分布式数据库客户端数据集的选用

<script type="text/javascript"> google_ad_client = "pub-8800625213955058"; /* 336x280, 创建于 07-11-21 */ google_ad_slot = "0989131976"; google_ad_width = 336; google_ad_height = 280; // </script> <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script> 有两种方法： 1、用vector: > public Enumeration ejbFindBigAccounts(double balanceGreaterThan) { > log("ejbFindBigAccounts (balance > " balanceGreaterThan ")"); > Connection con = null; > PreparedStatement ps = null; > > try { > con = getConnection(); > ps = con.prepareStatement("select id from ejbAccounts where bal > ?"); > ps.setDouble(1, balanceGreaterThan); > ps.executeQuery(); > ResultSet rs = ps.getResultSet(); > Vector v = new Vector(); > String pk; > while (rs.next()) { > pk = rs.getString(1); > v.addElement(pk); > } > return v.elements(); > } catch (SQLException sqe) { > log("SQLException: " sqe); > throw new EJBException (sqe); > } finally { > cleanup(con, ps); > } > } 结论：不爽，不方便。 2、RowSet RowSet tutorial chapter ： http://developer.java.sun.com/developer/Books/JDBCTutorial/chapter5.html rowset是个interface，需要有东西去实现它，sun的规范中给了三个class：cachedrowset,jdbcrowset,webrowset， 如果去查jdk1.4 doc和j2skee1.2，有rowset，却没有那三个class，一般的开发工具（至少我的wsad）中也是这样， 所以需要下jdbc2.0 opt－pack: http://developer.java.sun.com/developer/earlyAccess/crs/ 下下来了再怎么办呢？ 装呗！ 怎么装呢? setup呀！ 没有呀？ 啊，没setup呀，sun干什么吃的，连setup都不做个，也太懒了吧。 ／／／／／／／／／／／／／／／／／／／／／／／／／／／／／／／／／ 哎，我们确实是都被ms惯坏了，看到只有jar，没setup就没辙了，大家好好想想，java最大的特性是什么，就是它的类库 可以自由扩充呀，现在明白该怎么做了吧： 1、解包，得到rowset.jar，放在哪随您的意，别丢了就行。 2、在您的开发工具中增加一个路径，如：ROWSET_PATH对应：d:/jdk1.4/jre/rowset.jar（和1的路径对应就行）。 3、右键您的工程文件，出现：property（大多数工具应该都有吧），加上rowset_path。 4、在您的源文件中：import sun.jdbc.rowset.*; OK,搞定！下面就看您的了。(当然也可以把rowset压到jre里去） 应该说rowset（其实主要是CachedRowSet）真的是个好东西，和ms ado的resultset和borland的tclientset非常相似， 最大的好处是Cache功能！ 好了，看例子吧： ／／／／／／／／／／／／／server端／／／／／／／／／／／／／ package example4; import java.sql.*; import javax.sql.*; import sun.jdbc.rowset.*; import javax.naming.*; import javax.ejb.*; public class CoffeesBean implements SessionBean { private SessionContext sc = null; private Context ctx = null; private DataSource ds = null; public CoffeesBean () {} public void ejbCreate() throws CreateException { try { ctx = new InitialContext(); ds = (DataSource)ctx.lookup("jdbc/CoffeesDB"); } catch (Exception e) { System.out.println(e.getMessage()); throw new CreateException(); } } public RowSet getCoffees() throws SQLException { Connection con = null; ResultSet rs; CachedRowSet crs; try { con = ds.getConnection("webCustomer", "webPassword"); Statement stmt = con.createStatement(); rs = stmt.executeQuery("select * from coffees"); crs = new CachedRowSet(); crs.populate(rs); // the writer needs this because JDBC drivers // don't provide this meta-data. crs.setTableName("coffees"); rs.close(); stmt.close(); } finally { if (con != null) con.close(); } return rset; } public updateCoffees(RowSet rs) throws SQLException { Connection con = null; try { CachedRowSet crs = (CachedRowSet)rs; con = ds.getConnection("webCustomer", "webPassword"); moves the changes back to the database crs.acceptChanges(con); } finally { if (con != null) con.close(); } } // // Methods inherited from SessionBean // public void setSessionContext(SessionContext sc) { this.sc = sc; } public void ejbRemove() {} public void ejbPassivate() {} public void ejbActivate() {} } ／／／／／／／／／／／／／／／／／／client端／／／／／／／／／／／／／／ package example4; import java.sql.*; import javax.sql.*; import sun.jdbc.rowset.*; import javax.naming.*; import javax.ejb.*; import javax.rmi.*; class CoffeesClient { public static void main(String[] args) { try { // init the bean Context ctx = new InitialContext(); Object obj = ctx.lookup("ejb/Coffees"); CoffeesHome coffeesHome = (CoffeesHome) PortableRemoteObject.narrow(obj, CoffeesHome.class); Coffees coffees = coffeesHome.create(); // get the rowset from the bean CachedRowSet rset = (CachedRowSet)coffees.getCoffees(); // find the Columbian coffee while (rset.next()) { String coffeeName = rset.getString("COF_NAME"); if (coffeeName.equalsIgnoreCase(new String("Columbian"))) { // columbian coffee has gone up 10% rset.updateFloat("PRICE", (float)(rset.getFloat("PRICE") * 1.10)); rset.updateRow(); } } // finally send the updated back to the bean... System.out.println("Calling update method"); coffees.updateCoffees((RowSet)rset); } catch (Exception e) { System.out.println(e.getMessage()); } } } 例子很简单就不多讲了。