Extract WritableJson from JsonWriter

Make `WritableJson` a top level class rather than a nested class inside
`WritableJson`.

Closes gh-42595

Author: philwebb

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

@@ -25,7 +25,6 @@
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
 
-import org.springframework.boot.json.JsonWriter.WritableJson;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.function.ThrowingConsumer;

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

@@ -16,14 +16,7 @@
 
 package org.springframework.boot.json;
 
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.io.OutputStream;
-import java.io.OutputStreamWriter;
-import java.io.UncheckedIOException;
-import java.io.Writer;
-import java.nio.charset.Charset;
-import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
@@ -37,7 +30,6 @@
 
 import org.springframework.boot.json.JsonValueWriter.Series;
 import org.springframework.boot.json.JsonWriter.Member.Extractor;
-import org.springframework.core.io.WritableResource;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
@@ -159,148 +151,6 @@ static <T> JsonWriter<T> of(Consumer<Members<T>> members) {
 		return (instance, out) -> initializedMembers.write(instance, new JsonValueWriter(out));
 	}
 
-	/**
-	 * JSON content that can be written out.
-	 */
-	@FunctionalInterface
-	interface WritableJson {
-
-		/**
-		 * Write the JSON to the provided {@link Appendable}.
-		 * @param out the {@link Appendable} to receive the JSON
-		 * @throws IOException on IO error
-		 */
-		void to(Appendable out) throws IOException;
-
-		/**
-		 * Write the JSON to a {@link String}.
-		 * @return the JSON string
-		 */
-		default String toJsonString() {
-			try {
-				StringBuilder stringBuilder = new StringBuilder();
-				to(stringBuilder);
-				return stringBuilder.toString();
-			}
-			catch (IOException ex) {
-				throw new UncheckedIOException(ex);
-			}
-		}
-
-		/**
-		 * Write the JSON to a UTF-8 encoded byte array.
-		 * @return the JSON bytes
-		 */
-		default byte[] toByteArray() {
-			return toByteArray(StandardCharsets.UTF_8);
-		}
-
-		/**
-		 * Write the JSON to a byte array.
-		 * @param charset the charset
-		 * @return the JSON bytes
-		 */
-		default byte[] toByteArray(Charset charset) {
-			Assert.notNull(charset, "'charset' must not be null");
-			try (ByteArrayOutputStream out = new ByteArrayOutputStream()) {
-				toWriter(new OutputStreamWriter(out, charset));
-				return out.toByteArray();
-			}
-			catch (IOException ex) {
-				throw new UncheckedIOException(ex);
-			}
-		}
-
-		/**
-		 * Write the JSON to the provided {@link WritableResource} using
-		 * {@link StandardCharsets#UTF_8 UTF8} encoding.
-		 * @param out the {@link OutputStream} to receive the JSON
-		 * @throws IOException on IO error
-		 */
-		default void toResource(WritableResource out) throws IOException {
-			Assert.notNull(out, "'out' must not be null");
-			try (OutputStream outputStream = out.getOutputStream()) {
-				toOutputStream(outputStream);
-			}
-		}
-
-		/**
-		 * Write the JSON to the provided {@link WritableResource} using the given
-		 * {@link Charset}.
-		 * @param out the {@link OutputStream} to receive the JSON
-		 * @param charset the charset to use
-		 * @throws IOException on IO error
-		 */
-		default void toResource(WritableResource out, Charset charset) throws IOException {
-			Assert.notNull(out, "'out' must not be null");
-			Assert.notNull(charset, "'charset' must not be null");
-			try (OutputStream outputStream = out.getOutputStream()) {
-				toOutputStream(outputStream, charset);
-			}
-		}
-
-		/**
-		 * Write the JSON to the provided {@link OutputStream} using
-		 * {@link StandardCharsets#UTF_8 UTF8} encoding. The output stream will not be
-		 * closed.
-		 * @param out the {@link OutputStream} to receive the JSON
-		 * @throws IOException on IO error
-		 * @see #toOutputStream(OutputStream, Charset)
-		 */
-		default void toOutputStream(OutputStream out) throws IOException {
-			toOutputStream(out, StandardCharsets.UTF_8);
-		}
-
-		/**
-		 * Write the JSON to the provided {@link OutputStream} using the given
-		 * {@link Charset}. The output stream will not be closed.
-		 * @param out the {@link OutputStream} to receive the JSON
-		 * @param charset the charset to use
-		 * @throws IOException on IO error
-		 */
-		default void toOutputStream(OutputStream out, Charset charset) throws IOException {
-			Assert.notNull(out, "'out' must not be null");
-			Assert.notNull(charset, "'charset' must not be null");
-			toWriter(new OutputStreamWriter(out, charset));
-		}
-
-		/**
-		 * Write the JSON to the provided {@link Writer}. The writer will be flushed but
-		 * not closed.
-		 * @param out the {@link Writer} to receive the JSON
-		 * @throws IOException on IO error
-		 * @see #toOutputStream(OutputStream, Charset)
-		 */
-		default void toWriter(Writer out) throws IOException {
-			Assert.notNull(out, "'out' must not be null");
-			to(out);
-			out.flush();
-		}
-
-		/**
-		 * Factory method used to create a {@link WritableJson} with a sensible
-		 * {@link Object#toString()} that delegate to {@link WritableJson#toJsonString()}.
-		 * @param writableJson the source {@link WritableJson}
-		 * @return a new {@link WritableJson} with a sensible {@link Object#toString()}.
-		 */
-		static WritableJson of(WritableJson writableJson) {
-			return new WritableJson() {
-
-				@Override
-				public void to(Appendable out) throws IOException {
-					writableJson.to(out);
-				}
-
-				@Override
-				public String toString() {
-					return toJsonString();
-				}
-
-			};
-		}
-
-	}
-
 	/**
 	 * Callback used to configure JSON members. Individual members can be declared using
 	 * the various {@code add(...)} methods. Typically, members are declared with a

