Accessing various information of a message in a mediation flow in WSO2ESB

Property mediator helps us to access various information of a message ,which passes through ESB. Within a sequence , we could use property mediator to get info about a message.
We can assign a value to a property as a string value or using xpath expression. Two actions are defined for property mediator.

• Set
• Remove

eg:

 <property name="MESSAGE" value="Executing in sequence"/>
 <property xmlns:m="http://sample.com"   name="test"   expression="//m:getQuote/m:symbol"
                   scope="default"  type="STRING"/>

We can use supported xpath functions,such as mathematical/logical operations and other predefined functions can be used to assign values in the property mediator.

eg: 

<property xmlns:ns="http://org.apache.synapse/xsd"   name="testProp"
                expression="fn:concat('hello','world')"   scope="default"/>

We can use  built in get-property() xpath function to read properties,which are available in the synapse messagecontext.
Eg: If a property "SYSTEM_TIME" available in the synapse message context; 

<property xmlns:ns="http://org.apache.synapse/xsd"   name="systemtime"
                expression="get-property('SYATEM_TIME')"   scope="default"/>

We can use property mediator to set values in different scopes, which can be accessed in those specific scope. There are 4 scopes,which are;

• synapse/default : This property will be available in both insequence and outsequence.
• axis2 : This property will be available in the particular sequence. can be retrieved from Axsi2Messagecontext.
• transport:  This scope is used to set a property in the transport header.
• axis2-client: Like "axis2" scope, but can be  retrieved form the Axis2Messagecontext.options.

eg:

<property name="myProp" value="abc" scope="default" type="STRING"/>
<property name="myProp" value="abc" scope="transport" type="STRING"/>
<property name="myProp" value="abc" scope="axis2" type="STRING"/> 
<property name="myProp" value="abc" scope="axis2-client" type="STRING"/>

When we retrieve properties from a specific scope;
eg:

 <property xmlns:ns="http://org.apache.synapse/xsd"    name="remotehost"
                    expression="get-property('axis2', 'REMOTE_HOST')"/>

There are some predefined xpath properties , which we can use directly to retrieve some common properties.

• $axis2: Used to get the property at the axis2 scope.

 eg :
 <property name="MessageType is" expression="$axis2:messageType"/>

• $trp: Used to get transport header properties.

eg:
 <property name="axis2Prop" expression="$trp:Content-Type"/>

• $ctx : Used to get synapse scope properties;

eg:
 If we have a property named as "myProp" in synapse scope, which can be retrieved in the following manner;
 <property name="testProp" expression="$ctx:myProp"/>

• $url : Used to retrieve parameters defined in the url

  eg:
For a request url; http:// localhost:8280/getSimpleQuote?symbol=IBM

<property name="symbol" expression="$url:symbol"/>
The above will retrieve the symbol value; ie:IBM

Accessing registry resources from class mediator in wso2esb

In the mediation process, users might need to access the registry resources, which are stored in the governance/config registries in wso2esb.
In the normal sequence flow, we could point the resources as registry keys in the mediators. But if we want to access them in a class mediator, where we may need to do custom process on the resource, we could retrieve the "WSO2Registry" instance from the  "SynapseConfiguration" and from the registry instance we could access different resources which are stored in the different registries.

Likewise if we have a 'LocalEntry' defined in the synapse configuration we could retrieve it from the "LocalRegistry". LocalEntries  are elements, used to declare registry entries that are local to the ESB instance. They are static resources and has high priority than a resource with the same name  hosted in embedded wso2registry.

Here is a sample class mediator, which can be used to retrieve a LocalEntry and resources hosted in governance/config registry.

import org.apache.synapse.MessageContext;
import org.apache.synapse.config.Entry;
import org.apache.synapse.mediators.AbstractMediator;
import org.apache.synapse.registry.Registry;

public class CustomRegistryRetriveMediator extends AbstractMediator {
   
    public boolean mediate(MessageContext synapseMsgContext) {

        // if localentry "testLocalentry" defined in synapse econfig
        Entry localEntryObj = (Entry) synapseMsgContext.getConfiguration()
                .getLocalRegistry().get("testLocalentry");
        System.out.println(" value: " + localEntryObj.getValue());
        System.out.println(" Filename : " + localEntryObj.getFileName());

        // goverance/config registry
        Registry regInstance = synapseMsgContext.getConfiguration()
                .getRegistry();                       
        Object obj=regInstance.getResource(new Entry("gov:/test1.txt"),null);       
        Object obj2=regInstance.getResource(new Entry("conf:/test2.txt"),null);   
       
        return true;
    }
}