在Android项目中使用Maven库

Question

I have a certain library project which does a certain work. The library is built using maven.

I now want to include this library in an android project. I added the library jar as a compile dependency in gradle and I can successfully use the library in my android code.

I have JDK 8 installed and I build the library using it. But, as I have read, android uses Java 7. Since the library is built using JDK 8, can this cause a problem?

If it can cause problems, I don't think building the library using JDK 7 would solve it either, since the library depends on other maven libraries from external maven repository. Is there anything I can do about it?

Answer 1

This is a common JDK lifecycle problem. The good news is there are things you can do to make sure that everything in your build is compliant with a certain JDK.

First off, make sure that your module is indeed compiled with the latest JDK version you are willing to accept. You can set the compiler plugin to only generate bytecode that is compliant to certain version, for instance JDK 7.

For example:

 <build>
    <plugins>
       <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.3</version>
        <configuration>
          <source>THE_JDK_VERSION_YOU_WANT</source>
          <target>THE_JDK_VERSION_YOU_WANT</target>
        </configuration>
      </plugin>
    </plugins>
  </build>

NOTE

There is a drawback to this and that is that while setting a specific source and target to the compiler, the code may still use JDK features that aren't available in the target environment's JRE. For example, having set JAVA_HOME to JDK8 and source and target to 1.7 will still allow the code to use (say) ConcurrentHashMap.mappingCount() which came in JDK8.

The answer to this problem is to use the animal-sniffer plugin. This plugin will check your code for any usage of disallowed API:s, such as JDK8, if you configure it that way. This plugin was previously hosted by Codehaus, but it will come up if Google around a bit. I can provide you with a working example tomorrow when I get back to work.

Next, as you pointed out, you have your dependencies. Fortunately, the enforcer plugin can use an extended rule-set, called <enforceBytecodeVersion> that can check that all of your dependencies are also compliant with a specific bytecode version. All the details are available here .

EDITED

Here comes the configuration for the animal-sniffer plugin. There's a newer version available (1.14), but it didn't work for me. Maybe you'll have better luck. The API signatures for the JDK are available at Maven Central.

<plugin>
  <groupId>org.codehaus.mojo</groupId>
  <artifactId>animal-sniffer-maven-plugin</artifactId>
  <version>1.13</version>
  <executions>
    <execution>
      <id>check-for-jdk6-compliance</id>
      <phase>test</phase>
      <goals>
        <goal>check</goal>
      </goals>
    </execution>                
  </executions>
  <configuration>
    <signature>
      <groupId>org.codehaus.mojo.signature</groupId>
      <artifactId>java16</artifactId>
      <version>1.1</version>
    </signature>
  </configuration>
</plugin>