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/*
 * 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.
 * 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.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.lang.Nullable;
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.
 *
 * 

By default, this converter supports the media type {@code text/plain} only. * This can be overridden through the {@link #setSupportedMediaTypes supportedMediaTypes} * property. * *

A usage example: * *

 * <bean class="org.springframework.http.converter.ObjectToStringHttpMessageConverter">
 *   <constructor-arg>
 *     <bean class="org.springframework.context.support.ConversionServiceFactoryBean"/>
 *   </constructor-arg>
 * </bean>
 * 
* * @author Dmitry Katsubo * @author Rossen Stoyanchev * @since 3.2 */ public class ObjectToStringHttpMessageConverter extends AbstractHttpMessageConverter { private final ConversionService conversionService; private final StringHttpMessageConverter stringHttpMessageConverter; /** * A constructor accepting a {@code ConversionService} to use to convert the * (String) message body to/from the target class type. This constructor uses * {@link StringHttpMessageConverter#DEFAULT_CHARSET} as the default charset. * @param conversionService the conversion service */ public ObjectToStringHttpMessageConverter(ConversionService conversionService) { this(conversionService, StringHttpMessageConverter.DEFAULT_CHARSET); } /** * A constructor accepting a {@code ConversionService} as well as a default charset. * @param conversionService the conversion service * @param defaultCharset the default charset */ public ObjectToStringHttpMessageConverter(ConversionService conversionService, Charset defaultCharset) { super(defaultCharset, MediaType.TEXT_PLAIN); Assert.notNull(conversionService, "ConversionService is required"); this.conversionService = conversionService; this.stringHttpMessageConverter = new StringHttpMessageConverter(defaultCharset); } /** * Delegates to {@link StringHttpMessageConverter#setWriteAcceptCharset(boolean)}. */ public void setWriteAcceptCharset(boolean writeAcceptCharset) { this.stringHttpMessageConverter.setWriteAcceptCharset(writeAcceptCharset); } @Override public boolean canRead(Class clazz, @Nullable MediaType mediaType) { return canRead(mediaType) && this.conversionService.canConvert(String.class, clazz); } @Override public boolean canWrite(Class clazz, @Nullable MediaType mediaType) { return canWrite(mediaType) && this.conversionService.canConvert(clazz, String.class); } @Override protected boolean supports(Class clazz) { // should not be called, since we override canRead/Write throw new UnsupportedOperationException(); } @Override protected Object readInternal(Class clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException { String value = this.stringHttpMessageConverter.readInternal(String.class, inputMessage); Object result = this.conversionService.convert(value, clazz); if (result == null) { throw new HttpMessageNotReadableException( "Unexpected null conversion result for '" + value + "' to " + clazz, inputMessage); } return result; } @Override protected void writeInternal(Object obj, HttpOutputMessage outputMessage) throws IOException { String value = this.conversionService.convert(obj, String.class); if (value != null) { this.stringHttpMessageConverter.writeInternal(value, outputMessage); } } @Override protected Long getContentLength(Object obj, @Nullable MediaType contentType) { String value = this.conversionService.convert(obj, String.class); if (value == null) { return 0L; } return this.stringHttpMessageConverter.getContentLength(value, contentType); } }