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();
    }