Implementing PdxSerializable in Your Domain Object

This topic explains how to implement PdxSerializable in your domain object in VMware Tanzu GemFire.

For a domain object with source that you can modify, implement the PdxSerializable interface in the object and use its methods to serialize and deserialize the object’s fields.

Procedure

In your domain class, implement PdxSerializable, importing the required org.apache.geode.pdx classes.

For example:

import org.apache.geode.pdx.PdxReader;
import org.apache.geode.pdx.PdxSerializable;
import org.apache.geode.pdx.PdxWriter;

public class PortfolioPdx implements PdxSerializable {
  ...

If your domain class does not have a zero-arg constructor, create one for it.

For example:
```
public PortfolioPdx(){}
```
Program PdxSerializable.toData.
1. Write each standard Java data field of your domain class using the PdxWriter write methods. Tanzu GemFire automatically provides PdxWriter to the toData method for PdxSerializable objects.
2. Call the PdxWriter markIdentifyField method for each field you want to have Tanzu GemFire use to identify your object. Put this after the field’s write method. Tanzu GemFire uses this information to compare objects for operations like distinct queries. If you do not set as least one identity field, then the equals and hashCode methods will use all PDX fields to compare objects and consequently, will not perform as well. It is important that the fields used by your equals and hashCode implementations are the same fields that you mark as identity fields.
3. For a particular version of your class, you need to consistently write the same named field each time. The field names or number of fields must not change from one instance to another for the same class version.
4. For best performance, do fixed width fields first and then variable length fields.
  
  Example toData code:
```
// PortfolioPdx fields
  private int id;
  private String pkid;
  private Map<String, PositionPdx> positions;
  private String type;
  private String status;
  private String[] names;
  private byte[] newVal;
  private Date creationDate;
  ...

  public void toData(PdxWriter writer)
  {
    writer.writeInt("id", id)
    // The markIdentifyField call for a field must 
    // come after the field's write method 
    .markIdentityField("id")
    .writeDate("creationDate", creationDate) //fixed length field
    .writeString("pkid", pkid)
    .writeObject("positions", positions)
    .writeString("type", type)
    .writeString("status", status)
    .writeStringArray("names", names)
    .writeByteArray("newVal", newVal)
  }
```

Program PdxSerializable.fromData to read your data fields from the serialized form into the object’s fields using the PdxReader read methods.

Provide the same names that you did in toData and call the read operations in the same order as you called the write operations in your toData implementation.

Tanzu GemFire automatically provides PdxReader to the fromData method for PdxSerializable objects.

Example fromData code:


public void fromData(PdxReader reader)
  {
    id = reader.readInt("id");
    creationDate = reader.readDate("creationDate");
    pkid = reader.readString("pkid");
    position1 = (PositionPdx)reader.readObject("position1");
    position2 = (PositionPdx)reader.readObject("position2");
    positions = (Map<String, PositionPdx>)reader.readObject("positions");
    type = reader.readString("type");
    status = reader.readString("status");
    names = reader.readStringArray("names");
    newVal = reader.readByteArray("newVal");
    arrayNull = reader.readByteArray("arrayNull");
    arrayZeroSize = reader.readByteArray("arrayZeroSize");
  }

What to do next

As needed, configure and program your Tanzu GemFire applications to use PdxInstance for selective object deserialization. See Programming Your Application to Use PdxInstances.