SOAP API とは？
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- SOAP API とは？
Simple Object Access Protocol API, more commonly referred to as SOAP API, is a type of web service protocol that allows different applications to communicate with each other over the internet. SOAP API uses XML to format messages and enforces strict rules for how data is sent and received. Because of this structured approach, SOAP APIs are commonly used in enterprise systems where secure, reliable communication is critical.
How SOAP APIs work
SOAP APIs operate by sending and receiving messages encoded in XML over internet protocols like HTTP, HTTPS or SMTP. Each request and response must follow a strict structure defined by the Web Services Description Language (WSDL), which specifies the available operations, message formats and data types.
Think of a SOAP API as sending a certified letter through the postal service. The message (your data) must be placed in a properly formatted envelope (the SOAP structure) and follow strict delivery protocols. This rigidity makes SOAP APIs ideal for high-security environments where standardized communication is crucial to protecting sensitive data.
Key features of SOAP APIs
SOAP APIs are valued for their strict structure and ability to function across different systems. Here are the main features that make SOAP API a strong choice for enterprises:
Strict XML-based messaging: All data is formatted in XML, and each message must follow a schema defined in WSDL, ensuring consistency in communication between systems.
Language and platform-agnostic: Ideal for versatile technologies, SOAP APIs work across different programming languages and operating systems.
Built-in error handling: Responses include detailed error codes and descriptions, helping developers detect and resolve issues more efficiently.
Supports both stateless and stateful operations: SOAP API supports both stateless (no memory of past requests) and stateful (retained session data over time) operations, depending on the system's needs.
Protocol-independent: While most commonly used over HTTP, SOAP APIs can also use other protocols like SMTP or TCP, allowing for more flexible communication.
SOAP API vs REST API
Both SOAP and REST APIs enable communication between systems over a network, but they differ in their approach:
| SOAP API | REST API |
|---|---|
| Message format | |
| Uses XML only | Supports multiple formats (JSON, XML, HTML, plaintext, etc.) |
| プロトコル | |
| Protocol-independent; works over HTTP, SMTP, etc. | HTTP-based only |
| Style | |
| Focuses on the message | Focuses on the message |
| Speed | |
| Slower due to strict formatting | Faster due to lightweight data formats |
| State handling | |
| Supports stateless and stateful operations | Generally stateless |
| 活用事例 | |
| Ideal for enterprise-level applications, banks and governments | Ideal for mobile apps, public APIs and web applications |
Continuing with the analogy above, SOAP API is like sending a physical letter in a sealed envelope through the postal system; it's secure and follows formal rules to ensure the message arrives properly, but it can be slow. REST API, on the other hand, is like sending a text message; it's fast and convenient but also less secure.
Risks of using SOAP APIs
While SOAP APIs offer strong security, they may not be ideal for all use cases, especially in fast-paced environments. Here are the main security risks to consider when using a SOAP API:
No support for caching API calls: Unlike REST APIs, SOAP APIs do not support caching, leading to slower performance and increased issues on servers.
Complex to implement: Due to its strict structure and reliance on WSDL, SOAP APIs require a deeper understanding to test and debug compared to REST APIs.
Slow and not very adaptable: Because of its XML-based messaging and rigid guidelines, a SOAP API is typically slower and less adaptable than a REST API, making it less suitable for applications that favor flexible data formats.
Benefits of using SOAP APIs
Despite being complex and strict, SOAP APIs offer multiple benefits in enterprise environments, including high security for sensitive data, reliability in distributed work environments and built-in error handling.
High security for sensitive data
One of the most important benefits of a SOAP API is its support for strong security standards, such as WS-Security. This allows for message-level encryption and secure token handling, making SOAP APIs well-suited for handling sensitive information. Because of this, the financial industry and government services rely on SOAP APIs to ensure sensitive data is transmitted securely and to meet compliance requirements.
Reliable in distributed work environments
SOAP APIs are well-suited for enterprise-level, distributed systems where different services must interact across various networks, platforms or geographic regions. Due to their protocol-agnostic nature, SOAP APIs can send data not only over HTTP but also through SMTP, TCP and other protocols for greater flexibility.
Built-in error handling
Rather than vague failure messages, SOAP APIs return structured messages that include error codes and human-readable descriptions to help developers debug issues quickly. SOAP APIs improve the overall reliability of a system, since failures can be easily traced and corrected with precision.
SOAP API use cases
For many industries and systems, SOAP APIs are ideal for high-security, strict data transfer and reliable communication across multiple services. Here are some of the most common real-world use cases where SOAP APIs are applied.
Bank transfers
Bank transfers usually require communication between several financial institutions, including banks and payment processors. SOAP APIs are generally used for this because they provide a standardized way to securely exchange data between systems, ensuring each transaction is accurately processed. For example, transferring money may involve calling web services to verify account details, check available funds and complete the transaction. SOAP APIs' strict messaging format ensures that all of the involved steps happen reliably and reduces the risk of transactional errors or data leaks.
Flight bookings
Booking a flight involves several web services working together, from checking seat availability to retrieving current pricing. Different airline systems or third-party vendors may handle each task. SOAP APIs are used when booking flights because they support multi-step processes and can manage stateful operations when needed. In this scenario, they can hold a flight reservation while the payment is processing and ensure frequent updates to maintain the most accurate pricing and availability.
Navigation and shipping companies
Logistics companies rely on real-time data from many external sources, like weather services and traffic data providers. SOAP APIs are ideal for these scenarios because they provide a reliable way to gather data from multiple web services. For example, a shipping company may use SOAP APIs to calculate the fastest route by using data from mapping systems and current road conditions while ensuring secure data exchange.
