WSO2 ESB properties tutorial

WSO2 ESB provides properties as a way to control different aspects of the messages flowing through the mediation engine. They will not change the content (payload) of the message but they will be used to change the behavior of the message flowing through the ESB. Property mediator is used to access or modify the properties defined in the WSO2 ESB.

https://docs.wso2.org/display/ESB481/Property+Mediator

You can define a property mediator inside the ESB configuration language as below if you are setting a static value for the property.

<property name="TestProperty" value="Chanaka" scope="default" type="STRING">

If you are setting a dynamic value for the property, then you can use the following method.

<property name="TestProperty" expression="//m0:getQuote/m0:request/m0:symbol"

    xmlns:m0="http://services.samples/xsd"  scope="default" type="STRING">

In the above property declaration, you can find that we are defining a scope for the property. This scope definition will define the scope where this property can be visible inside the ESB.

1. default - or the Synapse

Once you set a property under this scope - the value of it will be available throughout both the in/out sequences.

2. axis2

Once you set a property under this scope - the value of it will be available only throughout the sequence it's been set. If you set the Property mediator to the in-sequence, you cannot access it in the out-sequence.

3. axis2-client

This is similar to Synapse scope. The difference is - you can access it in following two ways inside a custom mediator.

public boolean mediate(org.apache.synapse.MessageContext mc) {

org.apache.axis2.context.MessageContext axis2MsgContext;

axis2MsgContext = ((Axis2MessageContext) mc).getAxis2MessageContext();

String propValue = (String) axis2MsgContext.getProperty("PropName");

System.out.println("SCOPE_AXIS2_CLIENT - 1 : " + propValue);

propValue = (String) axis2MsgContext.getOptions().getProperty("PropName");

System.out.println("SCOPE_AXIS2_CLIENT - 2: " + propValue);

return true;

}

4. transport

Once you set a property under this scope - it will be added to the transport header of the out going message from the ESB.

Now we know how to define properties at different scopes. Let's see what are the properties available in the WSO2 ESB. You can find a good reference about properties from the link below.

https://docs.wso2.org/display/ESB481/Generic+Properties

In the above reference, you can find a descriptive information about most of the properties. Here is an example of using the "messageType" property.

messageType

Name	messageType
Possible Values	string
Default Behavior	Content type of incoming request.
Scope	axis2
Description	Message formatter is selected based on this property. This property should have the content type, such as text/xml, application/xml, or application/json.
Example	<property name="messageType" value="text/xml" scope="axis2"/>

Let's say you have need convert the Content-Type of your message from application/xml to application/json. Then you can use this property to achieve the same as below.

<?xml version="1.0" encoding="UTF-8"?>
<proxy xmlns="http://ws.apache.org/ns/synapse"
       name="ToJSON"
       transports="https,http"
       statistics="disable"
       trace="disable"
       startOnLoad="true">
   <target>
      <inSequence>
         <property name="messageType" value="application/json" scope="axis2"/>
         <respond/>
      </inSequence>
   </target>
   <description/>
</proxy>


To test this property, send a request to this proxy service like below.

curl -v -X POST -H "Content-Type:application/xml" -d@request1.xml "http://localhost:8280/services/tojson"

where your request1.xml is like below.

<coordinates>
   <location>
       <name>Bermuda Triangle</name>
       <n>25.0000</n>
       <w>71.0000</w>
   </location>
   <location>
       <name>Eiffel Tower</name>
       <n>48.8582</n>
       <e>2.2945</e>
   </location>
</coordinates>

You can get the response from the proxy service as below.

{"coordinates":{"location":[{"name":"Bermuda Triangle","n":25.0000,"w":71.0000},{"name":"Eiffel Tower","n":48.8582,"e":2.2945}]}}

Here you can see that the Content-Type of the message is converted to application/json.