SpringBoot使用RestTemplate消费REST服务的几个问题记录
我们可以通过Spring Boot快速开发REST接口,同时也可能需要在实现接口的过程中,通过Spring Boot调用内外部REST接口完成业务逻辑。
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在Spring Boot中,调用REST Api常见的一般主要有两种方式,通过自带的RestTemplate或者自己开发http客户端工具实现服务调用。
RestTemplate基本功能非常强大,不过某些特殊场景,我们可能还是更习惯用自己封装的工具类,比如上传文件至分布式文件系统、处理带证书的https请求等。
本文以RestTemplate来举例,记录几个使用RestTemplate调用接口过程中发现的问题和解决方案。
一、RestTemplate简介
1、什么是RestTemplate
我们自己封装的HttpClient,通常都会有一些模板代码,比如建立连接,构造请求头和请求体,然后根据响应,解析响应信息,最后关闭连接。
RestTemplate是Spring中对HttpClient的再次封装,简化了发起HTTP请求以及处理响应的过程,抽象层级更高,减少消费者的模板代码,使冗余代码更少。
其实仔细想想Spring Boot下的很多XXXTemplate类,它们也提供各种模板方法,只不过抽象的层次更高,隐藏了更多细节而已。
顺便提一下,Spring Cloud有一个声明式服务调用Feign,是基于Netflix Feign实现的,整合了Spring Cloud Ribbon与 Spring Cloud Hystrix,并且实现了声明式的Web服务客户端定义方式。
本质上Feign是在RestTemplate的基础上对其再次封装,由它来帮助我们定义和实现依赖服务接口的定义。
2、RestTemplate常见方法
常见的REST服务有很多种请求方式,如GET,POST,PUT,DELETE,HEAD,OPTIONS等。RestTemplate实现了最常见的方式,用的最多的就是Get和Post了,调用API可参考源码,这里列举几个方法定义(GET、POST、DELETE):
methods
publicT getForObject(String url, Class responseType, Object... uriVariables) public ResponseEntity getForEntity(String url, Class responseType, Object... uriVariables) public T postForObject(String url, @Nullable Object request, Class responseType,Object... uriVariables) public ResponseEntity postForEntity(String url, @Nullable Object request,Class responseType, Object... uriVariables) public void delete(String url, Object... uriVariables) public void delete(URI url)
同时要注意两个较为“灵活”的方法 exchange 和 execute 。
RestTemplate暴露的exchange与其它接口的不同:
(1)允许调用者指定HTTP请求的方法(GET,POST,DELETE等)
(2)可以在请求中增加body以及头信息,其内容通过参数‘HttpEntity<?>requestEntity'描述
(3)exchange支持‘含参数的类型'(即泛型类)作为返回类型,该特性通过‘ParameterizedTypeReference
RestTemplate所有的GET,POST等等方法,最终调用的都是execute方法。excute方法的内部实现是将String格式的URI转成了java.net.URI,之后调用了doExecute方法,doExecute方法的实现如下:
doExecute
/** * Execute the given method on the provided URI. *The {@link ClientHttpRequest} is processed using the {@link RequestCallback}; * the response with the {@link ResponseExtractor}. * @param url the fully-expanded URL to connect to * @param method the HTTP method to execute (GET, POST, etc.) * @param requestCallback object that prepares the request (can be {@code null}) * @param responseExtractor object that extracts the return value from the response (can be {@code null}) * @return an arbitrary object, as returned by the {@link ResponseExtractor} */ @Nullable protected
T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback, @Nullable ResponseExtractor responseExtractor) throws RestClientException { Assert.notNull(url, "'url' must not be null"); Assert.notNull(method, "'method' must not be null"); ClientHttpResponse response = null; try { ClientHttpRequest request = createRequest(url, method); if (requestCallback != null) { requestCallback.doWithRequest(request); } response = request.execute(); handleResponse(url, method, response); if (responseExtractor != null) { return responseExtractor.extractData(response); } else { return null; } } catch (IOException ex) { String resource = url.toString(); String query = url.getRawQuery(); resource = (query != null ? resource.substring(0, resource.indexOf('?')) : resource); throw new ResourceAccessException("I/O error on " + method.name() + " request for \"" + resource + "\": " + ex.getMessage(), ex); } finally { if (response != null) { response.close(); } } }
doExecute方法封装了模板方法,比如创建连接、处理请求和应答,关闭连接等。
多数人看到这里,估计都会觉得封装一个RestClient不过如此吧?
