Consistent object type exposure for JSON rendering (workaround for Gson)

Issue: SPR-16461

Author: jhoeller

spring-web/src/main/java/org/springframework/http/converter/AbstractGenericHttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -87,21 +87,16 @@ public final void write(final T t, @Nullable final Type type, @Nullable MediaTyp
 
 		if (outputMessage instanceof StreamingHttpOutputMessage) {
 			StreamingHttpOutputMessage streamingOutputMessage = (StreamingHttpOutputMessage) outputMessage;
-			streamingOutputMessage.setBody(new StreamingHttpOutputMessage.Body() {
+			streamingOutputMessage.setBody(outputStream -> writeInternal(t, type, new HttpOutputMessage() {
 				@Override
-				public void writeTo(final OutputStream outputStream) throws IOException {
-					writeInternal(t, type, new HttpOutputMessage() {
-						@Override
-						public OutputStream getBody() throws IOException {
-							return outputStream;
-						}
-						@Override
-						public HttpHeaders getHeaders() {
-							return headers;
-						}
-					});
+				public OutputStream getBody() {
+					return outputStream;
 				}
-			});
+				@Override
+				public HttpHeaders getHeaders() {
+					return headers;
+				}
+			}));
 		}
 		else {
 			writeInternal(t, type, outputMessage);

spring-web/src/main/java/org/springframework/http/converter/json/GsonHttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -18,6 +18,7 @@
 
 import java.io.Reader;
 import java.io.Writer;
+import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 
 import com.google.gson.Gson;
@@ -34,7 +35,7 @@
  * By default, it supports {@code application/json} and {@code application/*+json} with
  * {@code UTF-8} character set.
  *
- * <p>Tested against Gson 2.6; compatible with Gson 2.0 and higher.
+ * <p>Tested against Gson 2.8; compatible with Gson 2.0 and higher.
  *
  * @author Roy Clarkson
  * @author Juergen Hoeller
@@ -93,7 +94,12 @@ protected Object readInternal(Type resolvedType, Reader reader) throws Exception
 
 	@Override
 	protected void writeInternal(Object o, @Nullable Type type, Writer writer) throws Exception {
-		if (type != null) {
+		// In Gson, toJson with a type argument will exclusively use that given type,
+		// ignoring the actual type of the object... which might be more specific,
+		// e.g. a subclass of the specified type which includes additional fields.
+		// As a consequence, we're only passing in parameterized type declarations
+		// which might contain extra generics that the object instance doesn't retain.
+		if (type instanceof ParameterizedType) {
 			getGson().toJson(o, type, writer);
 		}
 		else {

spring-web/src/main/java/org/springframework/http/converter/json/JsonbHttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -18,6 +18,7 @@
 
 import java.io.Reader;
 import java.io.Writer;
+import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import javax.json.bind.Jsonb;
 import javax.json.bind.JsonbBuilder;
@@ -100,7 +101,7 @@ protected Object readInternal(Type resolvedType, Reader reader) throws Exception
 
 	@Override
 	protected void writeInternal(Object o, @Nullable Type type, Writer writer) throws Exception {
-		if (type != null) {
+		if (type instanceof ParameterizedType) {
 			getJsonb().toJson(o, type, writer);
 		}
 		else {

spring-web/src/test/java/org/springframework/http/converter/json/GsonHttpMessageConverterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -27,6 +27,7 @@
 import java.util.Map;
 
 import org.junit.Test;
+import org.skyscreamer.jsonassert.JSONAssert;
 
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.http.MediaType;
@@ -40,6 +41,7 @@
  * Gson 2.x converter tests.
  *
  * @author Roy Clarkson
+ * @author Juergen Hoeller
  */
 public class GsonHttpMessageConverterTests {
 
@@ -129,6 +131,29 @@ public void write() throws IOException {
 				outputMessage.getHeaders().getContentType());
 	}
 
+	@Test
+	public void writeWithBaseType() throws IOException {
+		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
+		MyBean body = new MyBean();
+		body.setString("Foo");
+		body.setNumber(42);
+		body.setFraction(42F);
+		body.setArray(new String[] {"Foo", "Bar"});
+		body.setBool(true);
+		body.setBytes(new byte[] {0x1, 0x2});
+		this.converter.write(body, MyBase.class, null, outputMessage);
+		Charset utf8 = StandardCharsets.UTF_8;
+		String result = outputMessage.getBodyAsString(utf8);
+		assertTrue(result.contains("\"string\":\"Foo\""));
+		assertTrue(result.contains("\"number\":42"));
+		assertTrue(result.contains("fraction\":42.0"));
+		assertTrue(result.contains("\"array\":[\"Foo\",\"Bar\"]"));
+		assertTrue(result.contains("\"bool\":true"));
+		assertTrue(result.contains("\"bytes\":[1,2]"));
+		assertEquals("Invalid content-type", new MediaType("application", "json", utf8),
+				outputMessage.getHeaders().getContentType());
+	}
+
 	@Test
 	public void writeUTF16() throws IOException {
 		MediaType contentType = new MediaType("application", "json", StandardCharsets.UTF_16BE);
@@ -149,7 +174,7 @@ public void readInvalidJson() throws IOException {
 
 	@Test
 	@SuppressWarnings("unchecked")
-	public void readGenerics() throws Exception {
+	public void readAndWriteGenerics() throws Exception {
 		Field beansList = ListHolder.class.getField("listField");
 
