Using a Class Mediator to process JSON payload

 

This blog post describes about using a class mediator to process  JSON payload

sample JSON:

{
   "query": "InformationSystem[@id\u003d\"22174\"]",
   "result": [
    {
      "id": [
        "22174"
      ],
      "description": [
        "test 123"
      ],
      "Application Type": [
        "Sample Application"
      ],
      "{Sample} ID": [
        "ID1"
      ]
    }
  ]
}


You can use WSO2 Developer Studio to create a mediator project and since I have used jackson as the library I have added below dependencies to the pom.xml of the mediator project

         <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.7.2</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.7.2</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.7.2</version>
        </dependency>
        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-core-asl</artifactId>
            <version>1.9.3</version>
        </dependency>
        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-mapper-asl</artifactId>
            <version>1.9.3</version>
        </dependency>
        <dependency>
            <groupId>org.apache.synapse</groupId>
            <artifactId>synapse-commons</artifactId>
            <version>2.1.2-wso2v4</version>
        </dependency>


The code is as follows:

package org.wso2.sample;

import java.util.Iterator;
import java.util.Map;

import org.apache.synapse.MessageContext;
import org.apache.synapse.commons.json.JsonUtil;
import org.apache.synapse.core.axis2.Axis2MessageContext;
import org.apache.synapse.mediators.AbstractMediator;

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.fasterxml.jackson.databind.node.TextNode;

public class JSONClassMediator extends AbstractMediator {

    public static final String RESULT_NODE = "result";
    public static final String QUERY_NODE = "query";

    @SuppressWarnings("deprecation")
    public boolean mediate(MessageContext context) {
        try {
            // Getting the json payload to a string
            String jsonPayloadToString = JsonUtil.jsonPayloadToString(((Axis2MessageContext) context)
                    .getAxis2MessageContext());

            JsonFactory factory = new JsonFactory();
            ObjectMapper mapper = new ObjectMapper(factory);

            JsonNode rootNode = mapper.readTree(jsonPayloadToString);
            //create a new root object
            ObjectNode rootObject = mapper.createObjectNode();
           
            //process query node
            TextNode queryNodeValue = (TextNode) rootNode.get(QUERY_NODE);
            rootObject.put(QUERY_NODE, queryNodeValue.asText());
           
            //process result node
            ArrayNode resultNode = (ArrayNode) rootNode.get(RESULT_NODE);
            JsonNode resultChildNode = ((ArrayNode) resultNode).get(0);
            Iterator<Map.Entry<String, JsonNode>> fieldsIterator = resultChildNode.fields();
            ObjectNode newNode = mapper.createObjectNode();
            ArrayNode resultArray = mapper.createArrayNode();
            while (fieldsIterator.hasNext()) {
                Map.Entry<String, JsonNode> field = fieldsIterator.next();
                String newKey = field.getKey().replace(" ", "-").replace("{", "").replace("}", "").replace("%", "");
                newNode.put(newKey, field.getValue());
            }          
            resultArray.add(newNode);
            rootObject.put(RESULT_NODE, (JsonNode) resultArray);
       
            // Setting the new json payload.
            String transformedJson = rootObject.toString();
            JsonUtil.newJsonPayload(((Axis2MessageContext) context).getAxis2MessageContext(), transformedJson, true,
                    true);

        } catch (Exception e) {
            handleException("error in processing the json payload", e,context);
            return false;
        }

        return true;
    }
}

Proxy configuration is as follows:

<?xml version="1.0" encoding="UTF-8"?>

<proxy xmlns="http://ws.apache.org/ns/synapse"

       name="sampleProxy"

       transports="https,http"

       statistics="disable"

       trace="disable"

       startOnLoad="true">

   <target>

      <inSequence>

         <call>

            <endpoint key="conf:/repository/sampleEP"/>

         </call>

         <class name="org.wso2.sample.JSONClassMediator"/>

         <log level="full">

            <property name="************RESULT************" expression="$body"/>

         </log>

      </inSequence>

   </target>

   <description/>

</proxy>

 

 

Result:

 

<jsonObject>
      <query>InformationSystem[@id="22174"]</query>
      <result>
         <id>22174</id>
         <description>test 123</description>
         <Application-Type>Sample Application</Application-Type>
         <Sample-ID>ID1</Sample-ID>
      </result>
  </jsonObject>