Using JSON web services is easy: you send a request that defines a service method and parameters, and you receive the result as a JSON object. As easy as this technique is, it can be improved. In this tutorial, we introduce a tool that lets you use JSON web services more efficiently and pragmatically.

Consider the following example. You’re working with two related objects: a User and its corresponding Contact. With simple JSON web service calls, you first call the user service to get the user object and then you call the contact service using the contact ID from the user object. You end up sending two HTTP requests to get two JSON objects that aren’t even bound together. There’s no contact information in the user object (i.e. no user.contact). This approach is suboptimal with respect to performance (sending two HTTP calls) and usability (manually managing the relationship between two objects). It’d be nicer if you had a tool to address these inefficiencies. Fortunately, the JSON Web Service Invoker does just that!

Liferay’s JSON Web Service Invoker helps you optimize your use of JSON Web Services. In the following sections, we’ll show you how.

Simple Invoker Calls

The Invoker is accessible from the following fixed address:

http://[address]:[port]/api/jsonws/invoke

It only accepts a cmd request parameter–this is the Invoker’s command. If the command request parameter is missing, the request body is used as the command. So you can specify the command by either using the request parameter cmd or the request body.

The Invoker command is a plain JSON map that describes how JSON web services are called and how the results are managed. Here’s an example of how to call a simple service using the Invoker:

{
    "/user/get-user-by-id": {
        "userId": 123,
        "param1": null
    }
}

The service call is defined as a JSON map. The key specifies the service URL (i.e. the service method to be invoked) and the key’s value specifies a map of service parameter names (i.e. userId and param1) and their values. In the example above, the retrieved user is returned as a JSON object. Since the command is a JSON string, null values can be specified either by explicitly using the null keyword or by placing a dash before the parameter name and leaving the value empty (e.g. "-param1": '').

The example Invoker calls functions exactly the same way as the following standard JSON Web Service call:

/user/get-user-by-id?userId=123&-param1

Next, suppose that you’re running Liferay locally on port 8080. Consider the following example of a real Liferay JSON web service invoker call. Suppose that you’re signed in to Liferay as the default admin user whose email address is [email protected] and whose user ID is 20127. And suppose that the value of your p_auth authentication token is htXjvt5d. Then you can invoke the following URL to obtain a JSON representation of your user object:

http://localhost:8080/api/jsonws/invoke?cmd={%22/user/get-user-by-id%22:{%22userId%22:20172}}&p_auth=htXjvt5d

This URL uses the following JSON map. Notice that you supplied it by using the cmd URL parameter:

{
    "/user/get-user-by-id": {
        "userId": 20172
    }
}

Notice in the URL that the double quotes are URL-encoded. If you’re not sure what your user ID is, use the Dockbar to navigate to My Account. Your user ID is on the Details page. If you’re not sure what the value of your p_auth authentication token is, navigate to Liferay’s JSON web services API page and click on any method in the list. The value of your p_auth token appears under the Execute heading along with any other parameters of the selected API method.

You can use JSON syntax for supplying values for objects and arrays that you need to supply as parameters. To supply a value for an object, use curly brackets: { and }. To supply a value for an array, use square brackets: [ and ]. Suppose as before that you’re signed in to Liferay as an admin user and that the value of your p_auth authentication token is htXjvt5d. Furthermore, suppose that two vocabularies have been created with vocabulary IDs of 20783 and 20784. Here’s a real Liferay JSON web service invoker example that demonstrates how to pass an array as a parameter:

http://localhost:8080/api/jsonws/invoke?cmd={%22/assetvocabulary/get-vocabularies%22:{%22vocabularyIds%22:[20783,20784]}}&p_auth=htXjvt5d

This URL uses the following JSON map:

{
    "/assetvocabulary/get-vocabularies": {
        "vocabularyIds": [20783,20784]
    }
}

As before, the double quotes in the URL are URL-encoded. Also, the vocabularyIds parameter is an array, so its value is supplied as a JSON array.

Finally, here’s one more Liferay JSON web service invoker example that demonstrates how to pass an object containing an array as a parameter:

http://localhost:8080/api/jsonws/invoke?cmd={%22/user/add-user%22:{%22companyId%22:20127,%22autoPassword%22:false,%22password1%22:%22test%22,%22password2%22:%22test%22,%22autoScreenName%22:false,%22screenName%22:%22joe.bloggs%22,%22emailAddress%22:%[email protected]%22,%22facebookId%22:0,%22openId%22:%22%22,%22locale%22:%22en_US%22,%22firstName%22:%22Joe%22,%22middleName%22:%22T%22,%22lastName%22:%22Bloggs%22,%22prefixId%22:0,%22suffixId%22:0,%22male%22:true,%22birthdayMonth%22:1,%22birthdayDay%22:1,%22birthdayYear%22:1970,%22jobTitle%22:%22Tester%22,%22groupIds%22:null,%22organizationIds%22:null,%22roleIds%22:null,%22userGroupIds%22:null,%22sendEmail%22:false,%22serviceContext%22:{%22assetTagNames%22:[%22test%22]}}}&p_auth=htXjvt5d

