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{
/**
* 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 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 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 : 子类需传入的泛型类型.
*/
public class JdbcDAOImpl implements DAO {
private QueryRunner queryRunner=null;
public Class 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 getForValue(Connection connection, String sql, Object... args)
throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public List 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
}
}
3、编写userDAO来继承这个实现类
package tan.com;
public class userDAO extends JdbcDAOImpl{
}
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");
}
}
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
* @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
* @param
* @param clazz
* @return
*/
@SuppressWarnings("unchecked")
public static Class 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
root
1234
com.mysql.jdbc.Driver
jdbc:mysql:///tan
5
5
5
10
20
5
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。