still seeing the same error. This is my first time using the maven-shade plugin. Can you please help me figure out how I need to configure the pom.xml to resolve the issue?

Fyi I'm using Java 21.

Answer 1

It turns out that the httpclient version mismatch wasn't the actual problem. Since httpclient 4 and httpclient 5 are in different namespaces, no shading was required there.

The actual problem was the spring version mismatch caused by the spring-boot version bump. That's what I needed to address.

At first, I tried to shade org.springframework in the root project's pom.xml (let's call the root project Qux). However, I eventually realized that it wasn't possible to do so because I can't have both spring-boot 2 and spring-boot 3 on the same classpath. Therefore, either Qux would fail because spring-boot 2 was on the classpath or Foo would fail because spring-boot 3 was on the classpath, and all my shading was in vain.

Finally, I realized that I have to perform the shading in Foo's pom.xml. Since I didn't have direct access to Foo's source code, I created 2 new modules via IntelliJ: a parent one and Bar. Bar has a dependency on Foo. I shaded org.springframework in Bar's xml. In the parent pom.xml, I added Bar and Qux to the section. Now, everything works like a charm.