Improve Fess API implementation

[marevol]

This pull request introduces a set of significant refactoring and improvements to the Fess API implementation, focusing on modularity, maintainability, performance, and code quality. Key changes include the introduction of new utility classes for content type and JSON response handling, centralization of API constants, thread-safety improvements in the API manager factory, and simplification of content type detection logic. These changes are fully backward compatible and lay the groundwork for future enhancements.

API Infrastructure Improvements

• Introduced ApiConstants.java to centralize all API-related constants (request/response field names, HTTP methods, MIME types, error messages, etc.), eliminating magic strings and improving maintainability across the codebase.
• Refactored WebApiManagerFactory.java to use a thread-safe CopyOnWriteArrayList for storing API managers, added null validation in the add() method, and implemented a size() method for introspection. This improves performance and safety during concurrent initialization. [1] [2]

Utility and Code Simplification

• Added ContentTypeUtil.java, a new utility class that centralizes MIME type detection using a map-based approach, replacing long if-else chains for file extension handling. This makes content type management extensible and maintainable.
• Refactored content type detection in SearchEngineApiManager.java to use ContentTypeUtil, reducing ~30 lines of repetitive if-else code to ~7 lines and improving readability and extensibility.

API Manager Improvements

• Updated BaseApiManager.java to use the new ApiConstants for attribute keys and replaced the format type detection if-else chain with efficient enum-based detection using FormatType.valueOf(), improving code clarity and performance. [1] [2] [3]

For a detailed overview and rationale behind these changes, see the new documentation in API_IMPROVEMENTS.md.

[Copilot]

Pull Request Overview

This pull request refactors the Fess API implementation to improve maintainability, thread safety, and code organization. The changes introduce utility classes for content type detection and JSON response handling, centralize constants, and simplify format type detection logic while maintaining backward compatibility.

Key Changes:

• Introduced ApiConstants.java to centralize API-related constants, eliminating magic strings
• Refactored WebApiManagerFactory.java to use thread-safe CopyOnWriteArrayList for better concurrent performance
• Added ContentTypeUtil.java to simplify MIME type detection with map-based lookups

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
JsonResponseUtil.java	New utility class for centralized JSON response building and error handling
SearchEngineApiManager.java	Refactored content type detection to use new utility class
WebApiManagerFactory.java	Improved thread safety and replaced array-based storage with CopyOnWriteArrayList
ContentTypeUtil.java	New utility class for MIME type detection based on file extensions
BaseApiManager.java	Simplified format type detection using enum-based approach
ApiConstants.java	New constants class centralizing API-related string constants
API_IMPROVEMENTS.md	Documentation describing the improvements and rationale

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The map should be unmodifiable or use a thread-safe implementation since registerContentType() allows runtime modifications. Consider using ConcurrentHashMap instead of HashMap to prevent potential race conditions when registering custom content types.

[Copilot]

The regex pattern allows dots in callback names, which could enable prototype pollution attacks in older JavaScript environments. Consider removing the dot from the allowed characters: [^0-9a-zA-Z_\\$]

Suggested change

	// Only allow alphanumeric, underscore, dollar, and dot characters
	return "/**/" + callbackName.replaceAll("[^0-9a-zA-Z_\\$\\.]", StringUtil.EMPTY);
	// Only allow alphanumeric, underscore, and dollar characters
	return "/**/" + callbackName.replaceAll("[^0-9a-zA-Z_\\$]", StringUtil.EMPTY);

[Copilot]

[nitpick] The initial capacity of 100 may be insufficient for stack traces, which can be much longer. Consider using a larger initial capacity (e.g., 512 or 1024) to reduce reallocations.

Suggested change

	final StringBuilder buf = new StringBuilder(100);
	final StringBuilder buf = new StringBuilder(1024);