IncompatibleClassChangeError encountered on execution of compiled SPEL expressions

[Smahlatz]

Affects: 5.1.12, 5.2.2

---

Since this change in 5.1.8.RELEASE (#22242) we are witnessing failures in evaluation of compiled SpEL expressions.

The following test exposes the issue:

    public void compiledExpression_typeDeclaresInterface() {
        final SpelParserConfiguration config = new SpelParserConfiguration(SpelCompilerMode.IMMEDIATE, null);
        SpelExpressionParser parser = new SpelExpressionParser(config);
        final Expression expression = parser.parseExpression("name");
        Person barney = new Person("Barney");
        assertThat(expression.getValue(barney), is("Barney"));
        assertThat(expression.getValue(barney), is("Barney"));
        //This time the compiled expression will be used
        assertThat(expression.getValue(barney), is("Barney"));
    }

    public static class Person implements Named {

        private final String name;

        public Person(final String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }
    }

    public interface Named {
        String getName();
    }

Running this results in the following exception:

org.springframework.expression.spel.SpelEvaluationException: EL1072E: An exception occurred whilst evaluating a compiled expression
	at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:194)
	at org.springframework.expression.spel.support.CompiledSpelExpressionTest.compiledExpression_typeDeclaresInterface(CompiledSpelExpressionTest.java:24)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: java.lang.IncompatibleClassChangeError: Found interface org.springframework.expression.spel.support.CompiledSpelExpressionTest$Named, but class was expected
	at spel.Ex2.getValue(Unknown Source)
	at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:184)

The issue looks to be with the compilation - org.springframework.expression.spel.support.ReflectivePropertyAccessor.generateCode contains the following:

            if (this.member instanceof Method) {

                mv.visitMethodInsn((isStatic ? INVOKESTATIC :  INVOKEVIRTUAL), classDesc, this.member.getName(),
                        CodeFlow.createSignatureDescriptor((Method) this.member). false);
            }

As we now are potentially referencing an interface, the following change fixes the issue:

            if (this.member instanceof Method) {

                boolean isInterface = this.member.getDeclaringClass().isInterface();
                mv.visitMethodInsn((isStatic ? INVOKESTATIC : isInterface ? INVOKEINTERFACE : INVOKEVIRTUAL), classDesc, this.member.getName(),
                        CodeFlow.createSignatureDescriptor((Method) this.member), isInterface);
            }

This has been tested against Oracle JDK 8u231 and spring-expression 5.1.12.RELEASE and 5.2.2.RELEASE. The issue is not encountered in spring-expression 5.1.7 and below.

[sbrannen]

I've edited your comment to improve the formatting. You might want to check out this Mastering Markdown guide for future reference.

[sbrannen]

Thanks for raising the issue.

@Smahlatz, would you be interested in submitting a PR with your patch and your test?

[Smahlatz]

@sbrannen I would certainly be interested in submitting a PR, however my current terms of employment make this problematic.

[sbrannen]

@sbrannen I would certainly be interested in submitting a PR, however my current terms of employment make this problematic.

Understood.

May we use your test case?

Never mind: I've implemented a simplified version.

[sbrannen]

I have confirmed that the following test case fails on master.

Interestingly, the test only fails if the interface is public.

import java.util.stream.IntStream;

import org.junit.jupiter.api.Test;

import org.springframework.core.Ordered;
import org.springframework.expression.Expression;
import org.springframework.expression.spel.SpelCompilerMode;
import org.springframework.expression.spel.SpelParserConfiguration;
import org.springframework.expression.spel.standard.SpelCompiler;
import org.springframework.expression.spel.standard.SpelExpressionParser;

import static org.assertj.core.api.Assertions.assertThat;

/**
 * Tests for the {@link SpelCompiler}.
 *
 * @since 5.1.14
 */
class SpelCompilerTests {

	@Test // gh-24357
	void expressionCompilesWhenMethodComesFromPublicInterface() {
		SpelParserConfiguration config = new SpelParserConfiguration(SpelCompilerMode.IMMEDIATE, null);
		SpelExpressionParser parser = new SpelExpressionParser(config);

		OrderedComponent component = new OrderedComponent();
		Expression expression = parser.parseExpression("order");
		
		// Evaluate the expression multiple times to ensure that it gets compiled.
		IntStream.rangeClosed(1, 5).forEach(i -> assertThat(expression.getValue(component)).isEqualTo(42));
	}


	static class OrderedComponent implements Ordered {

		@Override
		public int getOrder() {
			return 42;
		}
	}

}

Whereas, the following JUnit 4 based test case passes against the v5.1.7.RELEASE tag and fails against the v5.1.8.RELEASE tag.

import java.util.stream.IntStream;

import org.junit.Test;

import org.springframework.core.Ordered;
import org.springframework.expression.Expression;
import org.springframework.expression.spel.SpelCompilerMode;
import org.springframework.expression.spel.SpelParserConfiguration;

import static org.junit.Assert.assertEquals;

public class SpelCompilerTests {

	@Test // gh-24357
	public void expressionCompilesWhenMethodComesFromPublicInterface() {
		SpelParserConfiguration config = new SpelParserConfiguration(SpelCompilerMode.IMMEDIATE, null);
		SpelExpressionParser parser = new SpelExpressionParser(config);

		OrderedComponent component = new OrderedComponent();
		Expression expression = parser.parseExpression("order");
		
		// Evaluate the expression multiple times to ensure that it gets compiled.
		IntStream.rangeClosed(1, 5).forEach(i -> assertEquals(42, expression.getValue(component)));
	}


	static class OrderedComponent implements Ordered {

		@Override
		public int getOrder() {
			return 42;
		}
	}

}

[Smahlatz]

@sbrannen Regarding the public interface - that's right - if not marked public, expression.isCompilable returns false and no compilation happens.

[sbrannen]

This has been fixed, to be included in 5.2.4 and backported to 5.1.14.

Feel free to try out the fix in upcoming snapshot builds for those versions.