Initial commit for "Spring Custom Annotation with Dynamic Qualifier"

article.

spring-all/src/main/java/org/baeldung/customannotation/DataAccessFieldCallback.java

@@ -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;
+    }
+}