Insist on using `CollectionUtils.isEmpty()` and `StringUtils.hasLength()`

search `(\w+) != null && !(\1).isEmpty\(\)`

spring-core/src/main/java/org/springframework/util/MultiValueMapAdapter.java

@@ -59,7 +59,7 @@ public class MultiValueMapAdapter<K, V> implements MultiValueMap<K, V>, Serializ
 	@Nullable
 	public V getFirst(K key) {
 		List<V> values = this.targetMap.get(key);
-		return (values != null && !values.isEmpty() ? values.get(0) : null);
+		return (!CollectionUtils.isEmpty(values) ? values.get(0) : null);
 	}
 
 	@Override
@@ -95,7 +95,7 @@ public class MultiValueMapAdapter<K, V> implements MultiValueMap<K, V>, Serializ
 	public Map<K, V> toSingleValueMap() {
 		Map<K, V> singleValueMap = CollectionUtils.newLinkedHashMap(this.targetMap.size());
 		this.targetMap.forEach((key, values) -> {
-			if (values != null && !values.isEmpty()) {
+			if (!CollectionUtils.isEmpty(values)) {
 				singleValueMap.put(key, values.get(0));
 			}
 		});

spring-test/src/test/java/org/springframework/test/web/servlet/samples/client/standalone/MultipartControllerTests.java

@@ -36,6 +36,7 @@ import org.springframework.http.client.MultipartBodyBuilder;
 import org.springframework.stereotype.Controller;
 import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.test.web.servlet.client.MockMvcWebTestClient;
+import org.springframework.util.CollectionUtils;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.PutMapping;
 import org.springframework.web.bind.annotation.RequestParam;
@@ -271,7 +272,7 @@ public class MultipartControllerTests {
 		public String processMultipartFileList(@RequestParam(required = false) List<MultipartFile> file,
 				@RequestPart(required = false) Map<String, String> json) throws IOException {
 
-			if (file != null && !file.isEmpty()) {
+			if (!CollectionUtils.isEmpty(file)) {
 				byte[] content = file.get(0).getBytes();
 				assertThat(file.get(1).getBytes()).isEqualTo(content);
 			}

spring-test/src/test/java/org/springframework/test/web/servlet/samples/standalone/MultipartControllerTests.java

@@ -39,6 +39,7 @@ import org.springframework.mock.web.MockPart;
 import org.springframework.stereotype.Controller;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.request.MockMultipartHttpServletRequestBuilder;
+import org.springframework.util.CollectionUtils;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.PutMapping;
@@ -271,7 +272,7 @@ class MultipartControllerTests {
 		public String processMultipartFileList(@RequestParam(required = false) List<MultipartFile> file,
 				@RequestPart(required = false) Map<String, String> json) throws IOException {
 
-			if (file != null && !file.isEmpty()) {
+			if (!CollectionUtils.isEmpty(file)) {
 				byte[] content = file.get(0).getBytes();
 				assertThat(file.get(1).getBytes()).isEqualTo(content);
 			}

spring-webmvc/src/main/java/org/springframework/web/servlet/support/AbstractFlashMapManager.java

@@ -220,7 +220,7 @@ public abstract class AbstractFlashMapManager implements FlashMapManager {
 
 	@Nullable
 	private String decodeAndNormalizePath(@Nullable String path, HttpServletRequest request) {
-		if (path != null && !path.isEmpty()) {
+		if (StringUtils.hasLength(path)) {
 			path = getUrlPathHelper().decodeRequestString(request, path);
 			if (path.charAt(0) != '/') {
 				String requestUri = getUrlPathHelper().getRequestUri(request);