Some points of Data exchange

 1. SAXBuilder converts an XML file into a JDOM tree

 2. Xpath查询选择节点，newInstance得到xpath对象后selectNodes or selectSingleNode

 3. Publish event 使用 HttpClient，StringTree json 构造eventJsonStr

      JSONWriter writer = new JSONWriter(false);
      Map map = new HashMap();
      map.put("event",eventName);
      map.put("source", event);  
      map.put("param", param);
      String eventJsonStr = writer.write(map);

 4.  JmsTemplate.send(),  创建发送的信息类型 msg = session.createTextMessage();

 5. metaDate 得到表的元数据信息；

     databaseMetaData = conn.getMetaData();
     rs = databaseMetaData.getColumns(null, param.getSchema().toUpperCase(),      

     tableName.toUpperCase(), null);
     while (rs.next()) {
        ColumnBean colb = new ColumnBean();
        colb.setName(rs.getString("COLUMN_NAME"));
        colb.setType(rs.getString("TYPE_NAME"));
        columnBeanList.add(colb);
    }

 6. 三种主流数据库的数据类型对比

Oracle 数据类型	SqlServer 数据类型	MySql数据类型
BLOB	VARBINARY(MAX)	Blob
CHAR	CHAR	Char
CLOB	VARCHAR(MAX)	text
DATE	DATETIME	date
FLOAT	FLOAT	float
INT	NUMERIC(38)	INTEGER
INTERVAL	DATETIME	DATETIME
LONG	VARCHAR(MAX)	text
NUMBER	FLOAT	float
TIMESTAMP	DATETIME	TIMESTAMP
VARCHAR2	VARCHAR	VARCHAR