Creating custom composite definition in SBE template

Each custom composite must be defined in the SBE XML template.

<composite name="NewType" description="New non-standard custom type.">
    <type name="Number" type="int32" presense="optional"/>
</composite>

Defining custom interface

@SbeCompositeType("NewType")
public interface CustomComposite {
    @SbeCompositeField("Number")
    void setN1(int value);
    @SbeCompositeField("Number")
    int getN1();
    @SbeCompositeField("Number")
    void setNullNumber();
    @SbeCompositeField("Number")
    boolean isNullNumber();
}

Getting instance of the custom composite type

Instance of the custom composite can be obtained from the ByteDecoder object:

Error during retrieving content skip as ignoreDownloadError activated.

Please pay attention that the class passed to this method must be passed to the decoder constructor when the decoder is created.

Read and write field of the custom composite type

The composite type object can be applied to read the message field or to update its value:

// The custom2Obj gets content of the composite field
msg1.getCustomComposite(9001, customObj);

customObj.setN1(12345);
msg1.getCustomComposite(9001, customObj);

Creating custom composite definition in SBE template

<composite name="NewType" description="New non-standard custom type.">
    <type name="Number" type="int32" presense="optional"/>
</composite>

Defining custom interface

@SbeCompositeType("NewType")
public interface CustomComposite {
    @SbeCompositeField("Number")
    void setN1(int value);
    @SbeCompositeField("Number")
    int getN1();
    @SbeCompositeField("Number")
    void setNullNumber();
    @SbeCompositeField("Number")
    boolean isNullNumber();
}

Getting stateless composite data instance and access fields

The stateless composite instance can be created only when there is a message or group instantiated.

CustomComposite customObject = msg1.getStatelessComposite(9001, CustomComposite.class);

The obtained object is a direct interface to low-level data and can be used to read or write such data:

Error during retrieving content skip as ignoreDownloadError activated.

Access field via its virtual ID sample

SBE template of the composite type:

<composite name="Composite2" description="Custom composite type.">
    <type name="CountOfSomething" type="int32"/>
    <type name="SizeOfSomething" type="int64"/>
</composite>

SBE template of message:

<sbe:message name="CustomMessage" id="1" description="The message with custom composite field.">
    <!-- The 35'th field required for FIX messages -->
    <field name="messageType" type="NoMatter" id="35" presence="constant" value="NoMatter.Also"/>
    <!-- The custom composite field -->
    <field name="cust1" type="Composite2" id="9001"/>
</sbe:message>

Now we need to access composite member “SizeOfSomething” of the field “cust1” in the message “CustomMessage”. To accomplish this task we need to compose the path to the field and retrieve its virtual ID.

The requested path consists of the following components:

• Message name (or ID);
• Field name (or ID);
• Composite field name.

In the case the path will be:

String[] fieldPath = new String[] {
        "CustomMessage", // Message name
        "cust1", // Field name
        "SizeOfSomething" // Composite field (element) name.
};

This path must be used for queryVirtualFieldId call after parsing of the SBE template to obtain the virtual field ID:

        Document xmlSchema = ParseUtil.parse(new File("MessageSchema.xml"));
        MessageSchema schema = new MessageSchema(xmlSchema);

        int virtualFieldId = schema.queryVirtualFieldId(fieldPath);

To successfully create the ByteDecoder it is needed to suppress custom composite recognition using empty classes.

Let's declare the empty class:

@SbeAutoRecognize
public class Composite2 {
}

…and create the decoder:

        Class<?>[] customComposites = {
                Composite2.class
        };

        ByteDecoder decoder = new ByteDecoderFactory().create(schema, customComposites);

Now we can access field using the virtual identifier:

        byte[] data = new byte[SIZE_ENOUGH_TO_ENCODE];
        IMessage msg = decoder.encode(data, 0, data.length, 1);

        // Set the virtual field value
        msg.setLong(virtualFieldId, 123L);

        // Get the virtual field value
        long v = msg.getLong(virtualFieldId);

Access message header field via its virtual field ID

Usually, there is no need to access message header fields directly: the ByteDecoder automatically updates all required information during the encoding process. But in some cases, the message header has non-standard fields. The user code must update such fields separately. The “virtual field” mechanics significantly help in the task.

Let's take the sample of non-standard message header:

<composite name="messageHeader" description="Message header with non-standard field.">
    <type name="blockLength" primitiveType="uint16"/>
    <type name="templateId" primitiveType="uint16"/>
    <type name="schemaId" primitiveType="uint16"/>
    <type name="version" primitiveType="uint16"/>
    <type name="SequenceNo" primitiveType="int32"/>
</composite>

Here, the messageHeader composite definition has a non-standard field SequenceNo. The user code must update the field explicitly.

Please note that even if the message header contains non-standard fields, there is no need to define a “custom composite” class for the header.

ByteDecoder decoder = new ByteDecoderFactory().create(schema);

This code shows how to obtain the virtual ID of the “SequenceNo” message header field. Please pay attention how the field name is declared:

        String[] headerSequenceNoFieldPath = new String[] {
                // Message header composite pseudo-name
                SpecialFieldIds.MESSAGE_HEADER_FIELD_NAME,
                
                // The message header field name
                "SequenceNo"
        };

        // Get virtual ID of the 'SequenceNo' message header field
        int seqNumID = schema.queryVirtualFieldId(headerSequenceNoFieldPath);

This message creating is trivial:

byte[] data1 = new byte[SIZE_ENOUGH_TO_ENCODE];
IMessage msg1 = decoder.encode(data, 0, data.length, 1);

And finally, the following code shows how to access SequenceNo field of the message header in the given message:

// Set the 'SequenceNo' message header field
msg1.setInt(seqNumID, 12345);
// Get the 'SequenceNo' message header field
int seqNum1 = msg1.getInt(seqNumID);