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[utils] / support / general / src / main / java / org / wamblee / ioc / BeanKernel.java

diff --git a/support/general/src/main/java/org/wamblee/ioc/BeanKernel.java b/support/general/src/main/java/org/wamblee/ioc/BeanKernel.java
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+/*
+ * Copyright 2005-2010 the original author or authors.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */ 
+package org.wamblee.ioc;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.wamblee.io.ClassPathResource;
+import org.wamblee.io.InputResource;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import java.util.Properties;
+
+/**
+ * The standard means to obtain the bean factory. This works by reading a
+ * property {@value #BEAN_FACTORY_CLASS} from a property file named
+ * {@value #BEAN_KERNEL_PROP_FILE} from the class path. This property identifies
+ * the bean factory implementation to use. The configured bean factory must have
+ * a no-arg constructor.
+ */
+public final class BeanKernel {
+    private static final Log LOG = LogFactory.getLog(BeanKernel.class);
+
+    /**
+     * Bean factory kernel properties file.
+     */
+    private static final String BEAN_KERNEL_PROP_FILE = "org.wamblee.beanfactory.properties";
+
+    /**
+     * Name of the property to define the name of the bean factory class to use.
+     * THis class must have a public default constructor.
+     */
+    private static final String BEAN_FACTORY_CLASS = "org.wamblee.beanfactory.class";
+
+    /**
+     * Cached bean factory.
+     */
+    private static BeanFactory BEAN_FACTORY;
+
+    /**
+     * Disabled constructor.
+     * 
+     */
+    private BeanKernel() {
+        // Empty
+    }
+
+    /**
+     * Overrides the default mechanism for looking up the bean factory by
+     * specifying it yourself.
+     * 
+     * @param aOverride
+     *            Override bean factory.
+     */
+    public static void overrideBeanFactory(BeanFactory aOverride) {
+        BEAN_FACTORY = aOverride;
+    }
+
+    /**
+     * Gets the bean factory.
+     * 
+     * @return Bean factory.
+     */
+    public static BeanFactory getBeanFactory() {
+        synchronized (BeanFactory.class) {
+            if (BEAN_FACTORY == null) {
+                BEAN_FACTORY = lookupBeanFactory(BEAN_KERNEL_PROP_FILE);
+            }
+        }
+
+        return BEAN_FACTORY;
+    }
+
+    /**
+     * Lookup the bean factory based on the properties file.
+     * 
+     * 
+     * @return Bean factory.
+     * 
+     */
+    static BeanFactory lookupBeanFactory(String aPropertyFilename) {
+        InputResource resource = new ClassPathResource(aPropertyFilename);
+        InputStream is;
+
+        try {
+            is = resource.getInputStream();
+        } catch (IOException e) {
+            throw new BeanFactoryException("Cannot open resource " + resource,
+                e);
+        }
+
+        try {
+            Properties props = new Properties();
+            props.load(is);
+
+            String className = props.getProperty(BEAN_FACTORY_CLASS);
+            Class beanFactory = Class.forName(className);
+
+            return (BeanFactory) beanFactory.newInstance();
+        } catch (Exception e) {
+            throw new BeanFactoryException("Cannot read from resource " +
+                resource, e);
+        } finally {
+            try {
+                is.close();
+            } catch (IOException e) {
+                // last resort cannot do much now.
+                LOG.error("Error closing resource " + resource);
+            }
+        }
+    }
+}