仿照ibatis的风格实现Log，以及添加ConnectionChecker

git-svn-id: http://code.alibabatech.com/svn/druid/trunk@292 b9813039-fb51-4c41-a8b9-e21c2acb5095

src/main/java/com/alibaba/druid/logging/LogFactory.java

@@ -0,0 +1,65 @@
+package com.alibaba.druid.logging;
+
+import java.lang.reflect.Constructor;
+
+public class LogFactory {
+
+    private static Constructor logConstructor;
+
+    static {
+        tryImplementation("org.apache.commons.logging.LogFactory",
+                          "com.ibatis.common.logging.jakarta.JakartaCommonsLoggingImpl");
+        tryImplementation("org.apache.log4j.Logger", "com.ibatis.common.logging.log4j.Log4jImpl");
+        tryImplementation("java.util.logging.Logger", "com.ibatis.common.logging.jdk14.Jdk14LoggingImpl");
+        tryImplementation("java.lang.Object", "com.ibatis.common.logging.nologging.NoLoggingImpl");
+    }
+
+    private static void tryImplementation(String testClassName, String implClassName) {
+        if (logConstructor == null) {
+            try {
+                Resources.classForName(testClassName);
+                Class implClass = Resources.classForName(implClassName);
+                logConstructor = implClass.getConstructor(new Class[] { Class.class });
+            } catch (Throwable t) {
+            }
+        }
+    }
+
+    public static Log getLog(Class aClass) {
+        try {
+            return (Log) logConstructor.newInstance(new Object[] { aClass });
+        } catch (Throwable t) {
+            throw new RuntimeException("Error creating logger for class " + aClass + ".  Cause: " + t, t);
+        }
+    }
+
+    /**
+     * This method will switch the logging implementation to Log4J if Log4J is available on the classpath. This is
+     * useful in situations where you want to use Log4J to log iBATIS activity but commons logging is on the classpath.
+     * Note that this method is only effective for log classes obtained after calling this method. If you intend to use
+     * this method you should call it before calling any other iBATIS method.
+     */
+    public static synchronized void selectLog4JLogging() {
+        try {
+            Resources.classForName("org.apache.log4j.Logger");
+            Class implClass = Resources.classForName("com.ibatis.common.logging.log4j.Log4jImpl");
+            logConstructor = implClass.getConstructor(new Class[] { Class.class });
+        } catch (Throwable t) {
+        }
+    }
+
+    /**
+     * This method will switch the logging implementation to Java native logging if you are running in JRE 1.4 or above.
+     * This is useful in situations where you want to use Java native logging to log iBATIS activity but commons logging
+     * or Log4J is on the classpath. Note that this method is only effective for log classes obtained after calling this
+     * method. If you intend to use this method you should call it before calling any other iBATIS method.
+     */
+    public static synchronized void selectJavaLogging() {
+        try {
+            Resources.classForName("java.util.logging.Logger");
+            Class implClass = Resources.classForName("com.ibatis.common.logging.jdk14.Jdk14LoggingImpl");
+            logConstructor = implClass.getConstructor(new Class[] { Class.class });
+        } catch (Throwable t) {
+        }
+    }
+}