JavaDay talk about code generation with javac plugin

1. CODE GENERATION
WITH JAVAC PLUGIN

2. Hello!
I am Oleksandr Radchykov
committed.chinchilla@gmail.com
belict

3. Agenda
1. Motivation
2. How to generate code?
3. How to create plugin
4. Demo

4. Motivation for
code generation

5. Getting rid of boilerplate
class MyService {
private final String name;
private final Integer version;
public MyService(String name, Integer version) {
this.name = name;
This.version = version;
}
public String getName() { return name; }
public Integer getVersion() { return version; }
}

6. @Getter
@RequiredArgsConstructor
class MyService {
private final String name;
private final Integer version;
}
6

7. Getting rid from annoying
code duplication
public String validate(Object input) {
if (income instanceof String
&& !((String) income).isEmpty()) {
return (String) income;
}
…
}

8. public String validate(Object input) {
if (income instanceof String && !income.isEmpty()) {
return income;
}
…
}
8

9. Two ways to
generate code

10. Annotation Processing
▷Java 5+
▷Takes java code and generates source files
▷You can not manipulate an existing java code
▷Use the model of processing rounds

11. Javac Plugin
▷Since Java 8
▷Can give us access to AST trees parsed from
source code
▷Can be used to add compile-time checks
▷Can run on different phases of compilation
process

12. How to create
javac plugin?

13. 1. Implement Plugin interface
import com.sun.source.util.Plugin;
class MyPlugin implements Plugin {
@Override
public String getName() { return “pluginName”; }
@Override
public void init(JavacTask javacTask,
String… strings) {
/*...*/
}
}

14. 2. Create provider-configuration file
MyPlugin.jar
- com/example
- MyPlugin.class
- META-INF/services
- com.sun.source.util.Plugin
Provider-configuration file should declare all plugins
you want to expose.

15. 3. Compilation
$ javac -Xplugin:PluginName
–cp /path/to/plugin
Source.java

16. Demo

17. Questions?

18. Thanks
committed.chinchilla@gmail.com
belict