diamond operator is not supported in -source 1.5

 代码中 会让补全，否则会报 diamond operator is not supported in -source 1.5 

需要在POM中指定 source 版本号

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <source>1.7</source>
        <target>1.7</target>
        <encoding>UTF-8</encoding>
    </configuration>
</plugin>