Initial commit for "Spring Custom Annotation with Dynamic Qualifier"

article.
2015-10-21 00:50:44 +07:00
parent 6aec841b73
commit 32ea1e0a1e
10 changed files with 394 additions and 0 deletions
@@ -0,0 +1,9 @@
+package org.baeldung.customannotation;
+
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+@ComponentScan("org.baeldung.customannotation")
+public class CustomAnnotationConfiguration {
+}
@@ -0,0 +1,14 @@
+package org.baeldung.customannotation;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
+@Documented
+public @interface DataAccess {
+    Class<?>entity();
+}
@@ -0,0 +1,39 @@
+package org.baeldung.customannotation;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.stereotype.Component;
+import org.springframework.util.ReflectionUtils;
+import org.springframework.util.ReflectionUtils.FieldCallback;
+
+@Component
+public class DataAccessAnnotationProcessor implements BeanPostProcessor {
+
+    private ConfigurableListableBeanFactory configurableListableBeanFactory;
+
+    @Autowired
+    public DataAccessAnnotationProcessor(ConfigurableListableBeanFactory bf) {
+        configurableListableBeanFactory = bf;
+    }
+
+    @Override
+    public Object postProcessBeforeInitialization(Object bean, String beanName) 
+    throws BeansException {
+        scanDataAccessAnnotation(bean, beanName);
+        return bean;
+    }
+
+    @Override
+    public Object postProcessAfterInitialization(Object bean, String beanName) 
+    throws BeansException {
+        return bean;
+    }
+
+    protected void scanDataAccessAnnotation(Object bean, String beanName) {
+        Class<?> managedBeanClass = bean.getClass();
+        FieldCallback fcb = new DataAccessFieldCallback(configurableListableBeanFactory, bean);
+        ReflectionUtils.doWithFields(managedBeanClass, fcb);
+    }
+}
@@ -0,0 +1,104 @@
+package org.baeldung.customannotation;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.util.ReflectionUtils;
+import org.springframework.util.ReflectionUtils.FieldCallback;
+
+
+public final class DataAccessFieldCallback implements FieldCallback {
+
+    private static Logger logger = LoggerFactory.getLogger(DataAccessFieldCallback.class);
+    private static int AUTOWIRE_MODE = AutowireCapableBeanFactory.AUTOWIRE_BY_NAME;
+
+    private static String ERROR_ENTITY_VALUE_NOT_SAME = "@DataAccess(entity) "
+            + "value should have same type with injected generic type.";
+    private static String WARN_NON_GENERIC_VALUE = "@DataAccess annotation assigned "
+            + "to raw (non-generic) declaration. This will make your code less type-safe.";
+    private static String ERROR_CREATE_INSTANCE = "Cannot create instance of "
+            + "type '{}' or instance creation is failed because: {}";
+
+    private ConfigurableListableBeanFactory configurableListableBeanFactory;
+    private Object bean;
+
+    public DataAccessFieldCallback(final ConfigurableListableBeanFactory bf, final Object bean) {
+        configurableListableBeanFactory = bf;
+        this.bean = bean;
+    }
+
+    @Override
+    public void doWith(final Field field) 
+    throws IllegalArgumentException, IllegalAccessException {
+        if (!field.isAnnotationPresent(DataAccess.class)) {
+            return;
+        }
+        ReflectionUtils.makeAccessible(field);
+        final Type fieldGenericType = field.getGenericType();
+       // In this example, get actual "GenericDAO' type.
+        final Class<?> generic = field.getType(); 
+        final Class<?> classValue = field.getDeclaredAnnotation(DataAccess.class).entity();
+
+        if (genericTypeIsValid(classValue, fieldGenericType)) {
+            final String beanName = classValue.getSimpleName() + generic.getSimpleName();
+            final Object beanInstance = getBeanInstance(beanName, generic, classValue);
+            field.set(bean, beanInstance);
+        } else {
+            throw new IllegalArgumentException(ERROR_ENTITY_VALUE_NOT_SAME);
+        }
+    }
+
+
+    /**
+     * For example, if user write:
+     * <pre>
+     * &#064;DataAccess(entity=Person.class) 
+     * private GenericDAO&lt;Account&gt; personGenericDAO;
+     * </pre>
+     * then this is should be failed.
+     */
+    public boolean genericTypeIsValid(final Class<?> clazz, final Type field) {
+        if (field instanceof ParameterizedType) {
+            final ParameterizedType parameterizedType = (ParameterizedType) field;
+            final Type type = parameterizedType.getActualTypeArguments()[0];
+
+            return type.equals(clazz);
+        } else {
+            logger.warn(WARN_NON_GENERIC_VALUE);
+            return true;
+        }
+    }
+
+
+
+    public final Object getBeanInstance(final String beanName, final Class<?> genericClass, final Class<?> paramClass) {
+        Object daoInstance = null;
+        if (!configurableListableBeanFactory.containsBean(beanName)) {
+            logger.info("Creating new DataAccess bean named '{}'.", beanName);
+
+            Object toRegister = null;
+            try {
+                final Constructor<?> ctr = genericClass.getConstructor(Class.class);
+                toRegister = ctr.newInstance(paramClass);
+            } catch (final Exception e) {
+                logger.error(ERROR_CREATE_INSTANCE, genericClass.getTypeName(), e);
+                throw new RuntimeException(e);
+            }
+            
+            daoInstance = configurableListableBeanFactory.initializeBean(toRegister, beanName);
+            configurableListableBeanFactory.autowireBeanProperties(daoInstance, AUTOWIRE_MODE, true);
+            configurableListableBeanFactory.registerSingleton(beanName, daoInstance);
+            logger.info("Bean named '{}' created successfully.", beanName);
+        } else {
+            daoInstance = configurableListableBeanFactory.getBean(beanName);
+            logger.info("Bean named '{}' already exist used as current bean reference.", beanName);
+        }
+        return daoInstance;
+    }
+}
@@ -0,0 +1,30 @@
+package org.baeldung.customannotation;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+
+public class GenericDAO<E> {
+
+    private Class<E> entityClass;
+    private String message;
+
+    public GenericDAO(Class<E> entityClass) {
+        this.entityClass = entityClass;
+    }
+
+    public List<E> findAll() {
+        message = "Would create findAll query from " + entityClass.getSimpleName();
+        return Collections.emptyList();
+    }
+
+    public Optional<E> persist(E toPersist) {
+        message = "Would create persist query from " + toPersist.getClass().getSimpleName();
+        return Optional.empty();
+    }
+
+    /** Only used for unit-testing. */
+    public final String getMessage() {
+        return message;
+    }
+}