Accessing Properties with XPath¶
The WSO2 Micro Integrator supports standard XPath functions and variables through its underlying XPath engine. It supports XPath 1.0 by default where as the support for XPath 2.0 can be introduced by adding the following property in
[mediation]
synapse.enable_xpath_dom_failover=true
The Micro Integrator also provides custom XPath functions and variables for accessing message properties.
XPath Extension Functions¶
In addition to standard XPath functions, the Micro Integrator supports the following custom functions for working with XPath expressions:
base64Encode() function¶
The base64Encode function returns the base64-encoded value of the specified string.
Syntax:
base64Encode(string value)
base64Encode(string value, string charset)
base64Decode() function¶
The base64Decode function returns the original value of the specified base64-encoded value.
Syntax:
base64Decode(string encodedValue)
base64Decode(string encodedValue , string charset)
get-property() function¶
The get-property()
function allows any XPath expression used in a configuration to look up information from the current message context. Using the Property mediator, you can retrieve properties from the message context and header.
The syntax of the function takes the following format.
get-property(String propertyName)
get-property(String scope, String propertyName)
The function accepts scope as an optional parameter. It retrieves a message property at the given scope, which can be one of the following.
If you provide only the property name without the scope, the default s
ynapse
scope will be used.
Info
When the result of an XPath evaluation results in a single XML node, the evaluator will return the text content of this node by default (equivalent of doing /root/body/node/text()). If you want to retrieve the node itself, you can configure the Enrich mediator as shown in the following example.
<inSequence>
<log level="custom">
<property name="WHERE" value="before doing stuff"/>
</log>
<enrich>
<source type="body" clone="true"/>
<target type="property" property="ENRICH_PROPERTY"/>
</enrich>
<property name="PROPERTY_PROPERTY"
expression="$body/child::node()"
scope="default"/>
<log level="custom">
<property name="WHERE" value="before doing stuff"/>
<property name="ENRICH_PROPERTY" expression="get-property('ENRICH_PROPERTY')"/>
<property name="PROPERTY_PROPERTY" expression="get-property('PROPERTY_PROPERTY')"/>
</log>
<enrich>
<source type="property" clone="true" property="ENRICH_PROPERTY"/>
<target type="body" action="sibling"/>
</enrich>
<log level="full"/>
</inSequence>
Synapse scope¶
When the scope of a property mediator is synapse
,
its value is available throughout both the in sequence and the out
sequence. In addition to the user-defined properties, you can retrieve
the following special properties from the synapse
scope.
Name | Return Value |
To | Incoming URL as a String, or empty string («») if a To address is not defined. |
From | From address as a String, or empty string («») if a From address is not defined. |
Action | SOAP Addressing Action header value as a String, or empty string («») if an Action is not defined. |
FaultTo | SOAP FaultTo header value as a String, or empty string («») if a FaultTo address is not defined. |
ReplyTo | ReplyTo header value as a String, or empty string («») if a ReplyTo address is not defined. |
MessageID | A unique identifier (UUID) for the message as a String, or empty string («») if a MessageID is not defined. This ID is guaranteed to be unique. |
FAULT | TRUE if the message has a fault, or empty string if the message does not have a fault. |
MESSAGE_FORMAT | Returns pox, get, soap11, or soap12 depending on the message. If a message type is unknown this returns soap12 |
OperationName | Operation name corresponding to the message. A proxy service with a WSDL can have different operations. If the WSDL is not defined, ESB defines fixed operations. |
To access a property with the synapses
cope inside the mediate()
method of a mediator, you can include the following configuration in a custom mediator created using the Class mediator:
public boolean mediate(org.apache.synapse.MessageContext mc) {
// Available in both in-sequence and out-sequenc
String propValue = (String) mc.getProperty("PropName");
System.out.println("SCOPE_SYNAPSE : " + propValue);
return true;
}
axis2 scope¶
When the scope of a property mediator is axis2
, its
value is available only throughout the sequence for which the property
is defined (e.g., if you add the property to an in sequence, its value
will be available only throughout the in sequence). You can retrieve
message context properties within the axis2
scope
using the following syntax.
Syntax:
get-property('axis2', String propertyName)
To access a property with the axis2
scope inside the mediate()
method of a mediator, you can include the following configuration in a custom mediator created using the Class mediator:
public boolean mediate(org.apache.synapse.MessageContext mc) {
org.apache.axis2.context.MessageContext axis2MsgContext;
axis2MsgContext = ((Axis2MessageContext) mc).getAxis2MessageContext();
// Available only in the sequence the property is defined.
