GH-3418: Fix Poller Undeclared Checked Exceptions

Resolves #3418

`Class.newInstance()` can propagate checked exceptions that are not declared.

**cherry-pick/back-port to 5.3.x, 5.2.x, 4.3.x**

spring-integration-core/src/main/java/org/springframework/integration/endpoint/AbstractPollingEndpoint.java

@@ -58,6 +58,7 @@
 import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ErrorHandler;
+import org.springframework.util.ReflectionUtils;
 
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -402,7 +403,7 @@ private Message<?> pollForMessage() {
 
 	private Message<?> doPoll() {
 		IntegrationResourceHolder holder = bindResourceHolderIfNecessary(getResourceKey(), getResourceToBind());
-		Message<?> message;
+		Message<?> message = null;
 		try {
 			message = receiveMessage();
 		}
@@ -414,7 +415,7 @@ private Message<?> doPoll() {
 				return null;
 			}
 			else {
-				throw (RuntimeException) e;
+				ReflectionUtils.rethrowRuntimeException(e);
 			}
 		}
 

spring-integration-core/src/test/java/org/springframework/integration/endpoint/SourcePollingChannelAdapterTests.java

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.endpoint;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+import java.lang.reflect.UndeclaredThrowableException;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import org.aopalliance.intercept.MethodInterceptor;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.integration.config.EnableIntegration;
+import org.springframework.integration.core.MessageSource;
+import org.springframework.integration.dsl.IntegrationFlow;
+import org.springframework.integration.dsl.IntegrationFlows;
+import org.springframework.integration.dsl.Pollers;
+import org.springframework.lang.Nullable;
+import org.springframework.messaging.Message;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+/**
+ * @author Gary Russell
+ * @since 4.3.23
+ *
+ */
+@SpringJUnitConfig
+@DirtiesContext
+public class SourcePollingChannelAdapterTests {
+
+	@Autowired
+	Config config;
+
+	@Test
+	void undeclaredCheckedException() throws InterruptedException {
+		assertThat(this.config.latchl.await(10, TimeUnit.SECONDS)).isTrue();
+		assertThat(this.config.caught).isInstanceOf(UndeclaredThrowableException.class);
+	}
+
+	@Configuration
+	@EnableIntegration
+	public static class Config {
+
+		volatile Exception caught;
+
+		volatile CountDownLatch latchl = new CountDownLatch(1);
+
+		@Bean
+		public IntegrationFlow flow() {
+			return IntegrationFlows.from(new BadMessageSource(), e -> e.poller(Pollers.fixedDelay(500)
+					.advice(exceptionCaptor())))
+					.nullChannel();
+		}
+
+		private MethodInterceptor exceptionCaptor() {
+			return invocation -> {
+				try {
+					return invocation.proceed();
+				}
+				catch (Exception e) {
+					Config.this.caught = e;
+					throw e;
+				}
+				finally {
+					Config.this.latchl.countDown();
+				}
+			};
+		}
+
+	}
+
+	public static class BadMessageSource implements MessageSource<String> {
+
+		@Override
+		@Nullable
+		public Message<String> receive() {
+			try {
+				Foo.class.newInstance();
+			}
+			catch (InstantiationException | IllegalAccessException e) {
+			}
+			return null;
+		}
+
+	}
+
+	public static class Foo {
+
+		public Foo() throws IOException {
+			throw new IOException();
+		}
+
+	}
+
+}
+