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; }
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()); } @Override public void batch(Connection connection, String sql, Object[]... args) throws SQLException { // TODO Auto-generated method stub } @Override public <E> E getForValue(Connection connection, String sql, Object... args) throws SQLException { // TODO Auto-generated method stub return null; } @Override public List<T> getForList(Connection connection, String sql, Object... args) throws SQLException { // TODO Auto-generated method stub return null; } @Override public T get(Connection connection, String sql, Object... args) throws SQLException { return queryRunner.query(connection, sql, new BeanHandler<>(type), args); } @Override public void update(Connection connection, String sql, Object... args) throws SQLException { // TODO Auto-generated method stub } }
package tan.com; public class userDAO extends JdbcDAOImpl<user>{ }
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(); @Test public void testBatch() { fail("Not yet implemented"); } @Test public void testGetForValue() { fail("Not yet implemented"); } @Test public void testGetForList() { fail("Not yet implemented"); } @Test public 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); } } @Test public void testUpdate() { fail("Not yet implemented"); } }
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; } }
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(); } } } }
<?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>
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。