annotation processor and compiler plugin
TRANSCRIPT
Annotation processor and compiler plugin as code generators.
Agenda
1.Motivation2.How to generate code?3.How to annotation processor4.How to create plugin5.Demo
Motivation for code generation
Getting rid of boilerplateclass 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; }}
@Getter@RequiredArgsConstructorclass MyService { private final String name; private final Integer version;}
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Getting rid from annoying code duplicationpublic String validate(Object input) { if (income instanceof String
&& !((String) income).isEmpty()) { return (String) income; } …}
public String validate(Object input) { if (income instanceof String && !income.isEmpty()) { return income; } …}
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Two ways to generate code
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
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
Annotation processor
1. Implement AbstractProcessor interface
import javax.annotation.processing.AbstractProcessor;
class MyProcessor implements AbstractProcessor {
@Override public boolean process(
Set<? Extends TypeElement> annotations, RoundEnvironment roundEnv) {
/*...*/ }
}
2. Create provider-configuration file
MyProcessor.jar- com/example
- MyProcessor.class- META-INF/services
- javax.annotation.processing.Processor
Provider-configuration file should declare all annotation processors you want to expose.
3. Compilation
$ javac –cp processor.jar \ *sources*.java
Javac plugin
1. Implement Plugin interfaceimport com.sun.source.util.Plugin;
class MyPlugin implements Plugin { @Override public String getName() { return “pluginName”; }
@Override public void init(JavacTask javacTask,
String… strings) { /*...*/ }}
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.
3. Compilation
$ javac -Xplugin:PluginName \ –cp /path/to/plugin \
Source.java
Demo
Questions?
