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commit 2fcb104294b2676154cb08f00d5665d668792280
Author: Mark Thomas <ma...@apache.org>
AuthorDate: Thu Jul 8 22:02:26 2021 +0100
Add support for coercing LambdaExpression to any functional interface
This addresses this currently open issue against the EL spec
https://github.com/eclipse-ee4j/el-ri/issues/45
This is an initial implementation so users can provide feedback
The implementation was inspired by rmuller's suggestion for an
ELResolver that performs a similar function:
https://stackoverflow.com/questions/46573761
---
java/org/apache/el/LocalStrings.properties | 2 +
java/org/apache/el/lang/ELSupport.java | 27 +++++++++++
test/org/apache/el/lang/TestELSupport.java | 76 ++++++++++++++++++++++++++++++
webapps/docs/changelog.xml | 5 ++
4 files changed, 110 insertions(+)
diff --git a/java/org/apache/el/LocalStrings.properties
b/java/org/apache/el/LocalStrings.properties
index 1bf600d..d9f5503 100644
--- a/java/org/apache/el/LocalStrings.properties
+++ b/java/org/apache/el/LocalStrings.properties
@@ -13,6 +13,8 @@
# See the License for the specific language governing permissions and
# limitations under the License.
+elSupport.coerce.nonAbstract=Unable to coerce a LambdaExpression to the
functional interface [{0}] because the method [{1}] is not abstract
+
# General Errors
error.cannotSetVariables=Cannot set variables on factory
error.convert=Cannot convert [{0}] of type [{1}] to [{2}]
diff --git a/java/org/apache/el/lang/ELSupport.java
b/java/org/apache/el/lang/ELSupport.java
index 808ad79..c37fbac 100644
--- a/java/org/apache/el/lang/ELSupport.java
+++ b/java/org/apache/el/lang/ELSupport.java
@@ -19,6 +19,9 @@ package org.apache.el.lang;
import java.beans.PropertyEditor;
import java.beans.PropertyEditorManager;
import java.lang.reflect.Array;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+import java.lang.reflect.Proxy;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.security.AccessController;
@@ -29,6 +32,7 @@ import java.util.Set;
import jakarta.el.ELContext;
import jakarta.el.ELException;
+import jakarta.el.LambdaExpression;
import org.apache.el.util.MessageFactory;
@@ -588,6 +592,11 @@ public class ELSupport {
return result;
}
+ if (obj instanceof LambdaExpression &&
type.getAnnotation(FunctionalInterface.class) != null) {
+ T result = coerceToFunctionalInterface(ctx, (LambdaExpression)
obj, type);
+ return result;
+ }
+
throw new ELException(MessageFactory.get("error.convert",
obj, obj.getClass(), type));
}
@@ -613,6 +622,24 @@ public class ELSupport {
return result;
}
+
+ private static <T> T coerceToFunctionalInterface(final ELContext ctx,
final LambdaExpression lambdaExpression,
+ final Class<T> type) {
+ // Create a dynamic proxy for the functional interface
+ @SuppressWarnings("unchecked")
+ T result = (T) Proxy.newProxyInstance(type.getClassLoader(), new
Class[] { type },
+ (Object obj, Method method, Object[] args) -> {
+ // Functional interfaces have a single, abstract method
+ if (!Modifier.isAbstract(method.getModifiers())) {
+ // TODO
+ throw new
ELException(MessageFactory.get("elSupport.coerce.nonAbstract", type, method));
+ }
+ return lambdaExpression.invoke(ctx, args);
+ });
+ return result;
+ }
+
+
public static final boolean isBigDecimalOp(final Object obj0,
final Object obj1) {
return (obj0 instanceof BigDecimal || obj1 instanceof BigDecimal);
diff --git a/test/org/apache/el/lang/TestELSupport.java
b/test/org/apache/el/lang/TestELSupport.java
index 84d3ed4..672afd5 100644
--- a/test/org/apache/el/lang/TestELSupport.java
+++ b/test/org/apache/el/lang/TestELSupport.java
@@ -19,9 +19,11 @@ package org.apache.el.lang;
import java.beans.PropertyEditorManager;
import java.math.BigDecimal;
import java.math.BigInteger;
+import java.util.function.Predicate;
import jakarta.el.ELException;
import jakarta.el.ELManager;
+import jakarta.el.ELProcessor;
import org.junit.Assert;
import org.junit.Test;
@@ -276,4 +278,78 @@ public class TestELSupport {
VALB1,
VALB2
}
+
+
+ @Test
+ public void testCoercetoFunctionalInterface01() throws Exception {
+ final ELProcessor elp = new ELProcessor();
+ elp.defineFunction("", "", "org.apache.el.lang.TestELSupport",
"testPredicateA");
+ Object result = elp.eval("testPredicateA(x -> x.equals('data'))");
+ Assert.assertEquals("PASS", result);
+ }
+
+
+ @Test
+ public void testCoercetoFunctionalInterface02() throws Exception {
+ final ELProcessor elp = new ELProcessor();
+ elp.defineFunction("", "", "org.apache.el.lang.TestELSupport",
"testPredicateA");
+ Object result = elp.eval("testPredicateA(x -> !x.equals('data'))");
+ Assert.assertEquals("BLOCK", result);
+ }
+
+
+ @Test
+ public void testCoercetoFunctionalInterface03() throws Exception {
+ final ELProcessor elp = new ELProcessor();
+ elp.defineFunction("", "", "org.apache.el.lang.TestELSupport",
"testPredicateB");
+ Object result = elp.eval("testPredicateB(x -> x > 50)");
+ Assert.assertEquals("PASS", result);
+ }
+
+
+ @Test
+ public void testCoercetoFunctionalInterface04() throws Exception {
+ final ELProcessor elp = new ELProcessor();
+ elp.defineFunction("", "", "org.apache.el.lang.TestELSupport",
"testPredicateB");
+ Object result = elp.eval("testPredicateB(x -> x < 50)");
+ Assert.assertEquals("BLOCK", result);
+ }
+
+
+ @Test(expected = ELException.class)
+ public void testCoercetoFunctionalInterface05() throws Exception {
+ final ELProcessor elp = new ELProcessor();
+ elp.defineFunction("", "", "org.apache.el.lang.TestELSupport",
"testPredicateC");
+ elp.eval("testPredicateC(x -> x > 50)");
+ }
+
+
+ public static String testPredicateA(Predicate<String> filter) {
+ String s = "data";
+ if (filter.test(s)) {
+ return "PASS";
+ } else {
+ return "BLOCK";
+ }
+ }
+
+
+ public static String testPredicateB(Predicate<Long> filter) {
+ Long l = Long.valueOf(100);
+ if (filter.test(l)) {
+ return "PASS";
+ } else {
+ return "BLOCK";
+ }
+ }
+
+
+ public static String testPredicateC(Predicate<String> filter) {
+ String s = "text";
+ if (filter.test(s)) {
+ return "PASS";
+ } else {
+ return "BLOCK";
+ }
+ }
}
diff --git a/webapps/docs/changelog.xml b/webapps/docs/changelog.xml
index 2e78aa9..4cec1f7 100644
--- a/webapps/docs/changelog.xml
+++ b/webapps/docs/changelog.xml
@@ -148,6 +148,11 @@
Add additional generics to the EL API to align with the latest changes
in the EL specification project. (markt)
</scode>
+ <add>
+ Enable EL lambda expressions to be coerced to functional interfaces.
+ This is an implementation of a proposed extension to the Jakarta
+ Expression Language specification. (markt)
+ </add>
</changelog>
</subsection>
<subsection name="Web applications">
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