We need to produce jsp's with specific data of a EJB. If we create one VO for each screen we'd be tying my web layer into the ejb layer. If I use a generic VO we'd be wasting bandwidth (we use a expensive satelite). We create a design that asks for especific data (sending a page code and retrieved in the server using reflection and xml for setting up) that populates a hashtable and then serializes it back to the client. Have someone used this design ? If this design is strange what's the best solution.

Emerson

Hi,
I would prefer the following architecture for this problem:Create a standard VO with x properties and assign each property an index number. The VO is instantiated on both sides (both EJB and JSP layer) and uses a simple transfer class for transporting the values. This transfer class uses a byte array for storing the indexes (assuming the VO doesn't have more than 256 properties) and an object array for the values.
This design provides a nearly transparent use of a small carrier object and needs less bandwidth, as instead of objects byte values are used for indexing the needed information.
Here's a simple example to clarify things:

public class SomeBeanVO {

private Integer value; // #1
private String name; // #2
// more properties

private int count; // Counts the used properties

// Example of counting properties with setters
public void setValue(Integer v) {
if (value==null && v != null)
count++;
if (value!=null && v == null)
count--;
value=v;
}

// more getters and setter

// This method request the data from the bean
public Carrier getCarrier() {

Carrier c=new Carrier();
c.index=new byte[count];
c.values=new Object[count];

// encode properties
int place=0;
if (value != null) {
c.index[place]=new Byte(1);
c.values[place]=value;
place++;
}
if (name != null) {
c.index[place]=new Byte(1);
c.values[place]=value;
place++;
}
// add other properties if needed
return c;
}
Carrier ret = beanRemote.getData(c);

public SomeBeanVO(Carrier c)

// decode c
for (int i=0;i<c.index.length;i++) {
if (c.index[i]==1) {
value=c.values[i];
continue;
} else if (c.index[i]==2) {
name=c.values[i];
continue;
}
//...
}
count=c.index.length;
}
} // from class

public class Carrier extends Serializable{
public byte[] index;
public Object[] values;
}

The Remote Interface of the EJB uses Carriers instead of VO, but both EJB class and client can use the standard behaviour of a simple VO, which uses the carrier for creation.

Wishing you success,
Markus Zywitza

This line does not belong there:

Carrier ret = beanRemote.getData(c);

Markus Zywitza

"We need to produce jsp's with specific data of a EJB. If we create one VO for each screen we'd be tying my web layer into the ejb layer."

Your web layer is tied to the EJB layer -- it can only read/write properties which the EJB layer understands.

VOs will tell you this at compile time, HashMaps won't.

You can make both the Web layer and EJB layer depend on a set of interfaces which define the minimum set of properties a particular VO must have.

Tom