String propValue = (String) axis2MsgContext.getProperty("PropName");
System.out.println("SCOPE_AXIS2 : " + propValue);
return true;
}
axis2-client¶
This is similar to the synapse
scope. The difference is that it can be accessed inside the
mediate()
method of a mediator by including one of
the following configurations in a custom mediator, created using the
Class 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);
or
propValue = (String) axis2MsgContext.getOptions().getProperty("PropName");
System.out.println("SCOPE_AXIS2_CLIENT - 2: " + propValue);
return true;
}
transport scope¶
When the scope of a property mediator is transport
,
it will be added to the transport header of the outgoing message from
the ESB profile. You can retrieve message context properties within the
transport
scope using the following syntax.
Syntax:
get-property('transport', String propertyName)
registry scope¶
You can retrieve properties within the registry using the following syntax.
Syntax:
get-property('registry', String registryPath@propertyName)
get-property('registry', String registryPath)
system scope¶
You can retrieve Java System properties using the following syntax.
Syntax:
get-property('system', String propertyName)
environment scope¶
Info
The environment scope for the property mediator is available as a product update from 17th June, 2020 onwards. See the instructions on getting product updates.
You can retrieve environment variables using the following syntax.
Syntax:
get-property('env', String propertyName)
operation scope¶
You can retrieve a property in the operation context level from the
operation
scope. The properties within
iterated/cloned message with the operation
scope are
preserved in the in sequence even if you have configured your API
resources to be sent through the fault sequence when faults exist. A
given property with the operation
scope only exists
in a single request and can be accessed by a single resource. The
properties in this scope are passed to the error handler when the
FORCE_ERROR_ON_SOAP_FAULT
property is set to
true
. See FORCE_ERROR_ON_SOAP_FAULT
section in Generic Properties for more information.
Syntax:
get-property('operation', String propertyName)
url-encode() function¶
The url-encode function returns the URL-encoded value of the specified string.
Syntax:
- url-encode(string value)
- url-encode(string value, string charset)
Synapse XPath Variables¶
There is a set of predefined XPath variables that you can directly use to write XPaths in the Synapse configuration, instead of using the synapse:get-property() function . These XPath variables get properties of various scopes as follows:
$body¶
The SOAP 1.1 or 1.2 body element. For example, the expression $body//getQuote refers to the first getQuote element in a SOAP body, regardless of whether the message is SOAP-11 or SOAP-12. We have discussed an example below.
Example of $body usage:
-
Deploy the following proxy service using instructions in Creating a Proxy Service.
Note the property,
<property xmlns:m0=" http://services.samples " name="stockprop" expression="$body//m0:getQuote"/>
in the configuration. It is used to log the first<m0:getQuote>
element of the request SOAP body.<proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true"> <target> <inSequence> <log> <property xmlns:m0="http://services.samples" name="stockprop" expression="$body//m0:getQuote"/> </log> <send> <endpoint> <address uri="http://localhost:9000/services/SimpleStockQuoteService"/> </endpoint> </send> </inSequence> <outSequence> <send/> </outSequence> </target> <description></description> </proxy>
-
Send the following StockQuote request:
ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy
-
Note the following message in the log.
[2013-03-18 14:04:41,019] INFO - LogMediator To: /services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:930f68f5-199a-4eff-90d2-ea679c2362ab, Direction: request, stockprop = <m0:getQuotexmlns:m0="http://services.samples"><m0:request><m0:symbol>IBM</m0:symbol></m0:request></m0:getQuote>
$header¶
The SOAP 1.1 or 1.2 header element. For example, the expression $header/wsa:To refers to the addressing To header regardless of whether this message is SOAP-11 or SOAP-12. We have discussed an example below.
Example of $header usage :
-
Deploy the following proxy service using instructions in Creating a Proxy Service.
Note the property,
<property xmlns:wsa=" http://www.w3.org/2005/08/addressing " name="stockprop" expression="$header/wsa:To"/>
in the configuration. It is used to log the value of wsa:To header of the SOAP request.<proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true"> <target> <inSequence> <log> <property xmlns:wsa="http://www.w3.org/2005/08/addressing" name="stockprop" expression="$header/wsa:To"/> </log> <send> <endpoint> <address uri="http://localhost:9000/services/SimpleStockQuoteService"/> </endpoint> </send> </inSequence> <outSequence> <send/> </outSequence> </target> <description></description> </proxy>
-
Send the following StockQuote request:
ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy
-
Note the following message in the log.
