关于EJB返回值的实用解决方案
【IT168 技术文档】
1、用vector：
/**
* Finds all EJBeans with a balance greater than a given amount.
* Returns an Enumeration of found EJBean primary keys.
* @param balanceGreaterThan double Test Amount
* @return Enumeration EJBean Primary Keys
* @exception javax.ejb.EJBException
* if there is a communications or systems failure
*/
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
return v.elements();
} catch (SQLException sqe) {
log("SQLException: " + sqe);
throw new EJBException (sqe);
} finally {
cleanup(con, ps);
}
}
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/
下面：
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:jdk1.4jre owset.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！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
}
// 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。
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