This URL uses the following JSON map:

{
    "/user/add-user": {
        "companyId": 20127,
        "autoPassword": false,
        "password1": "test",
        "password2": "test",
        "autoScreenName": false,
        "screenName": "joe.bloggs",
        "emailAddress": "[email protected]",
        "facebookId": 0,
        "openId": "",
        "locale": "en_US",
        "firstName": "Joe",
        "middleName": "T",
        "lastName": "Bloggs",
        "prefixId": 0,
        "suffixId": 0,
        "male": true,
        "birthdayMonth": 1,
        "birthdayDay": 1,
        "birthdayYear": 1970,
        "jobTitle": "Tester",
        "groupIds": null,
        "organizationIds": null,
        "roleIds": null,
        "userGroupIds": null,
        "sendEmail": false,
        "serviceContext": {"assetTagNames":["test"]}
    }
}

The serviceContext is the object containing an array in this example. It contains the array assetTagNames.

Of course, the JSON Web Service Invoker handles calls to plugin methods as well:

{
    "/suprasurf-portlet.surfboard/hello-world": {
        "worldName": "Mavericks"
    }
}

The code above calls the (fictitious) SupraSurf portlet’s remote service.

You can use variables to reference objects returned from service calls. Variable names must start with a dollar sign, $. In our previous example, the service call returned a user object you can assign to a variable:

{
    "$user = /user/get-user-by-id": {
        "userId": 123,
    }
}

The $user variable holds the returned user object. You can reference the user’s contact ID using the syntax $user.contactId.

Next, see how you can use nested service calls to join information from two related objects.

Nesting Service Calls

With nested service calls, you can magically bind information from related objects together in a JSON object. You can call other services within the same HTTP request and nest returned objects in a convenient way. Here’s the magic of a nested service call in action:

{
    "$user = /user/get-user-by-id": {
        "userId": 123,
        "$contact = /contact/get-contact-by-id": {
            "@contactId": "$user.contactId"
        }
    }
}

This command defines two service calls: the contact object returned from the second service call is nested in (i.e. injected into) the user object, as a property named contact. Now we can bind the user and his or her contact information together!

Let’s see what the Invoker did in the background when we used a single HTTP request to make the above nested service call:

  • First, the Invoker called the Java service mapped to /user/get-user-by-id, passing in a value for the userId parameter.
  • Next, the resulting user object was assigned to the variable $user.
  • The nested service calls were invoked.
  • The Invoker called the Java service mapped to /contact/get-contact-by-id by using the contactId parameter, with the $user.contactId value from the object $user.
  • The resulting contact object was assigned to the variable $contact.
  • Lastly, the Invoker injected the contact object referenced by $contact into the user object’s property named contact.

Next, let’s talk about filtering object properties so that only the properties you need are returned when you invoke a service.

Filtering Results

Many of Liferay Portal’s model objects are rich with properties. If you only need a handful of an object’s properties for your business logic, making a web service invocation that returns all of an object’s properties is a waste of network bandwidth. With the JSON Web Service Invoker, you can define a white-list of properties: only the specific properties you request in the object will be returned from your web service call. Here’s how you white-list the properties you need:

{
    "$user[firstName,emailAddress] = /user/get-user-by-id": {
        "userId": 123,
        "$contact = /contact/get-contact-by-id": {
            "@contactId": "$user.contactId"
        }
    }
}

In this example, the returned user object has only the firstName and emailAddress properties (it still has the contact property, too). To specify white-list properties, you simply place the properties in square brackets (e.g., [whiteList]) immediately following the name of your variable.

Let’s talk about batching calls next.

Batching Calls

When we nested service calls earlier, the intent was to invoke multiple services with a single HTTP request. Using a single request for multiple service calls is helpful for gathering related information from the service call results, but it can also be advantageous to use a single request to invoke multiple unrelated service calls. The Invoker lets you batch service calls together to improve performance. It’s simple: just pass in a JSON array of commands using the following format:

[
    {/* first command */},
    {/* second command */}
]

The result is a JSON array populated with results from each command. The commands are collectively invoked in a single HTTP request, one after another.

Now that you’ve learned the ins and outs of invoking JSON web services in Liferay, you may want to consider taking a streamlined approach to accessing Web Content articles and Dynamic Data List records. Liferay’s Skinny JSON Provider app gives you access to them and returns them in an easy-to-use fashion. For more information, please refer to the Invoking Services Using Skinny JSON Provider tutorial.

Related Topics

Registering JSON Web Services

Invoking JSON Web Services

JSON Web Services Invocation Examples

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