Components of a Web Service (Real-Time, Windows)

LabVIEW 2018 Help

Edition Date: March 2018
Part Number: 371361R-01
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Parent Topic: Overview: Web-based Communication with a LabVIEW Application

A Web service can include HTTP method VIs, HTTP method VI dependencies, startup VIs, and static content files. Organize Web service files in a LabVIEW project under a parent Web service project item.

Note  For more information about concepts in this topic, refer to the Web services introduction and tutorial. LabVIEW Web services are available only in the LabVIEW Full Development System and the LabVIEW Professional Development System.

The following project shows a Web service project item and the subitems that you use to organize and configure Web service files. To add the top-level Web service project item, right-click a target, such as My Computer, and select New»Web Service.

HTTP Method VIs

HTTP method VIs are the top-level VIs in a Web service that contain the core functionality of that Web service. When a web client sends an HTTP request to a Web service, the Web service accepts the request and routes it to a specific HTTP method VI. HTTP method VIs and web clients exchange data over a network.

Right-click the Web Resources project item and select New VI to create a new HTTP method VI.

You can add sub-items under the Web Resources project item to organize HTTP method VIs. These subfolders are useful in RESTful design for grouping HTTP method VIs that perform actions on the same resource, such as a collection of users. RESTful refers to the Representational State Transfer (REST) architecture.

The name of a subfolder also appears in the URL that clients use to invoke HTTP method VIs you place in the subfolder. For example, in the following figure, the URL for the HTTP method VI includes AdditionalOperations after the service name:

Related Information

Developing HTTP Method VIs

Sending Data to a Published Application using URLs

HTTP Method VI Dependencies

HTTP method VI dependencies are necessary components of the HTTP method VIs you develop. Dependencies can include subVIs, shared variables, DAQ channels, and other components that appear within an HTTP method VI.

LabVIEW Web services automatically package some HTTP method VI dependencies, such as subVIs, when you publish the Web service. Published Web services do not include HTTP method VI dependencies such as shared variables.

Startup VIs

Startup VIs run as part of a Web service, but unlike HTTP method VIs, they do not exchange data with web clients. You might use a startup VI to perform one or more of the following tasks in a Web service:

  • Load data from a file to initialize a value.
  • Process and manipulate data the Web service receives from clients.
  • Periodically save data to a file while the Web service runs.

A LabVIEW application that includes a Web service also can perform the previous tasks. However, for stand-alone Web services that are not part of an application, use startup VIs instead. Note that startup VIs can exchange data with HTTP method VIs without using network resources, which can increase application efficiency.

Right-click the Startup VIs project item and select New VI to create a new startup VI. Each Web service can include multiple startup VIs.

Related Information

Developing Startup VIs to Initialize and Communicate with HTTP Method VIs

Static Content

You can publish static content alongside HTTP method VIs in a Web service. Examples of static content are HTML files, stylesheets, images, movies, and JavaScripts.

Right-click the Web service and select Add Public Content Folder or Add Private Content Folder to add folders to the project and map them to folders of static content on disk. Organize static content on disk in two main folders to mirror the organization in the project tree—one main folder that contains public content and one that contains private content:

  • Private Content—Clients cannot access files in the private folder via HTTP requests. Only VIs in the Web service can use private static content. Examples of files you might want to make private are ESP scripts and configuration files. Private files do not have URL mappings.
  • Public Content—Clients can access public static content via HTTP requests. Examples of files you might want to make public are HTML pages and images. LabVIEW automatically assigns each public file a URL mapping.

The main folders can contain subfolders, such as Public Folder\html and Public Folder\images. The folders in the project tree are auto-populating by default, which means they update in real time to reflect the contents of folders on disk.

Related Information

Integrating Static Content into a Web Service

Converting a Web Service Build Specification to a Project Item

In LabVIEW 2012 and earlier, you configure Web service files in a Web service build specification rather than directly in the project tree as the previous sections in this topic describe. You can continue to use build specifications you created in LabVIEW 2012 or earlier, or you can convert them to Web service project items. To download a conversion tool, visit the National Instruments website.

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