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package com.todoroo.andlib.service;
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import java.lang.reflect.Field;
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import java.util.Arrays;
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/**
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* Simple Dependency Injection Service for Android.
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* <p>
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* Add dependency injectors to the injector chain, then invoke this method
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* against classes you wish to perform dependency injection for.
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* <p>
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* All errors encountered are handled as warnings, so if dependency injection
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* seems to be failing, check the logs for more information.
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*
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* @author Tim Su <tim@todoroo.com>
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*
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*/
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public class DependencyInjectionService {
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private static final String QUALIFIED_PACKAGE = "com.t"; //$NON-NLS-1$
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/**
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* Dependency injectors. Use getters and setters to modify this list
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*/
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private AbstractDependencyInjector[] injectors = {};
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/**
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* Perform dependency injection in the caller object
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*
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* @param caller
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* object to perform DI on
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*/
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@SuppressWarnings("nls")
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public void inject(Object caller) {
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// Traverse through class and all parent classes, looking for
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// fields declared with the @Autowired annotation and using
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// dependency injection to set them as appropriate
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Class<?> cls = caller.getClass();
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while(cls != null) {
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String packageName = cls.getPackage().getName();
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if(!packageName.startsWith(QUALIFIED_PACKAGE))
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break;
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for(Field field : cls.getDeclaredFields()) {
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if(field.getAnnotation(Autowired.class) != null) {
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field.setAccessible(true);
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try {
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handleField(caller, field);
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} catch (IllegalStateException e) {
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throw new RuntimeException(String.format("Unable to set field '%s' of type '%s'",
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field.getName(), field.getType()), e);
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} catch (IllegalArgumentException e) {
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throw new RuntimeException(String.format("Unable to set field '%s' of type '%s'",
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field.getName(), field.getType()), e);
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} catch (IllegalAccessException e) {
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throw new RuntimeException(String.format("Unable to set field '%s' of type '%s'",
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field.getName(), field.getType()), e);
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}
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}
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}
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cls = cls.getSuperclass();
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}
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}
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/**
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* This method returns the appropriate dependency object based on the type
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* that this autowired field accepts
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*
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* @param caller
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* calling object
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* @param field
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* field to inject
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*/
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@SuppressWarnings("nls")
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private void handleField(Object caller, Field field)
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throws IllegalStateException, IllegalArgumentException,
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IllegalAccessException {
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if(field.getType().isPrimitive())
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throw new IllegalStateException(String.format(
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"Tried to dependency-inject primative field '%s' of type '%s'",
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field.getName(), field.getType()));
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// field has already been processed, ignore
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if (field.get(caller) != null) {
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return;
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}
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for (AbstractDependencyInjector injector : injectors) {
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Object injection = injector.getInjection(caller, field);
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if (injection != null) {
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field.set(caller, injection);
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return;
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}
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}
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throw new IllegalStateException(
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String.format("No dependency injector found for autowired " +
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"field '%s' in class '%s'. Injectors: %s",
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field.getName(), caller.getClass().getName(),
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Arrays.asList(getInjectors())));
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}
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// --- static methods
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private static DependencyInjectionService instance = null;
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DependencyInjectionService() {
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// prevent instantiation
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}
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/**
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* Gets the singleton instance of the dependency injection service.
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* @return
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*/
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public synchronized static DependencyInjectionService getInstance() {
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if(instance == null)
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instance = new DependencyInjectionService();
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return instance;
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}
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/**
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* Gets the array of installed injectors
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* @return
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*/
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public synchronized AbstractDependencyInjector[] getInjectors() {
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return injectors;
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}
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/**
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* Sets the array of installed injectors
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* @param injectors
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*/
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public synchronized void setInjectors(AbstractDependencyInjector[] injectors) {
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this.injectors = injectors;
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}
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}
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