使用DBUtils编写通用的DAO【很有价值】

1、定义DAO接口（便于各个版本来实现）

package tan.com;import java.sql.Connection;import java.sql.SQLException;import java.util.List;/** * 访问数据的 DAO 接口. 在里面定义好访问数据表的各种方法 * @param T: DAO 处理的实体类的类型 *  * */public interface DAO<T>{/** * 批量处理的方法 * @param connection * @param sql * @param args: 填充占位符的 Object [] 类型的可变参数. * @throws SQLException  */  void batch(Connection connection, String sql, Object [] ... args) throws SQLException;/** * 返回具体的一个值, 例如总人数, 平均工资, 某一个人的 email 等. * @param connection * @param sql * @param args * @return * @throws SQLException  */<E> E getForValue(Connection connection,String sql, Object ... args) throws SQLException;/** * 返回 T 的一个集合 * @param connection * @param sql * @param args * @return * @throws SQLException  */List<T> getForList(Connection connection,String sql,Object ...args)throws SQLException;/** * 返回一个 T 的对象 * @param connection * @param sql * @param args * @return * @throws SQLException  */T get(Connection connection,String sql,Object ...args)throws SQLException;/** * INSRET, UPDATE, DELETE * @param connection: 数据库连接 * @param sql: SQL 语句 * @param args: 填充占位符的可变参数. * @throws SQLException  *  */void update(Connection connection,String sql,Object ...args)throws SQLException;}

2、编写DAO的实现类JdbcDaoImpl.java

package tan.com;import java.sql.Connection;import java.sql.SQLException;import java.util.List;import org.apache.commons.dbutils.QueryRunner;import org.apache.commons.dbutils.handlers.BeanHandler;/** * 使用 QueryRunner 提供其具体的实现 * @param <T>: 子类需传入的泛型类型.  */public class JdbcDAOImpl<T> implements DAO<T> {private QueryRunner queryRunner=null;public Class<T> type;public JdbcDAOImpl(){queryRunner=new QueryRunner();type=ReflectionUtils.getSuperGenericType(getClass());}@Overridepublic void batch(Connection connection, String sql, Object[]... args)throws SQLException {// TODO Auto-generated method stub}@Overridepublic <E> E getForValue(Connection connection, String sql, Object... args)throws SQLException {// TODO Auto-generated method stubreturn null;}@Overridepublic List<T> getForList(Connection connection, String sql, Object... args)throws SQLException {// TODO Auto-generated method stubreturn null;}@Overridepublic T get(Connection connection, String sql, Object... args)throws SQLException {return queryRunner.query(connection, sql,new BeanHandler<>(type), args);}@Overridepublic void update(Connection connection, String sql, Object... args)throws SQLException {// TODO Auto-generated method stub}}

3、编写userDAO来继承这个实现类

package tan.com;public class userDAO extends JdbcDAOImpl<user>{}

4、编写单元测试类

package tan.com;import static org.junit.Assert.*;import java.sql.Connection;import java.sql.SQLException;import org.junit.Test;public class userDaoTest {userDAO dao=new userDAO();@Testpublic void testBatch() {fail("Not yet implemented");}@Testpublic void testGetForValue() {fail("Not yet implemented");}@Testpublic void testGetForList() {fail("Not yet implemented");}@Testpublic void testGet() throws SQLException {Connection connection=null;try {connection=JDBCTools.getConnection();String sql="SELECT id, name,age,school " +"FROM user " +"WHERE id = ?"; user user1=dao.get(connection, sql, 5); System.out.println(user1);} catch (Exception e) {e.printStackTrace();}finally{JDBCTools.release(null, null, connection);}}@Testpublic void testUpdate() {fail("Not yet implemented");}}

