Refine `JsonWriter` for structured logging

Add `formatToBytes()` method for use with structured logging.

See gh-41491

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

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.json;
 
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.OutputStreamWriter;
@@ -187,6 +188,29 @@ public interface JsonWriter<T> {
 			}
 		}
 
+		/**
+		 * 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) {
+			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.

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

@@ -480,6 +480,12 @@ public class JsonWriterTests {
 				.withMessage("bad");
 		}
 
+		@Test
+		void toByteArrayReturnsByteArray() {
+			WritableJson writable = (out) -> out.append("{}");
+			assertThat(writable.toByteArray()).isEqualTo("{}".getBytes());
+		}
+
 		@Test
 		void toResourceWritesJson() throws Exception {
 			File file = new File(JsonWriterTests.this.temp, "out.json");