DATAMONGO-884 - Improved handling for Object methods in LazyLoadingInterceptor.

We now handle invocations of equals(…)/hashCode()/toString()  methods that are not overridden with custom proxy aware logic. This avoids potentially NullPointerExceptions and makes it easier to debug code that deals with proxies (due to a proper toString representation of a proxy).

Original pull request: #158.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/DefaultDbRefResolver.java

@@ -41,6 +41,7 @@ import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.ReflectionUtils;
 import org.springframework.util.StringUtils;
 
 import com.mongodb.DB;
@@ -230,12 +231,81 @@ public class DefaultDbRefResolver implements DbRefResolver {
 				return this.dbref;
 			}
 
-			Object target = isObjectMethod(method) && Object.class.equals(method.getDeclaringClass()) ? obj
-					: ensureResolved();
+			if (isObjectMethod(method) && Object.class.equals(method.getDeclaringClass())) {
+
+				if (ReflectionUtils.isToStringMethod(method)) {
+					return proxyToString(proxy);
+				}
+
+				if (ReflectionUtils.isEqualsMethod(method)) {
+					return proxyEquals(proxy, args[0]);
+				}
+
+				if (ReflectionUtils.isHashCodeMethod(method)) {
+					return proxyHashCode(proxy);
+				}
+			}
+
+			Object target = ensureResolved();
+
+			if (target == null) {
+				return null;
+			}
 
 			return method.invoke(target, args);
 		}
 
+		/**
+		 * Returns a to string representation for the given {@code proxy}.
+		 * 
+		 * @param proxy
+		 * @return
+		 */
+		private String proxyToString(Object proxy) {
+
+			StringBuilder description = new StringBuilder();
+			if (dbref != null) {
+				description.append(dbref.getRef());
+				description.append(":");
+				description.append(dbref.getId());
+			} else {
+				description.append(System.identityHashCode(proxy));
+			}
+			description.append("$").append(LazyLoadingProxy.class.getSimpleName());
+
+			return description.toString();
+		}
+
+		/**
+		 * Returns the hashcode for the given {@code proxy}.
+		 * 
+		 * @param proxy
+		 * @return
+		 */
+		private int proxyHashCode(Object proxy) {
+			return proxyToString(proxy).hashCode();
+		}
+
+		/**
+		 * Performs an equality check for the given {@code proxy}.
+		 * 
+		 * @param proxy
+		 * @param that
+		 * @return
+		 */
+		private boolean proxyEquals(Object proxy, Object that) {
+
+			if (!(that instanceof LazyLoadingProxy)) {
+				return false;
+			}
+
+			if (that == proxy) {
+				return true;
+			}
+
+			return proxyToString(proxy).equals(that.toString());
+		}
+
 		/**
 		 * Will trigger the resolution if the proxy is not resolved already or return a previously resolved result.
 		 * 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateTests.java

@@ -61,6 +61,7 @@ import org.springframework.data.mongodb.MongoDbFactory;
 import org.springframework.data.mongodb.core.convert.CustomConversions;
 import org.springframework.data.mongodb.core.convert.DbRefResolver;
 import org.springframework.data.mongodb.core.convert.DefaultDbRefResolver;
+import org.springframework.data.mongodb.core.convert.LazyLoadingProxy;
 import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
 import org.springframework.data.mongodb.core.index.Index;
 import org.springframework.data.mongodb.core.index.Index.Duplicates;
@@ -2550,6 +2551,35 @@ public class MongoTemplateTests {
 		assertThat(savedMessage.normalContent.text, is(content.text));
 	}
 
+	/**
+	 * @see DATAMONGO-884
+	 */
+	@Test
+	public void callingNonObjectMethodsOnLazyLoadingProxyShouldReturnNullIfUnderlyingDbrefWasDeletedInbetween() {
+
+		template.dropCollection(SomeTemplate.class);
+		template.dropCollection(SomeContent.class);
+
+		SomeContent content = new SomeContent();
+		content.id = "C1";
+		content.text = "BUBU";
+		template.save(content);
+
+		SomeTemplate tmpl = new SomeTemplate();
+		tmpl.id = "T1";
+		tmpl.content = content; // @DBRef(lazy=true) tmpl.content
+
+		template.save(tmpl);
+
+		SomeTemplate savedTmpl = template.findById(tmpl.id, SomeTemplate.class);
+
+		template.remove(content);
+
+		assertThat(savedTmpl.getContent().toString(), is("someContent:C1$LazyLoadingProxy"));
+		assertThat(savedTmpl.getContent(), is(instanceOf(LazyLoadingProxy.class)));
+		assertThat(savedTmpl.getContent().getText(), is(nullValue()));
+	}
+
 	static class DocumentWithDBRefCollection {
 
 		@Id public String id;
@@ -2730,7 +2760,7 @@ public class MongoTemplateTests {
 		EnumValue value;
 	}
 
-	static class SomeTemplate {
+	public static class SomeTemplate {
 
 		String id;
 		@org.springframework.data.mongodb.core.mapping.DBRef(lazy = true) SomeContent content;
@@ -2740,10 +2770,14 @@ public class MongoTemplateTests {
 		}
 	}
 
-	static class SomeContent {
+	public static class SomeContent {
 
 		String id;
 		String text;
+
+		public String getText() {
+			return text;
+		}
 	}
 
 	static class SomeMessage {

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/DbRefMappingMongoConverterUnitTests.java

@@ -310,6 +310,93 @@ public class DbRefMappingMongoConverterUnitTests {
 		assertProxyIsResolved(result.dbRefToToStringObjectMethodOverride, true);
 	}
 
