如何使用ANT构建具有不同Java版本的jar

Question

I tried to build a jar file using java 1.5. I use eclise and I specified the java version as 1.5 in below areas.

• Project -> Properties -> Java Compiler
• Project -> Java Build Path -> JRE System Library
• Ant Build File -> Run As -> ExternalToolConfiguration -> JRE

But after the jar is built all the classes were built in 1.7 (major version 51) I want them in 1.5.(49) This is the result for javap -verbose MyClassInBuiltJar

SourceFile: "Program.java"
minor version: 0
major version: 51
Constant pool:

Answer 1

It's probably not ANT that cause the issue, you may need to change the project's JRE and recompile the project with the 1.5 JRE .

You can also try to specify the JRE used directly in your build.xml file.

Answer 2

You can use source=1.5 and target=1.5 in javac ant task. See here for details javac

Answer 3

You need to explicitly specify the source and target in the build.xml:

<property name="javac.source"  value="1.5"/>
<property name="javac.target"  value="1.5"/>
<javac source="${javac.source}"  target="${javac.target}">