In this module, we will explore how COBOL can interact with web services. This is an advanced topic that bridges traditional COBOL applications with modern web technologies, enabling COBOL programs to consume and provide web services.
Key Concepts
-
Web Services Overview
- Definition and purpose of web services.
- Types of web services: SOAP and REST.
- How web services facilitate communication between different systems.
-
SOAP vs. REST
- SOAP (Simple Object Access Protocol)
- Protocol-based.
- Uses XML for message format.
- More rigid and standardized.
- REST (Representational State Transfer)
- Architectural style.
- Uses various formats (XML, JSON, etc.).
- More flexible and lightweight.
- SOAP (Simple Object Access Protocol)
-
COBOL and Web Services Integration
- How COBOL can consume web services.
- How COBOL can provide web services.
Practical Example: Consuming a Web Service in COBOL
Step 1: Understanding the Web Service
For this example, we will consume a RESTful web service that provides currency exchange rates. The service endpoint is:
This endpoint returns exchange rates for USD in JSON format.
Step 2: Setting Up the Environment
Ensure you have the necessary tools and libraries to make HTTP requests and parse JSON in COBOL. This might involve using third-party libraries or tools that support HTTP and JSON.
Step 3: Writing the COBOL Program
Here is a simplified example of a COBOL program that consumes the web service:
IDENTIFICATION DIVISION.
PROGRAM-ID. ConsumeWebService.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SPECIAL-NAMES.
CALL-CONVENTION 1 IS STDCALL.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-URL PIC X(100) VALUE 'https://api.exchangerate-api.com/v4/latest/USD'.
01 WS-RESPONSE PIC X(1000).
01 WS-STATUS-CODE PIC 9(3).
PROCEDURE DIVISION.
CALL 'HTTP-GET' USING WS-URL
WS-RESPONSE
WS-STATUS-CODE.
IF WS-STATUS-CODE = 200
DISPLAY 'Response: ' WS-RESPONSE
ELSE
DISPLAY 'Error: Unable to fetch data, status code ' WS-STATUS-CODE
END-IF.
STOP RUN.Explanation
- IDENTIFICATION DIVISION: Defines the program name.
- ENVIRONMENT DIVISION: Specifies special names and configurations.
- DATA DIVISION: Declares variables for the URL, response, and status code.
- PROCEDURE DIVISION: Contains the logic to call the web service and handle the response.
Step 4: Parsing the JSON Response
To parse the JSON response, you would typically use a JSON parsing library. Here is a conceptual example:
01 WS-JSON-RESPONSE.
05 WS-RATES.
10 WS-EUR-RATE PIC 9(5)V9(4).
PROCEDURE DIVISION.
CALL 'HTTP-GET' USING WS-URL
WS-RESPONSE
WS-STATUS-CODE.
IF WS-STATUS-CODE = 200
CALL 'PARSE-JSON' USING WS-RESPONSE
WS-JSON-RESPONSE
DISPLAY 'EUR Rate: ' WS-EUR-RATE
ELSE
DISPLAY 'Error: Unable to fetch data, status code ' WS-STATUS-CODE
END-IF.
STOP RUN.Explanation
- WS-JSON-RESPONSE: Structure to hold parsed JSON data.
- PARSE-JSON: Hypothetical subroutine to parse JSON.
Practical Exercise
Task
Write a COBOL program that consumes a RESTful web service to get weather information. Use the following endpoint:
Parse the JSON response to extract and display the current temperature in London.
Solution
IDENTIFICATION DIVISION.
PROGRAM-ID. ConsumeWeatherService.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SPECIAL-NAMES.
CALL-CONVENTION 1 IS STDCALL.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-URL PIC X(100) VALUE 'https://api.weatherapi.com/v1/current.json?key=YOUR_API_KEY&q=London'.
01 WS-RESPONSE PIC X(1000).
01 WS-STATUS-CODE PIC 9(3).
01 WS-JSON-RESPONSE.
05 WS-CURRENT.
10 WS-TEMP-C PIC 9(2)V9(1).
PROCEDURE DIVISION.
CALL 'HTTP-GET' USING WS-URL
WS-RESPONSE
WS-STATUS-CODE.
IF WS-STATUS-CODE = 200
CALL 'PARSE-JSON' USING WS-RESPONSE
WS-JSON-RESPONSE
DISPLAY 'Current Temperature in London: ' WS-TEMP-C '°C'
ELSE
DISPLAY 'Error: Unable to fetch data, status code ' WS-STATUS-CODE
END-IF.
STOP RUN.Explanation
- Replace
YOUR_API_KEYwith your actual API key. - The program fetches weather data and parses the JSON response to display the current temperature.
Common Mistakes and Tips
- Incorrect URL: Ensure the URL is correct and properly formatted.
- Handling Errors: Always check the status code and handle errors gracefully.
- Parsing JSON: Ensure the JSON structure matches your data structure in COBOL.
Conclusion
In this module, we learned how to integrate COBOL with web services, focusing on consuming RESTful services. We covered the basics of web services, the differences between SOAP and REST, and provided practical examples and exercises. This knowledge enables you to extend the capabilities of COBOL applications by interacting with modern web services, making your programs more versatile and powerful.