RestTemplate请求：Could not extract response: no suitable HttpMessageConverter found for response type

1、问题描述

使用RestTemplate发请求时出现
Could not extract response: no suitable HttpMessageConverter found for response type.... content type [text/html;charset=UTF-8]
的问题，具体错误如下：

org.springframework.web.client.UnknownContentTypeException: Could not extract response: no suitable HttpMessageConverter found for response type [class com.tyj.study.rest_template.ResponseB] and content type [text/html;charset=UTF-8]
    at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:126) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
    at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:998) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
    at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:981) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:741) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:674) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
    at org.springframework.web.client.RestTemplate.getForEntity(RestTemplate.java:342) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]

2、问题原因

RestTemplate请求不支持content type [text/html;charset=UTF-8]类型

源码

MappingJackson2HttpMessageConverter

package org.springframework.http.converter.json;

import java.io.IOException;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.ObjectMapper;

import org.springframework.http.MediaType;
import org.springframework.lang.Nullable;

/**
 * Implementation of {@link org.springframework.http.converter.HttpMessageConverter} that can read and
 * write JSON using <a href="https://github.com/FasterXML/jackson">Jackson 2.x's</a> {@link ObjectMapper}.
 *
 * <p>This converter can be used to bind to typed beans, or untyped {@code HashMap} instances.
 *
 * <p>By default, this converter supports {@code application/json} and {@code application/*+json}
 * with {@code UTF-8} character set. This can be overridden by setting the
 * {@link #setSupportedMediaTypes supportedMediaTypes} property.
 *
 * <p>The default constructor uses the default configuration provided by {@link Jackson2ObjectMapperBuilder}.
 *
 * <p>Compatible with Jackson 2.9 to 2.12, as of Spring 5.3.
 *
 * @author Arjen Poutsma
 * @author Keith Donald
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @author Sebastien Deleuze
 * @since 3.1.2
 */
public class MappingJackson2HttpMessageConverter extends AbstractJackson2HttpMessageConverter {

	@Nullable
	private String jsonPrefix;


	/**
	 * Construct a new {@link MappingJackson2HttpMessageConverter} using default configuration
	 * provided by {@link Jackson2ObjectMapperBuilder}.
	 */
	public MappingJackson2HttpMessageConverter() {
		this(Jackson2ObjectMapperBuilder.json().build());
	}

	/**
	 * Construct a new {@link MappingJackson2HttpMessageConverter} with a custom {@link ObjectMapper}.
	 * You can use {@link Jackson2ObjectMapperBuilder} to build it easily.
	 * @see Jackson2ObjectMapperBuilder#json()
	 */
	public MappingJackson2HttpMessageConverter(ObjectMapper objectMapper) {
		super(objectMapper, MediaType.APPLICATION_JSON, new MediaType("application", "*+json"));
	}


	/**
	 * Specify a custom prefix to use for this view's JSON output.
	 * Default is none.
	 * @see #setPrefixJson
	 */
	public void setJsonPrefix(String jsonPrefix) {
		this.jsonPrefix = jsonPrefix;
	}

	/**
	 * Indicate whether the JSON output by this view should be prefixed with ")]}', ". Default is false.
	 * <p>Prefixing the JSON string in this manner is used to help prevent JSON Hijacking.
	 * The prefix renders the string syntactically invalid as a script so that it cannot be hijacked.
	 * This prefix should be stripped before parsing the string as JSON.
	 * @see #setJsonPrefix
	 */
	public void setPrefixJson(boolean prefixJson) {
		this.jsonPrefix = (prefixJson ? ")]}', " : null);
	}


	@Override
	protected void writePrefix(JsonGenerator generator, Object object) throws IOException {
		if (this.jsonPrefix != null) {
			generator.writeRaw(this.jsonPrefix);
		}
	}

}

通过51-53行的代码

	public MappingJackson2HttpMessageConverter(ObjectMapper objectMapper) {
		super(objectMapper, MediaType.APPLICATION_JSON, new MediaType("application", "*+json"));
	}

可以看出RestTemplate 实例化过程时 只支持application/json格式

3、解决办法

在实例化RestTemplate时 手动添加text/plan,text/html格式

 @Bean("restTemplate")
    public RestTemplate restTemplate(){
        RestTemplate restTemplate = new RestTemplate();
        MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter = new MappingJackson2HttpMessageConverter();
        mappingJackson2HttpMessageConverter.setSupportedMediaTypes(Arrays.asList(
                MediaType.TEXT_HTML,
                MediaType.TEXT_PLAIN));
        restTemplate.getMessageConverters().add(mappingJackson2HttpMessageConverter);

        return restTemplate;
    }