API compatibility with lambda expressions [SPR-9640]

[spring-projects-issues]

Juergen Hoeller opened SPR-9640 and commented

http://openjdk.java.net/jeps/126

Consider marking all applicable Spring callback interfaces with Java 8's @FunctionalInterface. Even if that marker basically just works as a compiler assertion along the lines of @Override, it might still be worth using it consistently as a formal documentation measure. Applicable Spring interfaces can then by found by that marker and will be documented as such in javadoc.

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This issue is a sub-task of #14273

0 votes, 6 watchers

[spring-projects-issues]

Juergen Hoeller commented

We're not adding @FunctionalInterface for the time being, since it would only buy us a documentation effect but introduces a risk for potential class loading issues on older JVMs. Even if, technically, a JVM should ignore a declared annotation if it cannot find the annotation type in the classpath, there may be unpleasant warnings or the like displayed on non-Sun/Oracle JVMs.

In all other respects, the obvious candidate interfaces in the core codebase are all naturally compliant with Java 8's rules. There are a few niche interfaces that declare more than one method (e.g. BatchPreparedStatementSetter) and a few base implementations of callback interfaces that declare a different abstract template method (e.g. AbstractLobStreamingResultSetExtractor); however, we're not considering those as important enough to split them into their own functional interface variant.