Polish "refactor spring-boot JSON parser"

Polish JSON parser refactoring and remove some more duplication.

Closes gh-12428

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

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -18,74 +18,49 @@ package org.springframework.boot.json;
 
 import java.util.List;
 import java.util.Map;
-import java.util.Optional;
+import java.util.concurrent.Callable;
 import java.util.function.Function;
 
+import org.springframework.util.ReflectionUtils;
+
 /**
  * Base class for parsers wrapped or implemented in this package.
  *
  * @author Anton Telechev
+ * @author Phillip Webb
  */
 abstract class AbstractJsonParser implements JsonParser {
 
-	/** Start symbol of a JSON map. **/
-	private static final String START_MAP = "{";
-
-	/** Start symbol of a JSON list. **/
-	private static final String START_LIST = "[";
-
-	/**
-	 * Parses the specified JSON string and returns the extracted contents as a Map of
-	 * String to Object.
-	 *
-	 * @param json the JSON string to parse.
-	 * @param parser the parser function.
-	 * @return Map<String, Object> parsed contents
-	 * @throws IllegalArgumentException if the json String cannot be parsed as a
-	 * Map<String, Object>
-	 */
-	Map<String, Object> parseMap(String json,
+	protected final Map<String, Object> parseMap(String json,
 			Function<String, Map<String, Object>> parser) {
-		assert parser != null;
-
-		return trimIfStartsWith(json, START_MAP).map(parser::apply)
-				.orElseThrow(AbstractJsonParser::cannotParseJson);
-	}
-
-	/**
-	 * Parses the specified JSON string and returns the extracted contents as a List of Objects.
-	 *
-	 * @param json the JSON string to parse.
-	 * @param parser the parser function.
-	 * @return List&lt;Object&gt; parsed contents
-	 * @throws IllegalArgumentException if the json String cannot be parsed as a
-	 * List&lt;Object&gt;
-	 */
-	List<Object> parseList(String json, Function<String, List<Object>> parser) {
-		assert parser != null;
-
-		return trimIfStartsWith(json, START_LIST).map(parser::apply)
-				.orElseThrow(AbstractJsonParser::cannotParseJson);
+		return trimParse(json, "{", parser);
 	}
 
-	private static IllegalArgumentException cannotParseJson() {
-		return cannotParseJson(null);
+	protected final List<Object> parseList(String json,
+			Function<String, List<Object>> parser) {
+		return trimParse(json, "[", parser);
 	}
 
-	static IllegalArgumentException cannotParseJson(Exception cause) {
-		return new IllegalArgumentException("Cannot parse JSON", cause);
+	protected final <T> T trimParse(String json, String prefix,
+			Function<String, T> parser) {
+		String trimmed = (json == null ? "" : json.trim());
+		if (trimmed.startsWith(prefix)) {
+			return parser.apply(trimmed);
+		}
+		throw new JsonParseException();
 	}
 
-	private static Optional<String> trimIfStartsWith(String json, String expectedPrefix) {
-		assert expectedPrefix != null;
-
-		if (json != null) {
-			final String trimmed = json.trim();
-			if (trimmed.startsWith(expectedPrefix)) {
-				return Optional.of(trimmed);
+	protected final <T> T tryParse(Callable<T> parser, Class<? extends Exception> check) {
+		try {
+			return parser.call();
+		}
+		catch (Exception ex) {
+			if (check.isAssignableFrom(ex.getClass())) {
+				throw new JsonParseException(ex);
 			}
+			ReflectionUtils.rethrowRuntimeException(ex);
+			throw new IllegalStateException(ex);
 		}
-		return Optional.empty();
 	}
 
 }

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

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.

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

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -28,7 +28,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
  * @author Dave Syer
  * @see JsonParserFactory
  */
-public class JacksonJsonParser implements JsonParser {
+public class JacksonJsonParser extends AbstractJsonParser {
 
 	private static final TypeReference<?> MAP_TYPE = new MapTypeReference();
 
@@ -38,22 +38,14 @@ public class JacksonJsonParser implements JsonParser {
 
 	@Override
 	public Map<String, Object> parseMap(String json) {
-		try {
-			return getObjectMapper().readValue(json, MAP_TYPE);
-		}
-		catch (Exception ex) {
-			throw AbstractJsonParser.cannotParseJson(ex);
-		}
+		return tryParse(() -> getObjectMapper().readValue(json, MAP_TYPE),
+				Exception.class);
 	}
 
 	@Override
 	public List<Object> parseList(String json) {
-		try {
-			return getObjectMapper().readValue(json, LIST_TYPE);
-		}
-		catch (Exception ex) {
-			throw AbstractJsonParser.cannotParseJson(ex);
-		}
+		return tryParse(() -> getObjectMapper().readValue(json, LIST_TYPE),
+				Exception.class);
 	}
 
 	private ObjectMapper getObjectMapper() {

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

+/*
+ * Copyright 2012-2018 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.json;
+
+/**
+ * {@link IllegalArgumentException} thrown when source JSON is invalid.
+ *
+ * @author Anton Telechev
+ * @author Phillip Webb
+ * @since 2.0.1
+ */
+public class JsonParseException extends IllegalArgumentException {
+
+	public JsonParseException() {
+		this(null);
+	}
+
+	public JsonParseException(Throwable cause) {
+		super("Cannot parse JSON", cause);
+	}
+
+}

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

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -35,14 +35,16 @@ public interface JsonParser {
 	 * Parse the specified JSON string into a Map.
 	 * @param json the JSON to parse
 	 * @return the parsed JSON as a map
+	 * @throws JsonParseException if the JSON cannot be parsed
 	 */
-	Map<String, Object> parseMap(String json);
+	Map<String, Object> parseMap(String json) throws JsonParseException;
 
 	/**
 	 * Parse the specified JSON string into a List.
 	 * @param json the JSON to parse
 	 * @return the parsed JSON as a list
+	 * @throws JsonParseException if the JSON cannot be parsed
 	 */
-	List<Object> parseList(String json);
+	List<Object> parseList(String json) throws JsonParseException;
 
 }

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

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -30,28 +30,20 @@ import org.json.simple.parser.ParseException;
  * @since 1.2.0
  * @see JsonParserFactory
  */
-public class JsonSimpleJsonParser implements JsonParser {
+public class JsonSimpleJsonParser extends AbstractJsonParser {
 
 	@Override
 	@SuppressWarnings("unchecked")
 	public Map<String, Object> parseMap(String json) {
-		try {
-			return (Map<String, Object>) new JSONParser().parse(json);
-		}
-		catch (ParseException ex) {
-			throw AbstractJsonParser.cannotParseJson(ex);
-		}
+		return (Map<String, Object>) tryParse(() -> new JSONParser().parse(json),
+				ParseException.class);
 	}
 
 	@Override
 	@SuppressWarnings("unchecked")
 	public List<Object> parseList(String json) {
-		try {
-			return (List<Object>) new JSONParser().parse(json);
-		}
-		catch (ParseException ex) {
-			throw AbstractJsonParser.cannotParseJson(ex);
-		}
+		return (List<Object>) tryParse(() -> new JSONParser().parse(json),
+				ParseException.class);
 	}
 
 }

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

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.