Add ObjectToStringHttpMessageConverter

This new converter uses StringHttpMessageConverter internally combined
with a ConversionService for converting String content to and from the
target object type.

Issue: SPR-9738

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

@@ -0,0 +1,118 @@
+/*
+ * Copyright 2002-2012 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.http.converter;
+
+import java.io.IOException;
+import java.nio.charset.Charset;
+
+import org.springframework.core.convert.ConversionService;
+import org.springframework.http.HttpInputMessage;
+import org.springframework.http.HttpOutputMessage;
+import org.springframework.http.MediaType;
+import org.springframework.util.Assert;
+
+/**
+ * An {@code HttpMessageConverter} that uses {@link StringHttpMessageConverter}
+ * for reading and writing content and a {@link ConversionService} for converting
+ * the String content to and from the target object type.
+ * <p>
+ * By default, this converter supports the media type {@code text/plain} only.
+ * This can be overridden by setting the
+ * {@link #setSupportedMediaTypes supportedMediaTypes} property.
+ * Example of usage:
+ *
+ * <pre>
+ * &lt;bean class="org.springframework.http.converter.ObjectToStringHttpMessageConverter">
+ *   &lt;constructor-arg>
+ *     &lt;bean class="org.springframework.context.support.ConversionServiceFactoryBean"/>
+ *   &lt;/constructor-arg>
+ * &lt;/bean>
+ * </pre>
+ *
+ * @author <a href="mailto:dmitry.katsubo@gmail.com">Dmitry Katsubo</a>
+ * @author Rossen Stoyanchev
+ * @since 3.2
+ */
+public class ObjectToStringHttpMessageConverter extends AbstractHttpMessageConverter<Object> {
+
+	public static final Charset DEFAULT_CHARSET = Charset.forName("ISO-8859-1");
+
+	private ConversionService conversionService;
+
+	private StringHttpMessageConverter stringHttpMessageConverter;
+
+
+	/**
+	 * A constructor accepting a {@code ConversionService} to use to convert the
+	 * (String) message body to/from the target class type.
+	 * @param conversionService the conversion service
+	 */
+	public ObjectToStringHttpMessageConverter(ConversionService conversionService) {
+		this(conversionService, DEFAULT_CHARSET);
+	}
+
+	public ObjectToStringHttpMessageConverter(ConversionService conversionService, Charset defaultCharset) {
+		super(new MediaType("text", "plain", defaultCharset));
+
+		Assert.notNull(conversionService, "conversionService is required");
+		this.conversionService = conversionService;
+		this.stringHttpMessageConverter = new StringHttpMessageConverter(defaultCharset);
+	}
+
+	/**
+	 * Indicates whether the {@code Accept-Charset} should be written to any outgoing request.
+	 * <p>Default is {@code true}.
+	 */
+	public void setWriteAcceptCharset(boolean writeAcceptCharset) {
+		this.stringHttpMessageConverter.setWriteAcceptCharset(writeAcceptCharset);
+	}
+
+	@Override
+	public boolean canRead(Class<?> clazz, MediaType mediaType) {
+		return this.conversionService.canConvert(String.class, clazz) && canRead(mediaType);
+	}
+
+	@Override
+	public boolean canWrite(Class<?> clazz, MediaType mediaType) {
+		return this.conversionService.canConvert(clazz, String.class) && canWrite(mediaType);
+	}
+
+	@Override
+	protected boolean supports(Class<?> clazz) {
+		// should not be called, since we override canRead/Write
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	protected Object readInternal(Class<? extends Object> clazz, HttpInputMessage inputMessage) throws IOException {
+		String value = this.stringHttpMessageConverter.readInternal(String.class, inputMessage);
+		return this.conversionService.convert(value, clazz);
+	}
+
+	@Override
+	protected void writeInternal(Object obj, HttpOutputMessage outputMessage) throws IOException {
+		String s = this.conversionService.convert(obj, String.class);
+		this.stringHttpMessageConverter.writeInternal(s, outputMessage);
+	}
+
+	@Override
+	protected Long getContentLength(Object obj, MediaType contentType) {
+		String value = this.conversionService.convert(obj, String.class);
+		return this.stringHttpMessageConverter.getContentLength(value, contentType);
+	}
+
+}

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

@@ -76,14 +76,13 @@ public class StringHttpMessageConverter extends AbstractHttpMessageConverter<Str
 		this.writeAcceptCharset = writeAcceptCharset;
 	}
 
-
 	@Override
 	public boolean supports(Class<?> clazz) {
 		return String.class.equals(clazz);
 	}
 
 	@Override
-	protected String readInternal(Class clazz, HttpInputMessage inputMessage) throws IOException {
+	protected String readInternal(Class<? extends String> clazz, HttpInputMessage inputMessage) throws IOException {
 		Charset charset = getContentTypeCharset(inputMessage.getHeaders().getContentType());
 		return FileCopyUtils.copyToString(new InputStreamReader(inputMessage.getBody(), charset));
 	}
@@ -126,5 +125,4 @@ public class StringHttpMessageConverter extends AbstractHttpMessageConverter<Str
 			return this.defaultCharset;
 		}
 	}
-
 }