5、利用反射工具类获取类型

package tan.com;import java.lang.reflect.Field;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.lang.reflect.Modifier;import java.lang.reflect.ParameterizedType;import java.lang.reflect.Type;/** * 反射的 Utils 函数集合 * 提供访问私有变量, 获取泛型类型 Class, 提取集合中元素属性等 Utils 函数 * @author Administrator * */public class ReflectionUtils {/** * 通过反射, 获得定义 Class 时声明的父类的泛型参数的类型 * 如: public EmployeeDao extends BaseDao<Employee, String> * @param clazz * @param index * @return */@SuppressWarnings("unchecked")public static Class getSuperClassGenricType(Class clazz, int index){Type genType = clazz.getGenericSuperclass();if(!(genType instanceof ParameterizedType)){return Object.class;}Type [] params = ((ParameterizedType)genType).getActualTypeArguments();if(index >= params.length || index < 0){return Object.class;}if(!(params[index] instanceof Class)){return Object.class;}return (Class) params[index];}/** * 通过反射, 获得 Class 定义中声明的父类的泛型参数类型 * 如: public EmployeeDao extends BaseDao<Employee, String> * @param <T> * @param clazz * @return */@SuppressWarnings("unchecked")public static<T> Class<T> getSuperGenericType(Class clazz){return getSuperClassGenricType(clazz, 0);}/** * 循环向上转型, 获取对象的 DeclaredMethod * @param object * @param methodName * @param parameterTypes * @return */public static Method getDeclaredMethod(Object object, String methodName, Class<?>[] parameterTypes){for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){try {//superClass.getMethod(methodName, parameterTypes);return superClass.getDeclaredMethod(methodName, parameterTypes);} catch (NoSuchMethodException e) {//Method 不在当前类定义, 继续向上转型}//..}return null;}/** * 使 filed 变为可访问 * @param field */public static void makeAccessible(Field field){if(!Modifier.isPublic(field.getModifiers())){field.setAccessible(true);}}/** * 循环向上转型, 获取对象的 DeclaredField * @param object * @param filedName * @return */public static Field getDeclaredField(Object object, String filedName){for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){try {return superClass.getDeclaredField(filedName);} catch (NoSuchFieldException e) {//Field 不在当前类定义, 继续向上转型}}return null;}/** * 直接调用对象方法, 而忽略修饰符(private, protected) * @param object * @param methodName * @param parameterTypes * @param parameters * @return * @throws InvocationTargetException  * @throws IllegalArgumentException  */public static Object invokeMethod(Object object, String methodName, Class<?> [] parameterTypes,Object [] parameters) throws InvocationTargetException{Method method = getDeclaredMethod(object, methodName, parameterTypes);if(method == null){throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + object + "]");}method.setAccessible(true);try {return method.invoke(object, parameters);} catch(IllegalAccessException e) {System.out.println("不可能抛出的异常");} return null;}/** * 直接设置对象属性值, 忽略 private/protected 修饰符, 也不经过 setter * @param object * @param fieldName * @param value */public static void setFieldValue(Object object, String fieldName, Object value){Field field = getDeclaredField(object, fieldName);if (field == null)throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");makeAccessible(field);try {field.set(object, value);} catch (IllegalAccessException e) {System.out.println("不可能抛出的异常");}}/** * 直接读取对象的属性值, 忽略 private/protected 修饰符, 也不经过 getter * @param object * @param fieldName * @return */public static Object getFieldValue(Object object, String fieldName){Field field = getDeclaredField(object, fieldName);if (field == null)throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");makeAccessible(field);Object result = null;try {result = field.get(object);} catch (IllegalAccessException e) {System.out.println("不可能抛出的异常");}return result;}}

6、利用到JDBCTools.java工具类

package tan.com;import java.sql.Connection;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import javax.sql.DataSource;import com.mchange.v2.c3p0.ComboPooledDataSource;public class JDBCTools {//数据库连接池应该只被初始化一次（多个项目共享一个连接池就够了）private static DataSource dataSource=null;static{dataSource=new ComboPooledDataSource("helloc3p0");}//获取数据库连接的方法public static Connection getConnection() throws Exception{return dataSource.getConnection();}    /**     * 2、关闭资源     * 关闭资源关闭 Statement 和 Connection和ResultSet     * @param rs     * @param statement     * @param conn     */public static void release(ResultSet rs, Statement statement, Connection conn) {if(rs != null){try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if (statement != null) {try {statement.close();} catch (Exception e2) {e2.printStackTrace();}}if (conn != null) {try {conn.close();} catch (Exception e2) {e2.printStackTrace();}}}/** * 关闭 Statement 和 Connection * @param statement * @param conn */public static void release(Statement statement, Connection conn) {if (statement != null) {try {statement.close();} catch (Exception e2) {e2.printStackTrace();}}if (conn != null) {try {conn.close();} catch (Exception e2) {e2.printStackTrace();}}}}

7、c3p0数据库配置同上

<?xml version="1.0" encoding="UTF-8"?><c3p0-config><named-config name="helloc3p0"><!-- 指定连接数据源的基本属性 --><property name="user">root</property><property name="password">1234</property><property name="driverClass">com.mysql.jdbc.Driver</property><property name="jdbcUrl">jdbc:mysql:///tan</property><!-- 若数据库中连接数不足时, 一次向数据库服务器申请多少个连接 --><property name="acquireIncrement">5</property><!-- 初始化数据库连接池时连接的数量 --><property name="initialPoolSize">5</property><!-- 数据库连接池中的最小的数据库连接数 --><property name="minPoolSize">5</property><!-- 数据库连接池中的最大的数据库连接数 --><property name="maxPoolSize">10</property><!-- C3P0 数据库连接池可以维护的 Statement 的个数 --><property name="maxStatements">20</property><!-- 每个连接同时可以使用的 Statement 对象的个数 --><property name="maxStatementsPerConnection">5</property></named-config></c3p0-config>

测试结果：

整个方法实现流程：

虽说最终出来结果了，但我还是没能全部理解，特此记下以便日后查看。