public class BaseDao<T> {

 Connection conn;
 PreparedStatement st;
 ResultSet rs;
 
 JdbcUtil jdbcUtil = new JdbcUtil();
 
 int result = 0;
 
 private Class<T> persistentClass;
 
 @SuppressWarnings("unchecked")
 public BaseDaoUtil(){  
  conn = jdbcUtil.getConnection();
  ParameterizedType type = (ParameterizedType) getClass().getGenericSuperclass();
  persistentClass = (Class<T>) type.getActualTypeArguments()[0];  
 }
 
 
  /**
   * 保存
    * @param entity
   * @return
   */
 public int save(T entity) throws Exception{
  
  String sql = "INSERT INTO "+ entity.getClass().getSimpleName().toLowerCase() +" (";
  
  List<Method> list = this.matchPojoMethods(entity,"get");
  
  Iterator<Method> iter = list.iterator();
   
  Object obj[] = new Object[list.size()];
  int i = 0;
  //拼接字段顺序 insert into table name(id,name,email,
         while(iter.hasNext()) {
            Method method = iter.next();
            sql += method.getName().substring(3).toLowerCase() + ","; 
            if (method.getReturnType().getSimpleName().indexOf("Date") !=-1) {
    SimpleDateFormat sbf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    obj[i] = sbf.format(method.invoke(entity, new Object[]{}));
     }else {
    obj[i] = method.invoke(entity, new Object[]{});
     }     
      i++;
    }
    
    //去掉最后一个,符号insert insert into table name(id,name,email) values(
    sql = sql.substring(0, sql.lastIndexOf(",")) + ") values(";
    
    //拼装预编译SQL语句insert insert into table name(id,name,email) values(?,?,?,
    for(int j = 0; j < list.size(); j++) {
     sql += "?,"; 
    }

    //去掉SQL语句最后一个,符号insert insert into table name(id,name,email) values(?,?,?);
    sql = sql.substring(0, sql.lastIndexOf(",")) + ")";
    
    //到此SQL语句拼接完成,打印SQL语句
    System.out.println(sql);
    
    try {
     st = conn.prepareStatement(sql);
     for (int j = 0; j < obj.length; j++) {
    st.setObject(j+1, obj[j]);
   }
   result = st.executeUpdate();
  } catch (SQLException e) {
   e.printStackTrace();
  }
    
  jdbcUtil.getClose(rs, st, conn);
  
  return result; 
 }
 
 /**
  * 删除
  * @param object
  * @return
  * @throws SQLException
  */
 public int deleteId(Object object) throws Exception{
  
  String sql = "delete from "+ persistentClass.getSimpleName().toLowerCase() +" where ";
  
  //通过子类的构造函数,获得参数化类型的具体类型.比如BaseDAO<T>也就是获得T的具体类型
    T entity = persistentClass.newInstance();
    
    //存放Pojo(或被操作表)主键的方法对象
    Method idMethod = null;
    
    List<Method> list = this.matchPojoMethods(entity, "set");
    Iterator<Method> iter = list.iterator();
    
    //过滤取得Method对象
    while(iter.hasNext()) {
      Method tempMethod = iter.next();
      if(tempMethod.getName().indexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
        idMethod = tempMethod;
      } else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))){
        idMethod = tempMethod;
      }
    }
    //第一个字母转为小写
    sql += idMethod.getName().substring(3,4).toLowerCase()+idMethod.getName().substring(4) + " = ?";
     
  System.out.println(sql);
  
  st = conn.prepareStatement(sql);
  
  //判断id的类型
    if(object instanceof Integer) {
      st.setInt(1, (Integer)object);
    } else if(object instanceof String){
      st.setString(1, (String)object);
    }
  
  result = st.executeUpdate();
  
  jdbcUtil.getClose(rs, st, conn);
  
  return result; 
 }
 
 /**
  * 修改
  * @param entity
  * @return
  * @throws Exception
  */
 public int update(T entity) throws Exception{
  
  String sql = "update "+ entity.getClass().getSimpleName().toLowerCase() +" set ";
  
  List<Method> list = this.matchPojoMethods(entity, "get");
  
  //装载参数
  Object obj[] = new Object[list.size()];
  int i = 0;
  
  //临时Method对象,负责迭代时装method对象.
    Method tempMethod = null;
    
    //由于修改时不需要修改ID,所以按顺序加参数则应该把Id移到最后.
    Method idMethod = null;
    Iterator<Method> iter = list.iterator();
    while(iter.hasNext()) {
      tempMethod = iter.next();
 
