Dao泛型设计和反射反型

(1)DAO泛型设计：当二哥或多个类中有类似的方法时，可以将这些累死的方法提出到类中，形式一个泛型父类

(2)反射反型：在泛型父类中获取子类的具体类型的过程，叫反射反型

 package cn.itcast.web.generic;

 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import org.apache.commons.dbutils.QueryRunner;
 import org.apache.commons.dbutils.handlers.BeanHandler;
 import cn.itcast.web.util.JdbcUtil;

 //泛型父类
 public class BaseDao<T> {
     private String tableName;
     private Class clazz;
     public BaseDao(){
         //BaseDao<Student>叫参数化类型，ParameterizedType对象
         //获取该类的字节码对象
         Class baseDaoClass = this.getClass();
         //获取Type接口
         Type type = baseDaoClass.getGenericSuperclass();
         //将Type接口强转成ParameterizedType
         ParameterizedType pt = (ParameterizedType) type;
         //获取<Student>类型
         Type[] types = pt.getActualTypeArguments();
         //获取第一个实际参数
         this.clazz = (Class) types[0];
         //根据字节码转成表名
         int index = this.clazz.getName().lastIndexOf(".");
         this.tableName = this.clazz.getName().substring(index+1).toLowerCase();
　　　　　　 System.out.println(clazz.getName());
     }
     /*
     public BaseDao(String tableName, Class clazz) {
         this.tableName = tableName;
         this.clazz = clazz;
     }
     */
     //根据ID查询对象
     public T findById(Integer id) throws Exception{
         T t = null;
         QueryRunner runner = new QueryRunner(JdbcUtil.getDataSource());
         String sql = "select * from " + tableName + " where id = ?";
         Object[] params = {id};
         t = (T) runner.query(sql,new BeanHandler(clazz),params);
         return t;
     }
 }

 //子类
 public class StudentDao extends BaseDao<Student>{
     /*
     public StudentDao(String tableName, Class clazz) {
         super(tableName, clazz);
     }
     */
 }

 package cn.itcast.web.generic;

 import cn.itcast.web.domain.Teacher;

 //子类
 public class TeacherDao extends BaseDao<Teacher>{
     /*
     public TeacherDao(String tableName, Class clazz) {
         super(tableName, clazz);
     }
     */
 }

     @Test
     public void test() {
         TeacherDao tdao=new TeacherDao();
         StudentDao sdao=new StudentDao();
     }