Introduce Supplier<String> message support in org.springframework.util.Assert [SPR-14450]

[spring-projects-issues]

Sam Brannen opened SPR-14450 and commented

1. Introduce overloaded methods in org.springframework.util.Assert that accept Supplier<String> instead of String for lazy evaluation of error messages.

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Affects: 5.0 M1

Issue Links:

• Revisit Assert to avoid single-arg assert methods (with refined messages) [SPR-15196] #19761 Revisit Assert to avoid single-arg assert methods (with refined messages)

Referenced from: commits 68b3bc0, 264f586, 17dd5dd

[spring-projects-issues]

Sam Brannen commented

Resolved in GitHub commit 17dd5dd:

Introduce Supplier support in Assert util

Prior to this commit, utility methods in org.springframework.util.Assert accepted String arguments for custom error messages. Such Strings are evaluated (e.g., concatenated) eagerly, and for performance reasons, it was therefore not always possible to make use of these utility methods. Consequently, there are several places in the code base that "inline" identical functionality in order to lazily evaluate error message concatenation and avoid an unnecessary performance penalty. This leads to verbose code like the following.

if (!contextPath.startsWith("/")) {
    throw new IllegalArgumentException("contextPath '" + contextPath +
    "' must start with '/'.");
}
if (contextPath.endsWith("/")) {
    throw new IllegalArgumentException("contextPath '" + contextPath + 
    "' must not end with '/'.");
}

This commit addresses this shortcoming by introducing Supplier<String> variants of all utility methods in org.springframework.util.Assert that allow custom error messages to be evaluated lazily via a lambda expression that is only evaluated if the assertion fails. This results in a simplification of the previous examples as follows.

Assert.isTrue(contextPath.startsWith("/"), () -> "contextPath '" + 
    contextPath + "' must start with '/'.");
Assert.isTrue(!contextPath.endsWith("/"), () -> "contextPath '" + 
    contextPath + "' must not end with '/'.");