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

@@ -0,0 +1,175 @@
+/*
+ * Copyright 2012-2024 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
+ *
+ *      https://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;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.OutputStreamWriter;
+import java.io.UncheckedIOException;
+import java.io.Writer;
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
+
+import org.springframework.core.io.WritableResource;
+import org.springframework.util.Assert;
+
+/**
+ * JSON content that can be written out.
+ *
+ * @author Phillip Webb
+ * @author Moritz Halbritter
+ * @since 3.4.0
+ * @see JsonWriter
+ */
+@FunctionalInterface
+public interface WritableJson {
+
+	/**
+	 * Write the JSON to the provided {@link Appendable}.
+	 * @param out the {@link Appendable} to receive the JSON
+	 * @throws IOException on IO error
+	 */
+	void to(Appendable out) throws IOException;
+
+	/**
+	 * Write the JSON to a {@link String}.
+	 * @return the JSON string
+	 */
+	default String toJsonString() {
+		try {
+			StringBuilder stringBuilder = new StringBuilder();
+			to(stringBuilder);
+			return stringBuilder.toString();
+		}
+		catch (IOException ex) {
+			throw new UncheckedIOException(ex);
+		}
+	}
+
+	/**
+	 * Write the JSON to a UTF-8 encoded byte array.
+	 * @return the JSON bytes
+	 */
+	default byte[] toByteArray() {
+		return toByteArray(StandardCharsets.UTF_8);
+	}
+
+	/**
+	 * Write the JSON to a byte array.
+	 * @param charset the charset
+	 * @return the JSON bytes
+	 */
+	default byte[] toByteArray(Charset charset) {
+		Assert.notNull(charset, "'charset' must not be null");
+		try (ByteArrayOutputStream out = new ByteArrayOutputStream()) {
+			toWriter(new OutputStreamWriter(out, charset));
+			return out.toByteArray();
+		}
+		catch (IOException ex) {
+			throw new UncheckedIOException(ex);
+		}
+	}
+
+	/**
+	 * Write the JSON to the provided {@link WritableResource} using
+	 * {@link StandardCharsets#UTF_8 UTF8} encoding.
+	 * @param out the {@link OutputStream} to receive the JSON
+	 * @throws IOException on IO error
+	 */
+	default void toResource(WritableResource out) throws IOException {
+		Assert.notNull(out, "'out' must not be null");
+		try (OutputStream outputStream = out.getOutputStream()) {
+			toOutputStream(outputStream);
+		}
+	}
+
+	/**
+	 * Write the JSON to the provided {@link WritableResource} using the given
+	 * {@link Charset}.
+	 * @param out the {@link OutputStream} to receive the JSON
+	 * @param charset the charset to use
+	 * @throws IOException on IO error
+	 */
+	default void toResource(WritableResource out, Charset charset) throws IOException {
+		Assert.notNull(out, "'out' must not be null");
+		Assert.notNull(charset, "'charset' must not be null");
+		try (OutputStream outputStream = out.getOutputStream()) {
+			toOutputStream(outputStream, charset);
+		}
+	}
+
+	/**
+	 * Write the JSON to the provided {@link OutputStream} using
+	 * {@link StandardCharsets#UTF_8 UTF8} encoding. The output stream will not be closed.
+	 * @param out the {@link OutputStream} to receive the JSON
+	 * @throws IOException on IO error
+	 * @see #toOutputStream(OutputStream, Charset)
+	 */
