Trim whitespace in BasicJsonParser

Previously, whitespace in between the keys and values in the JSON was
not trimmed correctly in BasicJsonParser which lead to it incorrectly
parsing JSON with whitespace between the opening of a list ([) and the
opening of a map ({).

This commit updates the parser to trim unwanted whitespace and adds a
test to AbstractJsonParserTests to verify the whitespace handling
behaviour across all JsonParser implementations.

Closes gh-18911

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/json/BasicJsonParser.java

@@ -49,7 +49,7 @@ public class BasicJsonParser extends AbstractJsonParser {
 
 	private List<Object> parseListInternal(String json) {
 		List<Object> list = new ArrayList<>();
-		json = trimLeadingCharacter(trimTrailingCharacter(json, ']'), '[');
+		json = trimLeadingCharacter(trimTrailingCharacter(json, ']'), '[').trim();
 		for (String value : tokenize(json)) {
 			list.add(parseInternal(value));
 		}
@@ -97,7 +97,7 @@ public class BasicJsonParser extends AbstractJsonParser {
 
 	private Map<String, Object> parseMapInternal(String json) {
 		Map<String, Object> map = new LinkedHashMap<>();
-		json = trimLeadingCharacter(trimTrailingCharacter(json, '}'), '{');
+		json = trimLeadingCharacter(trimTrailingCharacter(json, '}'), '{').trim();
 		for (String pair : tokenize(json)) {
 			String[] values = StringUtils.trimArrayElements(StringUtils.split(pair, ":"));
 			String key = trimLeadingCharacter(trimTrailingCharacter(values[0], '"'), '"');
@@ -151,7 +151,7 @@ public class BasicJsonParser extends AbstractJsonParser {
 			index++;
 		}
 		if (build.length() > 0) {
-			list.add(build.toString());
+			list.add(build.toString().trim());
 		}
 		return list;
 	}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/json/AbstractJsonParserTests.java

@@ -101,6 +101,17 @@ public abstract class AbstractJsonParserTests {
 				.parseMap("{\"foo\":[{\"foo\":\"bar\",\"spam\":1},{\"foo\":\"baz\",\"spam\":2}]}");
 		assertThat(map).hasSize(1);
 		assertThat(((List<Object>) map.get("foo"))).hasSize(2);
+		assertThat(map.get("foo")).asList().allMatch(Map.class::isInstance);
+	}
+
+	@SuppressWarnings("unchecked")
+	@Test
+	public void nestedLeadingAndTrailingWhitespace() {
+		Map<String, Object> map = this.parser.parseMap(
+				" {\"foo\": [ { \"foo\" : \"bar\" , \"spam\" : 1 } , { \"foo\" : \"baz\" , \"spam\" : 2 } ] } ");
+		assertThat(map).hasSize(1);
+		assertThat(((List<Object>) map.get("foo"))).hasSize(2);
+		assertThat(map.get("foo")).asList().allMatch(Map.class::isInstance);
 	}
 
 	@Test