Replace isAssignableFrom() with isInstance() where feasible

build-plugin/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/StartMojo.java

@@ -233,7 +233,7 @@ private class CreateJmxConnector implements Callable<@Nullable JMXConnector> {
 		}
 
 		private boolean hasCauseWithType(Throwable t, Class<? extends Exception> type) {
-			return type.isAssignableFrom(t.getClass()) || t.getCause() != null && hasCauseWithType(t.getCause(), type);
+			return type.isInstance(t) || t.getCause() != null && hasCauseWithType(t.getCause(), type);
 		}
 
 	}

config/checkstyle/checkstyle.xml

@@ -88,6 +88,18 @@
 				value="Please use static AssertJ imports." />
 			<property name="ignoreComments" value="true" />
 		</module>
+		<module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+			<property name="maximum" value="0"/>
+			<property name="format" value="\.isAssignableFrom\(.+\.getClass\(\)\)" />
+			<property name="message" value="Please use type.isInstance(object) instead." />
+			<property name="ignoreComments" value="true" />
+		</module>
+		<module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+			<property name="maximum" value="0"/>
+			<property name="format" value="\w+\.class\.isInstance\(.+\)" />
+			<property name="message" value="Please use object instanceof type instead." />
+			<property name="ignoreComments" value="true" />
+		</module>
 		<module name="io.spring.javaformat.checkstyle.check.SpringJavadocCheck">
 			<property name="publicOnlySinceTags" value="true" />
 			<property name="requireSinceTag" value="true" />

configuration-metadata/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/fieldvalues/javac/ExpressionTree.java

@@ -55,14 +55,14 @@ String getKind() throws Exception {
 	}
 
 	Object getLiteralValue() throws Exception {
-		if (this.literalTreeType.isAssignableFrom(getInstance().getClass())) {
+		if (this.literalTreeType.isInstance(getInstance())) {
 			return this.literalValueMethod.invoke(getInstance());
 		}
 		return null;
 	}
 
 	Object getFactoryValue() throws Exception {
-		if (this.methodInvocationTreeType.isAssignableFrom(getInstance().getClass())) {
+		if (this.methodInvocationTreeType.isInstance(getInstance())) {
 			List<?> arguments = (List<?>) this.methodInvocationArgumentsMethod.invoke(getInstance());
 			if (arguments.size() == 1) {
 				return new ExpressionTree(arguments.get(0)).getLiteralValue();
@@ -72,7 +72,7 @@ Object getFactoryValue() throws Exception {
 	}
 
 	Member getSelectedMember() throws Exception {
-		if (this.memberSelectTreeType.isAssignableFrom(getInstance().getClass())) {
+		if (this.memberSelectTreeType.isInstance(getInstance())) {
 			String expression = this.memberSelectTreeExpressionMethod.invoke(getInstance()).toString();
 			String identifier = this.memberSelectTreeIdentifierMethod.invoke(getInstance()).toString();
 			if (expression != null && identifier != null) {
@@ -83,7 +83,7 @@ Member getSelectedMember() throws Exception {
 	}
 
 	List<? extends ExpressionTree> getArrayExpression() throws Exception {
-		if (this.newArrayTreeType.isAssignableFrom(getInstance().getClass())) {
+		if (this.newArrayTreeType.isInstance(getInstance())) {
 			List<?> elements = (List<?>) this.arrayValueMethod.invoke(getInstance());
 			List<ExpressionTree> result = new ArrayList<>();
 			if (elements == null) {

core/spring-boot/src/main/java/org/springframework/boot/diagnostics/analyzer/AbstractInjectionFailureAnalyzer.java

@@ -64,7 +64,7 @@ public abstract class AbstractInjectionFailureAnalyzer<T extends Throwable> exte
 		Throwable candidate = root;
 		C result = null;
 		while (candidate != null) {
-			if (type.isAssignableFrom(candidate.getClass())) {
+			if (type.isInstance(candidate)) {
 				result = (C) candidate;
 			}
 			candidate = candidate.getCause();

core/spring-boot/src/main/java/org/springframework/boot/json/AbstractJsonParser.java

@@ -55,7 +55,7 @@ protected final <T> T tryParse(Callable<T> parser, Class<? extends Exception> ch
 			return parser.call();
 		}
 		catch (Exception ex) {
-			if (check.isAssignableFrom(ex.getClass())) {
+			if (check.isInstance(ex)) {
 				throw new JsonParseException(ex);
 			}
 			ReflectionUtils.rethrowRuntimeException(ex);

module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/context/properties/ConfigurationPropertiesReportEndpoint.java

@@ -337,7 +337,7 @@ else if (item instanceof List) {
 		if (value == null || ClassUtils.isPrimitiveOrWrapper(value.getClass()) || value instanceof String) {
 			return value;
 		}
-		if (CharSequence.class.isAssignableFrom(value.getClass())) {
+		if (value instanceof CharSequence) {
 			return value.toString();
 		}
 		return "Complex property value " + value.getClass().getName();

module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/env/EnvironmentEndpoint.java

@@ -208,11 +208,10 @@ private void extract(String root, Map<String, PropertySource<?>> map, PropertySo
 	}
 
 	protected @Nullable Object stringifyIfNecessary(@Nullable Object value) {
-		if (value == null || ClassUtils.isPrimitiveOrWrapper(value.getClass())
-				|| Number.class.isAssignableFrom(value.getClass())) {
+		if (value == null || ClassUtils.isPrimitiveOrWrapper(value.getClass()) || value instanceof Number) {
 			return value;
 		}
-		if (CharSequence.class.isAssignableFrom(value.getClass())) {
+		if (value instanceof CharSequence) {
 			return value.toString();
 		}
 		return "Complex property type " + value.getClass().getName();

module/spring-boot-http-codec/src/test/java/org/springframework/boot/http/codec/autoconfigure/CodecsAutoConfigurationTests.java