+	/**
+	 * @see DATAMONGO-884
+	 */
+	@Test
+	public void callingToStringObjectMethodOnLazyLoadingDbrefShouldNotInitializeProxy() {
+
+		String id = "42";
+		String value = "bubu";
+		MappingMongoConverter converterSpy = spy(converter);
+		doReturn(new BasicDBObject("_id", id).append("value", value)).when(converterSpy).readRef((DBRef) any());
+
+		BasicDBObject dbo = new BasicDBObject();
+		WithObjectMethodOverrideLazyDbRefs lazyDbRefs = new WithObjectMethodOverrideLazyDbRefs();
+		lazyDbRefs.dbRefToPlainObject = new LazyDbRefTarget(id, value);
+		converterSpy.write(lazyDbRefs, dbo);
+
+		WithObjectMethodOverrideLazyDbRefs result = converterSpy.read(WithObjectMethodOverrideLazyDbRefs.class, dbo);
+
+		assertThat(result.dbRefToPlainObject, is(notNullValue()));
+		assertProxyIsResolved(result.dbRefToPlainObject, false);
+
+		// calling Object#toString does not initialize the proxy.
+		String proxyString = result.dbRefToPlainObject.toString();
+		assertThat(proxyString, is("lazyDbRefTarget" + ":" + id + "$LazyLoadingProxy"));
+		assertProxyIsResolved(result.dbRefToPlainObject, false);
+
+		// calling another method not declared on object triggers proxy initialization.
+		assertThat(result.dbRefToPlainObject.getValue(), is(value));
+		assertProxyIsResolved(result.dbRefToPlainObject, true);
+	}
+
+	/**
+	 * @see DATAMONGO-884
+	 */
+	@Test
+	public void equalsObjectMethodOnLazyLoadingDbrefShouldNotInitializeProxy() {
+
+		String id = "42";
+		String value = "bubu";
+		MappingMongoConverter converterSpy = spy(converter);
+		doReturn(new BasicDBObject("_id", id).append("value", value)).when(converterSpy).readRef((DBRef) any());
+
+		BasicDBObject dbo = new BasicDBObject();
+		WithObjectMethodOverrideLazyDbRefs lazyDbRefs = new WithObjectMethodOverrideLazyDbRefs();
+		lazyDbRefs.dbRefToPlainObject = new LazyDbRefTarget(id, value);
+		lazyDbRefs.dbRefToToStringObjectMethodOverride = new ToStringObjectMethodOverrideLazyDbRefTarget(id, value);
+		converterSpy.write(lazyDbRefs, dbo);
+
+		WithObjectMethodOverrideLazyDbRefs result = converterSpy.read(WithObjectMethodOverrideLazyDbRefs.class, dbo);
+
+		assertThat(result.dbRefToPlainObject, is(notNullValue()));
+		assertProxyIsResolved(result.dbRefToPlainObject, false);
+
+		assertThat(result.dbRefToPlainObject, is(equalTo(result.dbRefToPlainObject)));
+		assertThat(result.dbRefToPlainObject, is(not(equalTo(null))));
+		assertThat(result.dbRefToPlainObject, is(not(equalTo((Object) lazyDbRefs.dbRefToToStringObjectMethodOverride))));
+
+		assertProxyIsResolved(result.dbRefToPlainObject, false);
+	}
+
+	/**
+	 * @see DATAMONGO-884
+	 */
+	@Test
+	public void hashcodeObjectMethodOnLazyLoadingDbrefShouldNotInitializeProxy() {
+
+		String id = "42";
+		String value = "bubu";
+		MappingMongoConverter converterSpy = spy(converter);
+		doReturn(new BasicDBObject("_id", id).append("value", value)).when(converterSpy).readRef((DBRef) any());
+
+		BasicDBObject dbo = new BasicDBObject();
+		WithObjectMethodOverrideLazyDbRefs lazyDbRefs = new WithObjectMethodOverrideLazyDbRefs();
+		lazyDbRefs.dbRefToPlainObject = new LazyDbRefTarget(id, value);
+		lazyDbRefs.dbRefToToStringObjectMethodOverride = new ToStringObjectMethodOverrideLazyDbRefTarget(id, value);
+		converterSpy.write(lazyDbRefs, dbo);
+
+		WithObjectMethodOverrideLazyDbRefs result = converterSpy.read(WithObjectMethodOverrideLazyDbRefs.class, dbo);
+
+		assertThat(result.dbRefToPlainObject, is(notNullValue()));
+		assertProxyIsResolved(result.dbRefToPlainObject, false);
+
+		assertThat(result.dbRefToPlainObject.hashCode(), is(311365444));
+
+		assertProxyIsResolved(result.dbRefToPlainObject, false);
+	}
+
 	/**
 	 * @see DATAMONGO-884
 	 */
@@ -513,6 +600,7 @@ public class DbRefMappingMongoConverterUnitTests {
 
 	static class WithObjectMethodOverrideLazyDbRefs {
 
+		@org.springframework.data.mongodb.core.mapping.DBRef(lazy = true) LazyDbRefTarget dbRefToPlainObject;
 		@org.springframework.data.mongodb.core.mapping.DBRef(lazy = true) ToStringObjectMethodOverrideLazyDbRefTarget dbRefToToStringObjectMethodOverride;
 		@org.springframework.data.mongodb.core.mapping.DBRef(lazy = true) EqualsAndHashCodeObjectMethodOverrideLazyDbRefTarget dbRefEqualsAndHashcodeObjectMethodOverride2;
 		@org.springframework.data.mongodb.core.mapping.DBRef(lazy = true) EqualsAndHashCodeObjectMethodOverrideLazyDbRefTarget dbRefEqualsAndHashcodeObjectMethodOverride1;