+	default void toOutputStream(OutputStream out) throws IOException {
+		toOutputStream(out, StandardCharsets.UTF_8);
+	}
+
+	/**
+	 * Write the JSON to the provided {@link OutputStream} using the given
+	 * {@link Charset}. The output stream will not be closed.
+	 * @param out the {@link OutputStream} to receive the JSON
+	 * @param charset the charset to use
+	 * @throws IOException on IO error
+	 */
+	default void toOutputStream(OutputStream out, Charset charset) throws IOException {
+		Assert.notNull(out, "'out' must not be null");
+		Assert.notNull(charset, "'charset' must not be null");
+		toWriter(new OutputStreamWriter(out, charset));
+	}
+
+	/**
+	 * Write the JSON to the provided {@link Writer}. The writer will be flushed but not
+	 * closed.
+	 * @param out the {@link Writer} to receive the JSON
+	 * @throws IOException on IO error
+	 * @see #toOutputStream(OutputStream, Charset)
+	 */
+	default void toWriter(Writer out) throws IOException {
+		Assert.notNull(out, "'out' must not be null");
+		to(out);
+		out.flush();
+	}
+
+	/**
+	 * Factory method used to create a {@link WritableJson} with a sensible
+	 * {@link Object#toString()} that delegate to {@link WritableJson#toJsonString()}.
+	 * @param writableJson the source {@link WritableJson}
+	 * @return a new {@link WritableJson} with a sensible {@link Object#toString()}.
+	 */
+	static WritableJson of(WritableJson writableJson) {
+		return new WritableJson() {
+
+			@Override
+			public void to(Appendable out) throws IOException {
+				writableJson.to(out);
+			}
+
+			@Override
+			public String toString() {
+				return toJsonString();
+			}
+
+		};
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/GraylogExtendedLogFormatStructuredLogFormatter.java

@@ -33,7 +33,7 @@
 
 import org.springframework.boot.json.JsonWriter;
 import org.springframework.boot.json.JsonWriter.Members;
-import org.springframework.boot.json.JsonWriter.WritableJson;
+import org.springframework.boot.json.WritableJson;
 import org.springframework.boot.logging.structured.CommonStructuredLogFormat;
 import org.springframework.boot.logging.structured.GraylogExtendedLogFormatService;
 import org.springframework.boot.logging.structured.JsonWriterStructuredLogFormatter;

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/StructuredMessage.java

@@ -21,7 +21,7 @@
 import org.apache.logging.log4j.message.Message;
 import org.apache.logging.log4j.util.MultiFormatStringBuilderFormattable;
 
-import org.springframework.boot.json.JsonWriter.WritableJson;
+import org.springframework.boot.json.WritableJson;
 
 /**
  * Helper used to adapt {@link Message} for structured writing.

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/GraylogExtendedLogFormatStructuredLogFormatter.java

@@ -33,7 +33,7 @@
 
 import org.springframework.boot.json.JsonWriter;
 import org.springframework.boot.json.JsonWriter.Members;
-import org.springframework.boot.json.JsonWriter.WritableJson;
+import org.springframework.boot.json.WritableJson;
 import org.springframework.boot.logging.structured.CommonStructuredLogFormat;
 import org.springframework.boot.logging.structured.GraylogExtendedLogFormatService;
 import org.springframework.boot.logging.structured.JsonWriterStructuredLogFormatter;