hal/src/zutil/db/bean/DBBeanSQLResultHandler.java

package zutil.db.bean;

import java.lang.reflect.Field;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.ResultSet;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.logging.Logger;

import zutil.db.DBConnection;
import zutil.db.SQLResultHandler;
import zutil.db.bean.DBBean.DBBeanConfig;
import zutil.db.bean.DBBean.DBLinkTable;
import zutil.log.LogUtil;

public class DBBeanSQLResultHandler<T> implements SQLResultHandler<T>{
	public static final Logger logger = LogUtil.getLogger();
	/** This is the time to live for the cached items **/
	public static final long CACHE_TTL = 1000*60*10; // in ms
	/** A cache for detecting recursion **/
	protected static HashMap<Class<?>, HashMap<Object,DBBeanCache>> cache =
		new HashMap<Class<?>, HashMap<Object,DBBeanCache>>();
	/**
	 * A cache container that contains a object and last read time
	 */
	protected static class DBBeanCache{
		public long timestamp;
		public DBBean bean;
	}
	
	private Class<? extends DBBean> bean_class;
	private DBBeanConfig bean_config;
	private DBConnection db;
	private boolean list;

	/**
	 * Creates a new instance of this class that returns only one bean
	 * 
	 * @param 	cl		is the DBBean class that will be parsed from the SQL result
	 * @return			a new instance of this class
	 */
	public static <C extends DBBean> DBBeanSQLResultHandler<C> create(Class<C> cl){		
		return new DBBeanSQLResultHandler<C>(cl, null, false);
	}

	/**
	 * Creates a new instance of this class that returns a bean with all its containing beans
	 * 
	 * @param 	cl		is the DBBean class that will be parsed from the SQL result
	 * @param	db		is the DB connection for loading internal beans
	 * @return			a new instance of this class
	 */
	public static <C extends DBBean> DBBeanSQLResultHandler<C> create(Class<C> cl, DBConnection db){		
		return new DBBeanSQLResultHandler<C>(cl, db, false);
	}

	/**
	 * Creates a new instance of this class that returns a list of beans
	 * 
	 * @param 	cl		is the DBBean class that will be parsed from the SQL result
	 * @return			a new instance of this class
	 */
	public static <C extends DBBean> DBBeanSQLResultHandler<List<C>> createList(Class<C> cl){
		return new DBBeanSQLResultHandler<List<C>>(cl, null, true);
	}

	/**
	 * Creates a new instance of this class that returns a list of beans with all the internal beans
	 * 
	 * @param 	cl		is the DBBean class that will be parsed from the SQL result
	 * @param	db		is the DB connection for loading internal beans
	 * @return			a new instance of this class
	 */
	public static <C extends DBBean> DBBeanSQLResultHandler<List<C>> createList(Class<C> cl, DBConnection db){
		return new DBBeanSQLResultHandler<List<C>>(cl, db, true);
	}

	/**
	 * Creates a new instance of this class
	 * 
	 * @param 	cl		is the DBBean class that will be parsed from the SQL result
	 * @param	db		is the DB connection for loading internal beans, may be null to disable internal beans
	 * @param	list	is if the handler should return a list of beans instead of one
	 */
	protected DBBeanSQLResultHandler(Class<? extends DBBean> cl, DBConnection db, boolean list) {
		this.bean_class = cl;
		this.list = list;
		this.db = db;
		this.bean_config = DBBean.getBeanConfig( cl );
	}

	/**
	 * Is called to handle an result from an query.
	 * 
	 * @param stmt 		is the query
	 * @param result 	is the ResultSet
	 */
	@SuppressWarnings("unchecked")
	public T handleQueryResult(Statement stmt, ResultSet result) throws SQLException{
		if( list ){
			LinkedList<DBBean> bean_list = new LinkedList<DBBean>();
			while( result.next() ){
				DBBean obj = createBean(result);
				bean_list.add( obj );
			}
			return (T) bean_list;
		}
		else{
			if( result.next() )
				return (T) createBean(result);
			return null;
		}