@@ -169,7 +169,7 @@ private <T> T findEncoder(AssertableApplicationContext context, Class<T> encoder
 			.filter((writer) -> writer instanceof EncoderHttpMessageWriter<?>)
 			.map((writer) -> (EncoderHttpMessageWriter<?>) writer)
 			.map(EncoderHttpMessageWriter::getEncoder)
-			.filter((encoder) -> encoderClass.isAssignableFrom(encoder.getClass()))
+			.filter(encoderClass::isInstance)
 			.findFirst()
 			.orElseThrow();
 	}

module/spring-boot-http-converter/src/test/java/org/springframework/boot/http/converter/autoconfigure/HttpMessageConvertersAutoConfigurationTests.java

@@ -465,18 +465,14 @@ private ApplicationContextRunner allOptionsRunner() {
 
 	private void assertConverterIsRegistered(AssertableApplicationContext context,
 			Class<? extends HttpMessageConverter<?>> converterType) {
-		assertThat(getClientConverters(context)).filteredOn((c) -> converterType.isAssignableFrom(c.getClass()))
-			.hasSize(1);
-		assertThat(getServerConverters(context)).filteredOn((c) -> converterType.isAssignableFrom(c.getClass()))
-			.hasSize(1);
+		assertThat(getClientConverters(context)).filteredOn(converterType::isInstance).hasSize(1);
+		assertThat(getServerConverters(context)).filteredOn(converterType::isInstance).hasSize(1);
 	}
 
 	private void assertConverterIsNotRegistered(AssertableApplicationContext context,
 			Class<? extends HttpMessageConverter<?>> converterType) {
-		assertThat(getClientConverters(context)).filteredOn((c) -> converterType.isAssignableFrom(c.getClass()))
-			.isEmpty();
-		assertThat(getServerConverters(context)).filteredOn((c) -> converterType.isAssignableFrom(c.getClass()))
-			.isEmpty();
+		assertThat(getClientConverters(context)).filteredOn(converterType::isInstance).isEmpty();
+		assertThat(getServerConverters(context)).filteredOn(converterType::isInstance).isEmpty();
 	}
 
 	private void assertBeanExists(AssertableApplicationContext context, Class<?> type, String beanName) {
@@ -504,7 +500,7 @@ private HttpMessageConverters getServerConverters(ApplicationContext context) {
 	private <T extends HttpMessageConverter<?>> T findConverter(HttpMessageConverters converters,
 			Class<? extends HttpMessageConverter<?>> type) {
 		for (HttpMessageConverter<?> converter : converters) {
-			if (type.isAssignableFrom(converter.getClass())) {
+			if (type.isInstance(converter)) {
 				return (T) converter;
 			}
 		}
@@ -589,8 +585,7 @@ static class JacksonConverterConfig {
 
 		@Bean
 		JacksonJsonHttpMessageConverter customJacksonMessageConverter(JsonMapper jsonMapperMapper) {
-			JacksonJsonHttpMessageConverter converter = new JacksonJsonHttpMessageConverter(jsonMapperMapper);
-			return converter;
+			return new JacksonJsonHttpMessageConverter(jsonMapperMapper);
 		}
 
 	}

module/spring-boot-jdbc/src/main/java/org/springframework/boot/jdbc/autoconfigure/JdbcConnectionDetailsBeanPostProcessor.java

@@ -49,7 +49,7 @@ abstract class JdbcConnectionDetailsBeanPostProcessor<T> implements BeanPostProc
 	@Override
 	@SuppressWarnings("unchecked")
 	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
-		if (this.dataSourceClass.isAssignableFrom(bean.getClass()) && "dataSource".equals(beanName)) {
+		if (this.dataSourceClass.isInstance(bean) && "dataSource".equals(beanName)) {
 			JdbcConnectionDetails connectionDetails = this.connectionDetailsProvider.getObject();
 			if (!(connectionDetails instanceof PropertiesJdbcConnectionDetails)) {
 				return processDataSource((T) bean, connectionDetails);

module/spring-boot-micrometer-tracing/src/main/java/org/springframework/boot/micrometer/tracing/autoconfigure/TracingAndMeterObservationHandlerGroup.java

@@ -47,7 +47,7 @@ class TracingAndMeterObservationHandlerGroup implements ObservationHandlerGroup
 
 	@Override
 	public boolean isMember(ObservationHandler<?> handler) {
-		return MeterObservationHandler.class.isInstance(handler) || TracingObservationHandler.class.isInstance(handler);
+		return handler instanceof MeterObservationHandler || handler instanceof TracingObservationHandler;
 	}
 
 	@Override

module/spring-boot-tomcat/src/main/java/org/springframework/boot/tomcat/autoconfigure/TomcatWebServerFactoryCustomizer.java

@@ -320,7 +320,7 @@ private <T extends ProtocolHandler> void customizeHandler(ConfigurableTomcatWebS
 			Class<T> type, ObjIntConsumer<T> consumer) {
 		factory.addConnectorCustomizers((connector) -> {
 			ProtocolHandler handler = connector.getProtocolHandler();
-			if (type.isAssignableFrom(handler.getClass())) {
+			if (type.isInstance(handler)) {
 				consumer.accept(type.cast(handler), value);
 			}
 		});