[2013-03-18 14:14:16,356] INFO - LogMediator To: http://localhost:9000/services/SimpleStockQuoteService, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:8a64c9cb-b82f-4d6f-a45d-bef37f8b664a, Direction: request, stockprop = http://localhost:9000/services/SimpleStockQuoteService
$axis2¶
Prefix for Axis2 MessageContext properties. This is used to get the property value at the axis2 scope. For example, to get the value of Axis2 message context property with name REST_URL_POSTFIX, use the XPath expression $axis2:REST_URL_POSTFIX. We have discussed an example below.
Example of $axis2 usage :
-
Deploy the following proxy service. For instructions, see Creating a Proxy Service.
Note the property,
<property name="stockprop" expression="$axis2:REST_URL_POSTFIX"/>
in the configuration which is used to log the REST_URL_POSTFIX value of the request message.<proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true"> <target> <inSequence> <log> <property name="stockprop" expression="$axis2:REST_URL_POSTFIX"/> </log> <send> <endpoint> <address uri="http://localhost:9000/services/SimpleStockQuoteService"/> </endpoint> </send> </inSequence> <outSequence> <send/> </outSequence> </target> <description></description> </proxy>
-
Send the following StockQuote request:
ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy/test/prefix
-
Note the following message in the log.
INFO - LogMediator To: http://localhost:8280/services/StockQuoteProxy/test/prefix, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:ecd228c5-106a-4448-9c83-3b1e957e2fe5, Direction: request, stockprop = /test/prefix
In this example, the property definition,
<property name="stockprop" expression="$axis2:REST_URL_POSTFIX"/>
is equivalent to
<property name="stockprop" expression="get-property('axis2','REST_URL_POSTFIX')"/>
Similarly, you can use $axis2 prefix with HTTP Transport Properties.
$ctx¶
Prefix for Synapse MessageContext properties and gets a property at the default scope. For example, to get the value of Synapse message context property with name ERROR_MESSAGE, use the XPath expression $ctx:ERROR_MESSAGE. We have discussed an example below.
Example of $ctx usage:
This example sends a request to a sample proxy service, and sets the target endpoint to a non-existent endpoint reference key. It causes a mediation fault, which triggers the fault sequence.
-
Deploy the following proxy service. For instructions, see Creating a Proxy Service.
Note the property,
<property name="stockerrorprop" expression="$ctx:ERROR\_MESSAGE"/\>
in the fault sequence configuration. It is used to log the error message that occurs due to a mediation fault.<proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true"> <target> <inSequence> <send> <endpoint key="ep2"/> </send> </inSequence> <outSequence> <send/> </outSequence> <faultSequence> <log> <property name="stockerrorprop" expression="$ctx:ERROR_MESSAGE"/> <property name="Cause" expression="get-property('ERROR_MESSAGE')"/> </log> </faultSequence> </target> <description></description> </proxy>
-
Send the following StockQuote request:
ant stockquote -Dtrpurl=http://localhost:8280/services/StockQuoteProxy
-
Note the following message in the log.
INFO - LogMediator To: /services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:54205f7d-359b-4e82-9099-0f8e3bf9d014, Direction: request, stockerrorprop = Couldn't find the endpoint with the key : ep2
In this example, the property definition, \<property name="stockerrorprop" expression="$ctx:ERROR_MESSAGE"/> is equivalent to \<property name="stockerrorprop" expression="get-property('ERROR_MESSAGE')"/>.
Similarly, you can use $ctx prefix with Generic Properties .
$trp¶
Prefix used to get the transport headers. For example, to get the transport header named Content-Type of the current message, use the XPath expression $trp:Content-Type . HTTP transport headers are not case sensitive. Therefore, $trp:Content-Type and $trp:CONTENT-TYPE are regarded as the same. We have discussed an example below.
Example of $trp usage:
-
Deploy the following proxy service. For instructions, see Creating a Proxy Service.
Note the property, \<property name="stockprop" expression="$trp:Content-Type"/> in the configuration, which is used to log the Content-Type HTTP header of the request message.
<proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true"> <target> <inSequence> <log> <property name="stockprop" expression="$trp:Content-Type"/> </log> <send> <endpoint> <address uri="http://localhost:9000/services/SimpleStockQuoteService"/> </endpoint> </send> </inSequence> <outSequence> <send/> </outSequence> </target> <description></description> </proxy>
-
Send the following StockQuote request:
ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy
-
Note the following message in the log.
