Provide multiple connection pools

[bmeurant]

Today resthub comes with a unique bonecp connection pool, configured with default values.

HikariCP seems to be a good and very powerful alternative and could be proposed to replace BoneCP but it requires Java7 and we do not want to force resthub users to move to Java7.

This PR provides:

• some extension points to change connection pool
• a default activated (via spring profile) bonecp configuration
• an optional (to activate instead of bonecp) hikaricp configuration
• new configuration allowing to customize any bonecp option (and not only resthub defaults)

Main changes

• spring "resthub-pool-bonecp" should now be activated in order to use default provided bonecp configuration
• spring "resthub-pool-hikaricp" could replace the previous one in order to change connection pool
• to use hikariCP, users must add hikaricp maven dependency (optional in resthub) and exclude bonecp :

         <dependency>
            <groupId>org.resthub</groupId>
            <artifactId>resthub-jpa</artifactId>
            <version>${resthub.spring.stack.version}</version>
            <exclusions>
                <exclusion>
                    <groupId>com.jolbox</groupId>
            <artifactId>bonecp-spring</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

        <dependency>
            <groupId>com.zaxxer</groupId>
            <artifactId>HikariCP</artifactId>
            <version>1.2.9</version>
            <optional>true</optional>
        </dependency>

• unique database.properties configuration file has been splitted into two files datasource.properties and persistence.properties in order to allow full connection pool options override. Default datasource.properties is empty due to resthub defaults (can be ommited).

fixes #222, fixes #242

[bclozel]

BTW, I've been told HikariCP does not require JDK7 anymore, even though maximum performance should be expected with JDK7, according to their FAQ. Also, see this Spring Boot issue.

[brettwooldridge]

@bclozel Yes, as of HikariCP 1.3.2 (the current release) we no longer require Java7 (Java6 is now supported). Performance differences are due to improvements in the JVM and nothing inherent to the HikariCP pool itself, and I would expect HikariCP to outperform other pools by a similar margin on Java6. While performance is nice, reliability is most important and is/was always the primary goal of the HikariCP project. In our deployments, we experienced too many stability issues with other pools in production and got sick of it. HikariCP has never had a reported deadlock or livelock.

You may wish to update the HikariCP dependency to 1.3.2.