备忘：maven 中指定版本

     <build>
        <plugins>
          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
              <source>1.7</source>
              <target>1.7</target>
            </configuration>
          </plugin>
        </plugins>
    </build>
<!--     <profiles>
    <profile>
      <id>env-dev</id>

      <activation>
        <activeByDefault>true</activeByDefault>
        <jdk>1.7</jdk>
        <property>
          <name>target-env</name>
          <value>dev</value>
        </property>
      </activation>

      <properties>
          <maven.compiler.source>1.6</maven.compiler.source>
          <maven.compiler.target>1.6</maven.compiler.target>
          <maven.compiler.compilerVersion>1.6</maven.compiler.compilerVersion>
      </properties>
    </profile>
    </profiles> -->