Support Conditional Parameter Expansion

[gromspys]

Issue: #521

Summary by CodeRabbit

• New Feature: Enhanced support for Optional variables in our core functionality. This allows for more flexible handling of variables, improving the software's adaptability to different data scenarios.
• Test: Expanded our test coverage to include scenarios with optional parameters. This ensures our software remains reliable and robust, even when dealing with complex or unusual data inputs.
• Usability: The software now handles empty Optional variables more intuitively, reducing potential confusion and making the software easier to use.

[coderabbitai]

Walkthrough

The changes introduce support for Optional variables in the expand method of the Expressions class, enhancing the flexibility of variable handling. Additionally, new test scenarios have been added to ensure the correct functioning of optional parameters in different states.

Changes

File Path	Summary
.../feign/template/Expressions.java	Added support for Optional variables in the expand method. Handles both present and empty Optional variables based on the nameRequired flag.
.../feign/spring/SpringContractTest.java	Introduced new test methods and mockClient configurations to cover various scenarios of optional parameters. Added a new method to handle the /optional endpoint with an optional query parameter.

🐇💻

In the land of code, where the brackets lie,

Optional variables, under the compiler's eye.

Tests run in the spring, under the moon's glow,

Ensuring our code, continues to flow. 🌙🌟

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[coderabbitai]

Review Status

Actionable comments generated: 0

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Commits

Files that changed from the base of the PR and between 4520f62 and 98fef61.

Files selected for processing (2)

• core/src/main/java/feign/template/Expressions.java (2} hunks)
• spring4/src/test/java/feign/spring/SpringContractTest.java (3} hunks)

Additional comments: 5

spring4/src/test/java/feign/spring/SpringContractTest.java (3)

• 57-59: The new mock client setup includes additional endpoints for testing optional parameters. This is in line with the PR's goal of introducing support for conditional parameter expansion in Feign, specifically handling Optional variables.

• 121-147: These new test methods are designed to validate the handling of Optional parameters in different scenarios: when the Optional is present, not present, empty, and nullable. Each test method makes a request to the checkWithOptional method of the Resource interface with different Optional parameters and verifies the expected HTTP request sent by the client. This is a good practice as it ensures that the new functionality works as expected in different scenarios.

• 287-289: The checkWithOptional method has been added to the Resource interface to handle the /health/optional endpoint. It takes an Optional<String> parameter, which is annotated with @RequestParam. This is consistent with the PR's goal of adding support for Optional parameters in Feign.

core/src/main/java/feign/template/Expressions.java (2)

• 20-20: The java.util.Optional import has been added to handle Optional variables in the URI template expressions.

• 158-168: The code has been updated to handle Optional variables. If the variable is present, it is expanded recursively. If the variable is empty and nameRequired is false, null is returned. If nameRequired is true, the encoded name is appended to the expanded string.

+      } else if (Optional.class.isAssignableFrom(variable.getClass())) {
+        Optional<?> optional = (Optional) variable;
+        if (optional.isPresent()) {
+          expanded.append(this.expand(optional.get(), encode));
+        } else {
+          if (!this.nameRequired) {
+            return null;
+          }
+          expanded.append(this.encode(this.getName()))
+                  .append("=");
+        }
+      } else {

While the changes are correct, it's worth noting that returning null from a method that is expected to return a String can lead to NullPointerExceptions in the calling code if not handled properly. Consider returning an empty string instead of null to avoid potential issues.

Committable suggestion (Beta)

      } else if (Optional.class.isAssignableFrom(variable.getClass())) {
        Optional<?> optional = (Optional) variable;
        if (optional.isPresent()) {
          expanded.append(this.expand(optional.get(), encode));
        } else {
          if (!this.nameRequired) {
            return "";
          }
          expanded.append(this.encode(this.getName()))
                  .append("=");
        }
      } else {