Jdbc--dao design mode

1, DAO (data access Object): A class that accesses data information, contains a crud (Create, Read, Update, Delete) on the data, and does not contain any business-related information.

--dao can realize the modularization of function;

-facilitates the maintenance and upgrading of code.

2. Common methods in DAO:

--1) int update (String sql, Object ... args); Performs an update operation that returns the number of rows affected, including INSERT, UPDATE, delete operations.

--2) <T> T get (class<t> clazz, String sql, Object ... args); Queries a record to return the corresponding object.

--3) <T> list<t> getforlist (class<t> clazz, String sql, objeect ... args); Queries multiple records, returning the corresponding list of objects.

--4) <E> E getforvalue (String sql, Object ... args); Returns the value of a field in a record or the number of records for a statistic.

3. Realize:

 Public classDAO { Public intUpdate (String sql, Object ... args) {Connection conn=NULL; PreparedStatement PS=NULL; intRowNum = 0; Try{conn=jdbcutils.getconnection (); PS=conn.preparestatement (SQL);  for(inti = 0; i < args.length; i++) {Ps.setobject (i+ 1, Args[i]); } rowNum=ps.executeupdate (); returnRowNum; }Catch(Exception e) {e.printstacktrace (); }finally{jdbcutils.release (conn, PS,NULL); }        returnRowNum; }         Public<T> T Get (class<t>clazz, String sql, Object ... args) {T entity=NULL; Connection Conn=NULL; PreparedStatement PS=NULL; ResultSet RS=NULL; Try{conn=jdbcutils.getconnection (); PS=conn.preparestatement (SQL);  for(inti = 0; i < args.length; i++) {Ps.setobject (i+ 1, Args[i]); } RS=Ps.executequery (); Map<string, object> map =NewHashmap<string, object>(); List<String> Columnlabels =Getcolumnlabels (RS); if(Rs.next ()) { for(String columnlabel:columnlabels) {Object Columnvalue=Rs.getobject (ColumnLabel);                Map.put (ColumnLabel, Columnvalue); }            }                        if(Map.size () > 0) {Entity=clazz.newinstance ();  for(Map.entry<string, object>Entry:map.entrySet ()) {String FieldName=Entry.getkey (); Object value=Entry.getvalue (); //Use the Beanutils tool class to assign a value to a propertyBeanutils.setproperty (Entity, fieldName, value); /**assign a value to a property using reflection field field = Clazz.getdeclaredfield (key);                    Field.setaccessible (TRUE); Field.set (entity, value);*/                }                returnentity; }                    }Catch(Exception e) {e.printstacktrace (); }finally{jdbcutils.release (conn, PS, RS); }        returnentity; }         Public<T> list<t> getforlist (class<t>clazz, String sql, Object ... args) {List<T> list =NewArraylist<>(); Connection Conn=NULL; PreparedStatement PS=NULL; ResultSet RS=NULL; Try{conn=jdbcutils.getconnection (); PS=conn.preparestatement (SQL);  for(inti = 0; i < args.length; i++) {Ps.setobject (i+ 1, Args[i]); } RS=Ps.executequery (); /*** Convert the resulting resultset result set to map<string, object> list, * where the key value is the alias of the RS table, the value value is the corresponding alias /c4>*/List<map<string, object>> data =Handleresultsettomaplist (RS); /*** Convert maplist to corresponding beanlist*/List=transfermaplisttobeanlist (clazz, data); }Catch(Exception e) {e.printstacktrace (); }finally{jdbcutils.release (conn, PS, RS); }        returnlist; }    Private<T> list<t> transfermaplisttobeanlist (class<t> clazz,list<map<string, Object>> data)throwsException {List<T> list =NewArraylist<>(); if(Data.size () > 0){             for(Map<string, object>map:data) {T entity=clazz.newinstance ();  for(Map.entry<string, object>Entry:map.entrySet ()) {String FieldName=Entry.getkey (); Object value=Entry.getvalue ();                Beanutils.setproperty (Entity, fieldName, value);;            } list.add (entity); }        }        returnlist; }     Public Static<E>e getforvalue (String sql, Object ... args) {e entity=NULL; Connection Conn=NULL; PreparedStatement PS=NULL; ResultSet RS=NULL; Try{conn=jdbcutils.getconnection (); PS=conn.preparestatement (SQL);  for(inti = 0; i < args.length; i++) {Ps.setobject (i+ 1, Args[i]); } RS=Ps.executequery (); if(Rs.next ()) {return(E) Rs.getobject (1); }                    }Catch(Exception e) {e.printstacktrace (); }finally{jdbcutils.release (conn, PS, RS); }        returnentity; }        /*** Process The obtained result set into Maplist *@paramRS *@return     * @throwsException*/    PrivateList<map<string, object>>handleresultsettomaplist (ResultSet rs)throwsException {List<String> Columnlabels =Getcolumnlabels (RS); List<map<string, object>> data =NewArraylist<map<string, object>>();  while(Rs.next ()) {Map<string, object> map =NewHashmap<string, object>();  for(String columnlabel:columnlabels) {Object Columnvalue=Rs.getobject (ColumnLabel);            Map.put (ColumnLabel, Columnvalue);        } data.add (map); }        returndata; }            /*** Get aliases for all columns based on the result set *@paramRS *@return     * @throwsException*/    PrivateList<string> Getcolumnlabels (ResultSet rs)throwsexception{List<String> list =NewArraylist<>(); ResultSetMetaData RSMD=Rs.getmetadata ();  for(inti = 0; I < Rsmd.getcolumncount (); i++) {List.add (Rsmd.getcolumnlabel (i+ 1)); }        returnlist; }}

Jdbc--dao design mode