Ant properties controlling javac

The source and target attributes of <javac>don't have any default values for historical reasons. Since theunderlying javac compiler's default depends on the JDK you use, youmay encounter build files that don't explicitly set those attributesand that will no longer compile using a newer JDK. If you cannotchange the build file, Apache Ant provides two properties that help yousetting default values for these attributes. If the attributes havebeen set explicitly, the properties listed here will be ignored.

ant.build.javac.source

Since Ant 1.7

Provides a default value for <javac>'s and<javadoc>'s source attribute.

ant.build.javac.target

Since Ant 1.7

Provides a default value for <javac>'s targetattribute.