[java] Check if table exists

之前是用 sql 去查，但會有 sql server / mysql / sqlite … 等多重 server 的問題，另一個較好的解法：

You can use the available meta data:

  DatabaseMetaData meta = con.getMetaData();
  ResultSet res = meta.getTables(null, null, "My_Table_Name", 
     new String[] {"TABLE"});
  while (res.next()) {
     System.out.println(
        "   "+res.getString("TABLE_CAT") 
       + ", "+res.getString("TABLE_SCHEM")
       + ", "+res.getString("TABLE_NAME")
       + ", "+res.getString("TABLE_TYPE")
       + ", "+res.getString("REMARKS")); 
  }

See here for more details. Note also the caveats in the JavaDoc.