Reflections工具包

工作中配合Google Guice的使用，用到了Reflections工具包，记录一下，备忘。

项目地址： http://code.google.com/p/reflections/

从官方文档上，我们可以了解到它是一个用于Java运行时元数据分析，本着注解搜寻的精神。

用途：

Reflections scans your classpath, indexes the metadata, allows you to query it on runtime and may save and collect that information for many modules within your project.


Using Reflections you can query your metadata such as:

get all subtypes of some type
get all types/methods/fields annotated with some annotation, w/o annotation parameters matching
get all resources matching matching a regular expression

UseCases:

some useful use cases below:

bootstrap in a multi module environment
collect pre scanned metadata
serialize Reflections into a java source file, and use it to statically reference java elements
query the store directly, avoid definition of types in class loader
find resources in your classpath (for example all properties files)
optional parallel scanning
bootstrap in a multi module environment
In a multi module project, where each module is responsible for it's properties, jpa entities and maybe guice modules, use Reflections to collect that metadata and bootstrap the application

        Reflections reflections = new Reflections(new ConfigurationBuilder()
                .addUrls(ClasspathHelper.forPackage("your.package.here"),
                         ClasspathHelper.forClass(Entity.class), 
                         ClasspathHelper.forClass(Module.class))
                .setScanners(new ResourcesScanner(), 
                             new TypeAnnotationsScanner(), 
                             new SubTypesScanner()));

        Set<String> propertiesFiles = reflections.getResources(Pattern.compile(".*\\.properties"));
        Properties allProperties = createOneBigProperties(propertiesFiles);

        Set<Class<?>> jpaEntities = reflections.getTypesAnnotatedWith(Entity.class);
        SessionFactory sessionFactory = createOneBigSessionFactory(jpaEntities, allProperties);

        Set<Class<? extends Module>> guiceModules = reflections.getSubTypesOf(Module.class);
        Injector injector = createOneBigInjector(guiceModules);
collect pre scanned metadata
first configure your project's parent pom in the build.plugins section with Reflections, like this

            <plugin>
                <groupId>org.reflections</groupId>
                <artifactId>reflections-maven</artifactId>
                <version>0.9.8</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>reflections</goal>
                        </goals>
                        <phase>process-classes</phase>
                    </execution>
                </executions>
            </plugin>
than, on runtime, collect these pre saved metadata and instantiate Reflections

        Reflections reflections =
                isProduction() ? Reflections.collect() : new Reflections("your.package.here");
of course, saving the scanned metadata can be done without maven, by simply calling the save method

    public static void main(String[] args) {
        //from time to time, I run this main to regenerate saved metadata for Reflections
        new Reflections(new ConfigurationBuilder()
                .setUrls(ClasspathHelper.forPackage("my.project.prefix"))
                .setScanners(/*whatever*/))
                .save("src/main/resources/resource1-reflections.xml");

        new Reflections(new ConfigurationBuilder()
                .setUrls(ClasspathHelper.forPackage("my.project.prefix.model"))
                .filterInputsBy(new FilterBuilder().include(FilterBuilder.prefix("my.project.prefix.model")))
                .setScanners(new TypesScanner(), new TypeElementsScanner())
                .setSerializer(new JavaCodeSerializer()))
                .save("src/main/java/my.project.prefix.model.MyModelStore");
    }
serialize Reflections into a java source file, and use it to statically reference java elements
        Reflections reflections = new Reflections(new ConfigurationBuilder()
                .filterInputsBy(new FilterBuilder().include("model.package"))
                .setScanners(new TypesScanner(), new TypeElementsScanner())
                .setUrls(asList(ClasspathHelper.forPackage("model.package"))));

        String filename = System.getProperty("user.dir") + "/src/test/java/model.package.reflections.MyModelStore";
        reflections.save(filename, new JavaCodeSerializer());
replace "model.package" with your model's package prefix

this serializes types and types elements into interfaces respectively to fully qualified name, for example:

//generated using Reflections JavaCodeSerializer
public interface MyTestModelStore {
public interface org extends IPackage {
    public interface reflections extends IPackage {
                public interface TestModel$AC1 extends IClass {}
                public interface TestModel$C4 extends IClass {
                        public interface f1 extends IField {}
                        public interface m1 extends IMethod {}
...
}
than use the different resolve methods to resolve the serialized element into Class, Field or Method. for example:

Class<? extends IMethod> imethod = MyTestModelStore.org.reflections.TestModel$C4.m1.class;
Method method = JavaCodeSerializer.resolve(imethod);
can be useful to represent ognl statically and not in by strings or to use in annotations for marking fields or methods in a static manner

query the store directly, avoid definition of types in class loader
querying through Reflections results in classes defined by the class loader. this is usually not a problem, but in cases class definition is not desirable, you can query the store directly using strings only

        Reflections reflections = new Reflections(...); //see in other use cases
        Set<String> serializableFqns = reflections.getStore().getSubTypesOf("java.io.Serializable");
plus, you can create your specialized query methods by querying the store directly

        Map<String, Multimap<String, String>> storeMap = reflections.getStore().getStoreMap();
//or
        Multimap<String, String> scannerMap = reflections.getStore().get(ResourcesScanner.class);
find resources in your classpath
        Reflections reflections = new Reflections(new ConfigurationBuilder()
                .setUrls(ClasspathHelper.forPackage("your.package.here"))
                .setScanners(new ResourcesScanner());

        Set<String> propertiesFiles = reflections.getResources(Pattern.compile(".*\\.properties"));
        Set<String> hibernateCfgFiles = reflections.getResources(Pattern.compile(".*\\.cfg\\.xml"));
optional parallel scanning
        Reflections reflections = new Reflections(new ConfigurationBuilder()
                .filterInputsBy(...)
                .setScanners(...)
                .setUrls(...)
                .setExecutorService(Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors()));
will result in this log line when scanning:

[main] INFO  org.reflections.Reflections - Reflections took 164 ms to scan 1 urls, producing 13 keys and 23 values [using 2 cores]