      //如果方法名中带有ID字符串并且长度为2,则视为ID.
      if(tempMethod.getName().lastIndexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
       obj[list.size()-1] = tempMethod.invoke(entity, new Object[]{});
        //把ID字段的对象存放到一个变量中,然后在集合中删掉.
        idMethod = tempMethod;
        iter.remove();
      //如果方法名去掉set/get字符串以后与pojo + "id"想符合(大小写不敏感),则视为ID
      } else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))) {
       obj[list.size()-1] = tempMethod.invoke(entity, new Object[]{});
       idMethod = tempMethod;
        iter.remove();        
      }
    }
  
    //把迭代指针移到第一位
    iter = list.iterator();
    while(iter.hasNext()) {
      tempMethod = iter.next();
      sql += tempMethod.getName().substring(3).toLowerCase() + "= ?,";
      obj[i] = tempMethod.invoke(entity, new Object[]{});
      i++;
    }
    
    //去掉最后一个,符号
    sql = sql.substring(0,sql.lastIndexOf(","));
    
    //添加条件
    sql += " where " + idMethod.getName().substring(3).toLowerCase() + " = ?";
    
    //SQL拼接完成,打印SQL语句
    System.out.println(sql);
  
    st = conn.prepareStatement(sql);
    
    for (int j = 0; j < obj.length; j++) {
   st.setObject(j+1, obj[j]);
  }
    
    result = st.executeUpdate();

    jdbcUtil.getClose(rs, st, conn);
    
  return result;

 }
 
 
 public T findById(Object object) throws Exception{
  
  String sql = "select * from "+ persistentClass.getSimpleName().toLowerCase() +" where ";
  
  //通过子类的构造函数,获得参数化类型的具体类型.比如BaseDAO<T>也就是获得T的具体类型
    T entity = persistentClass.newInstance();
    
    //存放Pojo(或被操作表)主键的方法对象
    Method idMethod = null;
    
    List<Method> list = this.matchPojoMethods(entity, "set");
    Iterator<Method> iter = list.iterator();
    
    //过滤取得Method对象
    while(iter.hasNext()) {
      Method tempMethod = iter.next();
      if(tempMethod.getName().indexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
        idMethod = tempMethod;
      } else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))){
        idMethod = tempMethod;
      }
    }
    //第一个字母转为小写
    sql += idMethod.getName().substring(3,4).toLowerCase()+idMethod.getName().substring(4) + " = ?";
     
  System.out.println(sql);
  
  st = conn.prepareStatement(sql);
  
  //判断id的类型
    if(object instanceof Integer) {
      st.setInt(1, (Integer)object);
    } else if(object instanceof String){
      st.setString(1, (String)object);
    }
  
    rs = st.executeQuery();
        
    //把指针指向迭代器第一行
    iter = list.iterator();
    
    //封装
    while(rs.next()) {
      while(iter.hasNext()) {
        Method method = iter.next();
        if(method.getParameterTypes()[0].getSimpleName().indexOf("String") != -1) {
          //由于list集合中,method对象取出的方法顺序与数据库字段顺序不一致(比如:list的第一个方法是setDate,而数据库按顺序取的是"123"值)
          //所以数据库字段采用名字对应的方式取.
          this.setString(method, entity, rs.getString(method.getName().substring(3).toLowerCase()));
        } else if(method.getParameterTypes()[0].getSimpleName().indexOf("Date") != -1){
          this.setDate(method, entity, rs.getDate(method.getName().substring(3).toLowerCase()));
        }else {
          this.setInt(method, entity, rs.getInt(method.getName().substring(3).toLowerCase()));
        }  
      }
    }
  
    jdbcUtil.getClose(rs, st, conn);
    
  return entity;
  
 }
 
 
 
 
 
 /**
   * 过滤当前Pojo类所有带传入字符串的Method对象,返回List集合.
   */
  private List<Method> matchPojoMethods(T entity,String methodName) {
    //获得当前Pojo所有方法对象
    Method[] methods = entity.getClass().getDeclaredMethods();
    
    //List容器存放所有带get字符串的Method对象
    List<Method> list = new ArrayList<Method>();
    
    //过滤当前Pojo类所有带get字符串的Method对象,存入List容器
    for(int index = 0; index < methods.length; index++) {
      if(methods[index].getName().indexOf(methodName) != -1) {
        list.add(methods[index]);
      }
    }    
    return list;
  }
  

  /**
   * 参数类型为String时,为entity字段设置参数,对应set
   */
  public String setString(Method method, T entity, String arg) throws Exception{
    return (String)method.invoke(entity, new Object[]{arg});
  }
  
  
  /**
   * 参数类型为Date时,为entity字段设置参数,对应set
   */
  public Date setDate(Method method, T entity, Date arg) throws Exception{
    return (Date)method.invoke(entity, new Object[]{arg});
  }
 
 
  /**
   * 参数类型为Integer或int时,为entity字段设置参数,对应set
   */
  public Integer setInt(Method method, T entity, Integer arg) throws Exception{
    return (Integer)method.invoke(entity, new Object[]{arg});
  }
  
}