 		String body = "[{\"bytes\":[1,2],\"array\":[\"Foo\",\"Bar\"]," +
@@ -164,14 +189,18 @@ public void readGenerics() throws Exception {
 		assertEquals("Foo", result.getString());
 		assertEquals(42, result.getNumber());
 		assertEquals(42F, result.getFraction(), 0F);
-		assertArrayEquals(new String[] { "Foo", "Bar" }, result.getArray());
+		assertArrayEquals(new String[] {"Foo", "Bar"}, result.getArray());
 		assertTrue(result.isBool());
-		assertArrayEquals(new byte[] { 0x1, 0x2 }, result.getBytes());
+		assertArrayEquals(new byte[] {0x1, 0x2}, result.getBytes());
+
+		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
+		converter.write(results, genericType, new MediaType("application", "json"), outputMessage);
+		JSONAssert.assertEquals(body, outputMessage.getBodyAsString(StandardCharsets.UTF_8), true);
 	}
 
 	@Test
 	@SuppressWarnings("unchecked")
-	public void readParameterizedType() throws Exception {
+	public void readAndWriteParameterizedType() throws Exception {
 		ParameterizedTypeReference<List<MyBean>> beansList = new ParameterizedTypeReference<List<MyBean>>() {
 		};
 
@@ -186,32 +215,74 @@ public void readParameterizedType() throws Exception {
 		assertEquals("Foo", result.getString());
 		assertEquals(42, result.getNumber());
 		assertEquals(42F, result.getFraction(), 0F);
-		assertArrayEquals(new String[] { "Foo", "Bar" }, result.getArray());
+		assertArrayEquals(new String[] {"Foo", "Bar"}, result.getArray());
 		assertTrue(result.isBool());
 		assertArrayEquals(new byte[] {0x1, 0x2}, result.getBytes());
+
+		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
+		converter.write(results, beansList.getType(), new MediaType("application", "json"), outputMessage);
+		JSONAssert.assertEquals(body, outputMessage.getBodyAsString(StandardCharsets.UTF_8), true);
 	}
 
 	@Test
-	public void prefixJson() throws Exception {
+	@SuppressWarnings("unchecked")
+	public void writeParameterizedBaseType() throws Exception {
+		ParameterizedTypeReference<List<MyBean>> beansList = new ParameterizedTypeReference<List<MyBean>>() {};
+		ParameterizedTypeReference<List<MyBase>> baseList = new ParameterizedTypeReference<List<MyBase>>() {};
+
+		String body = "[{\"bytes\":[1,2],\"array\":[\"Foo\",\"Bar\"]," +
+				"\"number\":42,\"string\":\"Foo\",\"bool\":true,\"fraction\":42.0}]";
+		MockHttpInputMessage inputMessage = new MockHttpInputMessage(body.getBytes(StandardCharsets.UTF_8));
+		inputMessage.getHeaders().setContentType(new MediaType("application", "json"));
+
+		List<MyBean> results = (List<MyBean>) converter.read(beansList.getType(), null, inputMessage);
+		assertEquals(1, results.size());
+		MyBean result = results.get(0);
+		assertEquals("Foo", result.getString());
+		assertEquals(42, result.getNumber());
+		assertEquals(42F, result.getFraction(), 0F);
+		assertArrayEquals(new String[] {"Foo", "Bar"}, result.getArray());
+		assertTrue(result.isBool());
+		assertArrayEquals(new byte[] {0x1, 0x2}, result.getBytes());
+
+		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
+		converter.write(results, baseList.getType(), new MediaType("application", "json"), outputMessage);
+		JSONAssert.assertEquals(body, outputMessage.getBodyAsString(StandardCharsets.UTF_8), true);
+	}
+
+	@Test
+	public void prefixJson() throws IOException {
 		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
 		this.converter.setPrefixJson(true);
 		this.converter.writeInternal("foo", null, outputMessage);
 		assertEquals(")]}', \"foo\"", outputMessage.getBodyAsString(StandardCharsets.UTF_8));
 	}
 
 	@Test
-	public void prefixJsonCustom() throws Exception {
+	public void prefixJsonCustom() throws IOException {
 		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
 		this.converter.setJsonPrefix(")))");
 		this.converter.writeInternal("foo", null, outputMessage);
 		assertEquals(")))\"foo\"", outputMessage.getBodyAsString(StandardCharsets.UTF_8));
 	}
 
 
-	public static class MyBean {
+	public static class MyBase {
 
 		private String string;
 
+		public String getString() {
+			return string;
+		}
+
+		public void setString(String string) {
+			this.string = string;
+		}
+	}
+
+
+	public static class MyBean extends MyBase {
+
 		private int number;
 
 		private float fraction;
@@ -222,30 +293,6 @@ public static class MyBean {
 
 		private byte[] bytes;
 
-		public byte[] getBytes() {
-			return bytes;
-		}
-
-		public void setBytes(byte[] bytes) {
-			this.bytes = bytes;
-		}
-
-		public boolean isBool() {
-			return bool;
-		}
-
-		public void setBool(boolean bool) {
-			this.bool = bool;
-		}
-
-		public String getString() {
-			return string;
-		}
-
-		public void setString(String string) {
-			this.string = string;
-		}
-
 		public int getNumber() {
 			return number;
 		}
@@ -269,6 +316,22 @@ public String[] getArray() {
 		public void setArray(String[] array) {
 			this.array = array;
 		}
+
+		public boolean isBool() {
+			return bool;
+		}
+
+		public void setBool(boolean bool) {
+			this.bool = bool;
+		}
+
+		public byte[] getBytes() {
+			return bytes;
+		}
+
+		public void setBytes(byte[] bytes) {
+			this.bytes = bytes;
+		}
 	}