[2013-03-18 12:23:14,101] INFO - LogMediator To: http://localhost:8280/services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:25a3143a-5b18-4cbb-b8e4-27d4dd1895d2, Direction: request, stockprop = text/xml; charset=UTF-8
In this example, the property definition, \<property name="stockprop" expression="$trp:Content-Type"/> is equivalent to \<property name="stockprop" expression="get-property('transport','Content-Type')"/>. Similarly, you can use $trp prefix with HTTP Transport Properties .
$url¶
The prefix used to get the URI element of a request URL.
Example of $url usage:
-
Create a REST API with the following configuration using instructions given in page Working with APIs.
<api xmlns="http://ws.apache.org/ns/synapse" name="Editing" context="/editing"> <resource methods="GET" uri-template="/edit?a={symbol}&b={value}"> <inSequence> <log level="full"> <property name="SYMBOL" expression="$url:a"></property> <property name="VALUE" expression="$url:b"></property> </log> <respond></respond> </inSequence> </resource> </api>
-
Send a request to the REST API you created using a browser as follows:
http://10.100.5.73:8280/editing/edit?a=wso2&b=2.4
You will see the following in the log:
LogMediator To: /editing/edit?a=wso2&b=2.4, MessageID: urn:uuid:36cb5ad7-f150-490d-897a-ee7b86a9307d, Direction: request, SYMBOL = wso2, VALUE = 2.4, Envelope: <?xml version="1.0" encoding="utf-8"?><soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"><soapenv:Body></soapenv:Body></soapenv:Envelope>
$func¶
The prefix used to refer to a particular parameter value passed externally by an invoker such as the Call Template Mediator .
Example of $func usage:
-
Add a sequence template with the following configuration. See Adding a New Sequence Template for detailed instructions.
<template xmlns="http://ws.apache.org/ns/synapse" name="HelloWordLogger"> <sequence> <log level="full"> <property xmlns:ns2="http://org.apache.synapse/xsd" xmlns:ns="http://org.apache.synapse/xsd" name="message" expression="$func:message"></property> </log> </sequence> </template>
-
Deploy the following proxy service. For instructions, see Creating a Proxy Service.
<proxy xmlns="http://ws.apache.org/ns/synapse" name="StockQuoteProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true"> <target> <inSequence> <call-template target="HelloWorldLogger"> <with-param name="message" value="HelloWorld"/> </call-template> <log/> </inSequence> <outSequence> <send/> </outSequence> <endpoint> <address uri="http://localhost:9000/services/SimpleStockQuoteService"/> </endpoint> </target> <description/> </proxy>
-
Send the following StockQuote request:
ant stockquote -Daddurl=http://localhost:8280/services/StockQuoteProxy
-
Note the following message in the log.
LogMediator To: http://localhost:8280/services/StockQuoteProxy, WSAction: urn:getQuote, SOAPAction: urn:getQuote, ReplyTo: http://www.w3.org/2005/08/addressing/anonymous, MessageID: urn:uuid:8d90e21b-b5cc-4a02-98e2-24b324fa704c, Direction: request, message = HelloWorld
$env¶
Prefix used to get a SOAP 1.1 or 1.2 envelope level element. For example, to get the body element from the SOAP envelope, use the expression $env/*[local-name()='Body'] .
Example of $env usage:
-
Create an API with the following configuration. For information on how to create an API, see Working with APIs.
<api context="/soapEnvelopeTest" name="SoapEnvelopeTest"> <resource url-mapping="/*"> <inSequence> <loopback/> </inSequence> <outSequence> <property name="messageType" scope="axis2" value="application/xml"/> <payloadFactory media-type="xml"> <format> <theData xmlns="http://some.namespace"> <item>$1</item> </theData> </format> <args> <arg evaluator="xml" expression="$env/*[local-name()='Body']/*[local-name()='jsonObject']/*"/> </payloadFactory> <property name="messageType" scope="axis2" value="application/json"/> <send/> </outSequence> </resource> </api>
-
Send a post request to the API you created (i.e., http://localhost:8280/soapEnvelopeTest), with the following json payload using a rest client.
{"content":{ "paramA": "ValueA", "paramB": "valueB" }}
You will receive the following response:
{"theData":{"item":{"content":{"paramA":"ValueA","paramB":"valueB"}}}}