Is there a way to pass a target server as a property to a java callout?

Google Cloud Apigee
1

I want to be able to pass a target server host and port as properties to a java callout policy. Is there a way to accomplish this?

I’m thinking some usage like:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<JavaCallout async="false" continueOnError="false" enabled="true" name="Java-Callout-1">
    <DisplayName>Java Callout-1</DisplayName>
    <Properties>
        <Property name="host" ref="target_server_host"/>
    </Properties>
    <ClassName>com.myorg.callouts.MyCallout</ClassName>
    <ResourceURL>java://my-callouts.jar</ResourceURL>
</JavaCallout>
1 Like
2

Yes.. Any property you pass under will be accessible inside your Java class.

public class Callout implements Execution{
   public Callout(Map<String, String> properties){
      //Map containing Host and Port properties configured in the policy.
   }
  ...
}

It’s documented here under Samples > Retrieve Property value from Java.

3

yes, you can do it, by implementing in your callout the constructor that accepts a Map<String,String> , as Sudhee stated.

But to reference a variable you cannot use the “ref” attribute. There’s no way, in the Java code, to retrieve the attributes present on a Property object. All you get is the string itself. The convention I have adopted is to wrap the value in curly-braces if it is intended to be a variable. And then at runtime, strip the braces and de-reference the variable if appropriate.

You can see a working callout that uses this approach in Edit-Xml-Node. For example, this policy config:

<JavaCallout name='Java-ReplaceXmlNode-1'>
  <Properties>
    <Property name='new-node-type'>text</Property>
    <Property name='new-node-text'>{request.queryparam.texttoinsert}</Property>
    <Property name='xpath'>{request.queryparam.xpath}</Property>
    <Property name='action'>replace</Property>
    <Property name='output-variable'>my_variable</Property>
  </Properties>
  <ClassName>com.dinochiesa.edgecallouts.EditXmlNode</ClassName>
  <ResourceURL>java://edge-custom-edit-xml-node.jar</ResourceURL>
</JavaCallout>

…tells the callout to get the value for “new-node-text” by de-referencing a queryparam called “texttoinsert”.

In the Java code, resolving a reference looks like this:

    private static final String variableReferencePatternString = "(.*?)\\{([^\\{\\} ]+?)\\}(.*?)";
    private static final Pattern variableReferencePattern = Pattern.compile(variableReferencePatternString);

    // If the value of a property contains a pair of curlies,
    // eg, {apiproxy.name}, then "resolve" the value by de-referencing
    // the context variable whose name appears between the curlies.
    private String resolvePropertyValue(String spec, MessageContext msgCtxt) {
        Matcher matcher = variableReferencePattern.matcher(spec);
        StringBuffer sb = new StringBuffer();
        while (matcher.find()) {
            matcher.appendReplacement(sb, "");
            sb.append(matcher.group(1));
            sb.append((String) msgCtxt.getVariable(matcher.group(2)));
            sb.append(matcher.group(3));
        }
        matcher.appendTail(sb);
        return sb.toString();
    }

It returns an empty string if the variable is not known.

4

I might not have formulated well my question. But what I really want to do is to access an environment target server by its name and maybe pass it to my Java callout as a property (if I cannot access out directly from the Java callout itself)

5

Thanks for the response. I might not have formulated well my question. But what I really want to do is to access an environment target server by its name and maybe pass it to my Java callout as a property (if I cannot access it directly from the Java callout itself)

6

Thanks for the response. I might not have formulated well my question. But what I really want to do is to access an environment target server by its name and maybe pass it to my Java callout as a property (if I cannot access it directly from the Java callout itself)

7

Within the Java callout policy you can get your variables directly off the context for instance for e.g.

//target.host, target.ip, target.port etc.
messageContext.getVariable("target.url");

Full list of variables can be found here. I also recommend you read the best practices before investing a lot of time on Java Callout policy. They are discussed here.