	}

	/**
	 * Instantiates a new bean and assigns field values from the ResultSet
	 * 
	 * @param 	result	is where the field values for the bean will bee read from, the cursor should be in front of the data
	 * @return			a new instance of the bean
	 */
	@SuppressWarnings("unchecked")
	private DBBean createBean(ResultSet result) throws SQLException{
		try {			
			Object id = result.getObject( bean_config.id_field.getName() );
			DBBean obj = getCachedDBBean(bean_class, id);
			if( obj != null )
				return obj;
			obj = bean_class.newInstance();
			cacheDBBean(obj, id);
			
			// Get id field
			obj.setFieldValue(bean_config.id_field, result.getLong(bean_config.id_field.getName()));
			// Get the rest
			for( Field field : bean_config.fields ){
				// Skip id field (its already loaded)
				if( field.equals(bean_config.id_field) )
					continue;
				String name = field.getName();

				// Another DBBean class
				if( DBBean.class.isAssignableFrom( field.getType() )){
					if(db != null){
						Object subid = result.getObject(name);
						DBBean subobj = getCachedDBBean(field.getType(), subid);
						if( subobj == null )
							subobj = DBBean.load(db, (Class<? extends DBBean>)field.getType(), subid);
						obj.setFieldValue(field, subobj);
					}
				}
				// A list of DBBeans
				else if( List.class.isAssignableFrom( field.getType() ) && 
						field.getAnnotation( DBLinkTable.class ) != null){
					if(db != null){
						DBLinkTable linkTable = field.getAnnotation( DBLinkTable.class );
						String subtable = linkTable.name();
						String idcol = (linkTable.column().isEmpty() ? bean_config.tableName : linkTable.column() );

						// Load list from link table
						PreparedStatement subStmt = db.getPreparedStatement("SELECT * FROM "+subtable+" WHERE ?=?");
						subStmt.setString(1, idcol);
						subStmt.setObject(2, bean_config.id_field.get( obj ));
						List<? extends DBBean> list = DBConnection.exec(subStmt, 
								DBBeanSQLResultHandler.createList(linkTable.beanClass(), db));
						obj.setFieldValue(field, list);
					}
				}
				// Normal field
				else				
					obj.setFieldValue(field, result.getObject(name));
			}
			return obj;

		} catch (InstantiationException e) {
			throw new SQLException(e);
		} catch (IllegalAccessException e) {
			throw new SQLException(e);
		}
	}

	/**
	 * Adds the given object to the cache
	 * 
	 * @param obj	is the object to cache
	 * @param id	is the id object of the bean
	 */
	protected static void cacheDBBean(DBBean obj, Object id) {
		DBBeanCache item = new DBBeanCache();
		item.timestamp = System.currentTimeMillis();
		item.bean = obj;
		if( cache.containsKey(obj.getClass()) )
			cache.get(obj.getClass()).put(id, item);
		else{
			HashMap<Object, DBBeanCache> map = new HashMap<Object, DBBeanCache>();
			map.put(id, item);
			cache.put(obj.getClass(), map);
		}
	}

	/**
	 * @param c		is the class of the bean
	 * @param id	is the id object of the bean
	 * @return		an cached DBBean object or null if the object is not cached or has expired
	 */
	protected static DBBean getCachedDBBean(Class<?> c, Object id){
		if( cache.containsKey(c) ){
			DBBeanCache item = cache.get(c).get(id);
			// Check if the cache is valid
			if( item != null &&  item.timestamp+CACHE_TTL > System.currentTimeMillis() ){
				return item.bean;
			}
			// The cache is old, remove it and return null
			else{
				logger.finer("Cache to old: "+c.getName()+" ID: "+id);
				cache.get(c).remove(id);
				return null;
			}
		}
		logger.finer("Cache miss: "+c.getName()+" ID: "+id);
		return null;
	}
	
}