基于JDBC封装的BaseDao(实例代码)

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});  } 	}