answered 2017-04-10 23:53:55 -0700

sosul
1 ●1 ●2 ●4

This was due to missing run-time dependency. After adding maven-bundle-plugin configurations in {project}-impl/pom.xml file, I could establish HttpClient connection.

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.felix</groupId>
      <artifactId>maven-bundle-plugin</artifactId>
      <extensions>true</extensions>
      <configuration>
        <instructions>
          <Export-Package>
            org.apache.*,
            org.springframework.*
          </Export-Package>
          <Import-Package>
            *;resolution:=optional
          </Import-Package>
          <Embed-Dependency>
            httpclient;type=!pom;inline=false,
            httpcore;type=!pom;inline=false,
            spring-web;type=!pom;inline=false
          </Embed-Dependency>
          <Embed-Transitive>true</Embed-Transitive>
          <Include-Resource>{maven-resources}</Include-Resource>
        </instructions>
      </configuration>
    </plugin>
  </plugins>
</build>