几种通过JDBC操作数据库的方法，以及返回数据的处理

1.SQL TO String ：只返回一个查询结果

　　例如查询某条记录的总数

rs =
stmt.executeQuery(replacedCommand);
            
if (rs != null && rs.next()) // rs only contains one row and one
column
            
{
                   
String tempStr =
rs.getString(1);
                   
if (tempStr ==
null)
                   
{
                       
result =
"";
                   
}
else
                   
{
                       
result =
rs.getString(1);
                   
}

　　　　}

2.SQL TO Object :返回的是类似某个对象的记录，即很多条字段

　　例如，查询某个用户的所有订单，并反射到对象中去

　　className 为你要映射的对象的名字

Document
xmlContentDoc =
null;
          
OracleXMLQuery
xmlQuery;
            
rs = stmt.executeQuery(replacedCommand);

xmlQuery = new OracleXMLQuery(conn,
rs);
            
xmlQuery.setRowTag(className);
             
xmlContentDoc =
xmlQuery.getXMLDOM();
           
checkDocumentErrors(xmlContentDoc,
xmlQuery.ERROR_TAG);
           

           
TransformerFactory tFactory =
TransformerFactory.newInstance();
           
Transformer
transformer=null;
           
DOMSource
source=null;
           
StreamResult
result=null;
           
transformer =
tFactory.newTransformer();
              

            //get all
tags with class name equal to
"className"
           
NodeList
rows=xmlContentDoc.getElementsByTagName(className);
        

            //loop on
the row and make objects that map to the selected row
elements
           
for(int
i=0;i<rows.getLength();i++)
           
{
               
Element row =
(Element)rows.item(i);
               
row.removeAttribute("num");             

               
StringWriter sw=new
StringWriter();
               
source = new
DOMSource(row);
               
result = new
StreamResult(sw);
               
transformer.transform(source,
result);
               
String
xmlString=sw.toString();
               
sw.close();               

               
Object
inputObj=Class.forName(className).newInstance();
               
Converter
converter=Converter.getInstance();       

               
Object
OutputObj=converter.convertToObject(xmlString,inputObj);
               
outputResult.add(OutputObj);
           
}

3.SQL TO Map:这种查询的是2个字段，其中一个作为key,另一个字段作为value

rs =
stmt.executeQuery(replacedCommand);
             
if(rs !=
null)
             
{                                      

                   
ResultSetMetaData
metadata;
                   
int coloumnNo =
0;                   

                   
metadata =
rs.getMetaData();
                   
coloumnNo =
metadata.getColumnCount();
                   
Object
tempKey,tempValue;
                   
while(rs.next())
                   
{
                       
//if the number of coloumns =1 make the in the hashtable the key and value are
the
same                     

                       
if(coloumnNo ==
1)
                       
{          

                           
tempKey=rs.getObject(1);                           

                           
if(tempKey==null)  
tempKey="";
                           
tempValue=tempKey;
                           
tempKey= (tempKey instanceof CLOB) ? rs.getString(1) :
tempKey.toString().trim();
                           
tempValue=tempKey;
                           
result.put(tempKey,tempValue);                           

                       
}else
                       
{                           

                           
tempKey=rs.getObject(1);
                           
tempValue=rs.getObject(2);
                           
if(tempKey==null)  
tempKey="";
                           
if(tempValue==null)  
tempValue="";
                           
tempKey=(tempKey instanceof CLOB) ? rs.getString(1) :
tempKey.toString().trim();
                           
tempValue=(tempValue instanceof CLOB) ? rs.getString(2) :
tempValue.toString().trim();
                           
result.put(tempKey,tempValue);
                       
}//else                   

                   
}//while              

             
}

4.  明天待续！

几种通过JDBC操作数据库的方法，以及返回数据的处理