Replace Charset.defaultCharset() with StandardCharsets.UTF_8 in tests

Resolves #4417

(cherry picked from commit 14b6c66)

Author: lsq27

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/builder/FlatFileItemWriterBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 the original author or authors.
+ * Copyright 2016-2023 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.
@@ -19,7 +19,7 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStreamReader;
-import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 
 import org.junit.jupiter.api.Test;
 
@@ -266,7 +266,7 @@ void testFlags() throws Exception {
 
 		WritableResource output = new FileSystemResource(File.createTempFile("foo", "txt"));
 
-		String encoding = Charset.defaultCharset().name();
+		String encoding = StandardCharsets.UTF_8.name();
 
 		FlatFileItemWriter<Foo> writer = new FlatFileItemWriterBuilder<Foo>().name("foo")
 			.resource(output)

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/json/JsonFileItemWriterFunctionalTests.java

@@ -19,7 +19,6 @@
 import java.io.File;
 import java.io.IOException;
 import java.math.BigDecimal;
-import java.nio.charset.Charset;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -334,7 +333,7 @@ private void assertFileEquals(File expected, File actual) throws Exception {
 	}
 
 	private String getContent(File file) throws IOException {
-		return Files.readString(file.toPath(), Charset.defaultCharset());
+		return Files.readString(file.toPath());
 	}
 
 }

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/json/builder/JsonFileItemWriterBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2022 the original author or authors.
+ * Copyright 2018-2023 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.
@@ -17,7 +17,7 @@
 package org.springframework.batch.item.json.builder;
 
 import java.io.File;
-import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 
 import org.junit.jupiter.api.BeforeEach;
@@ -112,7 +112,7 @@ void testJsonFileItemWriterCreationDefaultEncoding() {
 		boolean transactional = true;
 		boolean shouldDeleteIfEmpty = true;
 		boolean shouldDeleteIfExists = true;
-		String encoding = Charset.defaultCharset().name();
+		String encoding = StandardCharsets.UTF_8.name();
 		String lineSeparator = "#";
 		FlatFileHeaderCallback headerCallback = Mockito.mock();
 		FlatFileFooterCallback footerCallback = Mockito.mock();