3、简单调用
以一个POST调用为例:
GoodsServiceClient
package com.power.demo.restclient; import com.power.demo.common.AppConst; import com.power.demo.restclient.clientrequest.ClientGetGoodsByGoodsIdRequest; import com.power.demo.restclient.clientresponse.ClientGetGoodsByGoodsIdResponse; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Value; import org.springframework.stereotype.Component; import org.springframework.web.client.RestTemplate; /** * 商品REST接口客户端 (demo测试用) **/ @Component public class GoodsServiceClient { //服务消费者调用的接口URL 形如:http://localhost:9090 @Value("${spring.power.serviceurl}") private String _serviceUrl; @Autowired private RestTemplate restTemplate; public ClientGetGoodsByGoodsIdResponse getGoodsByGoodsId(ClientGetGoodsByGoodsIdRequest request) { String svcUrl = getGoodsSvcUrl() + "/getinfobyid"; ClientGetGoodsByGoodsIdResponse response = null; try { response = restTemplate.postForObject(svcUrl, request, ClientGetGoodsByGoodsIdResponse.class); } catch (Exception e) { e.printStackTrace(); response = new ClientGetGoodsByGoodsIdResponse(); response.setCode(AppConst.FAIL); response.setMessage(e.toString()); } return response; } private String getGoodsSvcUrl() { String url = ""; if (_serviceUrl == null) { _serviceUrl = ""; } if (_serviceUrl.length() == 0) { return url; } if (_serviceUrl.substring(_serviceUrl.length() - 1, _serviceUrl.length()) == "/") { url = String.format("%sapi/v1/goods", _serviceUrl); } else { url = String.format("%s/api/v1/goods", _serviceUrl); } return url; } }
demo里直接RestTemplate.postForObject方法调用,反序列化实体转换这些RestTemplate内部封装搞定。
二、问题汇总
1、no suitable HttpMessageConverter found for request type异常
这个问题通常会出现在postForObject中传入对象进行调用的时候。
分析RestTemplate源码,在HttpEntityRequestCallback类的doWithRequest方法中,如果 messageConverters (这个字段后面会继续提及)列表字段循环处理的过程中没有满足return跳出的逻辑(也就是没有匹配的HttpMessageConverter),则抛出上述异常:
HttpEntityRequestCallback.doWithRequest
@Override @SuppressWarnings("unchecked") public void doWithRequest(ClientHttpRequest httpRequest) throws IOException { super.doWithRequest(httpRequest); Object requestBody = this.requestEntity.getBody(); if (requestBody == null) { HttpHeaders httpHeaders = httpRequest.getHeaders(); HttpHeaders requestHeaders = this.requestEntity.getHeaders(); if (!requestHeaders.isEmpty()) { for (Map.Entry> entry : requestHeaders.entrySet()) { httpHeaders.put(entry.getKey(), new LinkedList<>(entry.getValue())); } } if (httpHeaders.getContentLength() < 0) { httpHeaders.setContentLength(0L); } } else { Class<?> requestBodyClass = requestBody.getClass(); Type requestBodyType = (this.requestEntity instanceof RequestEntity ? ((RequestEntity<?>)this.requestEntity).getType() : requestBodyClass); HttpHeaders httpHeaders = httpRequest.getHeaders(); HttpHeaders requestHeaders = this.requestEntity.getHeaders(); MediaType requestContentType = requestHeaders.getContentType(); for (HttpMessageConverter<?> messageConverter : getMessageConverters()) { if (messageConverter instanceof GenericHttpMessageConverter) { GenericHttpMessageConverter
最简单的解决方案是,可以通过包装http请求头,并将请求对象序列化成字符串的形式传参,参考示例代码如下:
postForObject
/* * Post请求调用 * */ public static String postForObject(RestTemplate restTemplate, String url, Object params) { HttpHeaders headers = new HttpHeaders(); MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8"); headers.setContentType(type); headers.add("Accept", MediaType.APPLICATION_JSON.toString()); String json = SerializeUtil.Serialize(params); HttpEntityformEntity = new HttpEntity (json, headers); String result = restTemplate.postForObject(url, formEntity, String.class); return result; }
如果我们还想直接返回对象,直接反序列化返回的字符串即可:
postForObject
/* * Post请求调用 * */ public staticT postForObject(RestTemplate restTemplate, String url, Object params, Class clazz) { T response = null; String respStr = postForObject(restTemplate, url, params); response = SerializeUtil.DeSerialize(respStr, clazz); return response; }
其中,序列化和反序列化工具比较多,常用的比如fastjson、jackson和gson。
2、no suitable HttpMessageConverter found for response type异常
和发起请求发生异常一样,处理应答的时候也会有问题。
StackOverflow上有人问过相同的问题,根本原因是HTTP消息转换器HttpMessageConverter缺少 MIME Type ,也就是说HTTP在把输出结果传送到客户端的时候,客户端必须启动适当的应用程序来处理这个输出文档,这可以通过多种MIME(多功能网际邮件扩充协议)Type来完成。
对于服务端应答,很多HttpMessageConverter默认支持的媒体类型(MIMEType)都不同。StringHttpMessageConverter默认支持的则是MediaType.TEXT_PLAIN,SourceHttpMessageConverter默认支持的则是MediaType.TEXT_XML,FormHttpMessageConverter默认支持的是MediaType.APPLICATION_FORM_URLENCODED和MediaType.MULTIPART_FORM_DATA,在REST服务中,我们用到的最多的还是 MappingJackson2HttpMessageConverter ,这是一个比较通用的转化器(继承自GenericHttpMessageConverter接口),根据分析,它默认支持的MIMEType为MediaType.APPLICATION_JSON:
MappingJackson2HttpMessageConverter
/** * 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")); }
但是有些应用接口默认的应答MIMEType不是application/json,比如我们调用一个外部天气预报接口,如果使用RestTemplate的默认配置,直接返回一个字符串应答是没有问题的:
String url = "http://wthrcdn.etouch.cn/weather_mini?city=上海"; String result = restTemplate.getForObject(url, String.class); ClientWeatherResultVO vo = SerializeUtil.DeSerialize(result, ClientWeatherResultVO.class);
但是,如果我们想直接返回一个实体对象:
String url = "http://wthrcdn.etouch.cn/weather_mini?city=上海"; ClientWeatherResultVO weatherResultVO = restTemplate.getForObject(url, ClientWeatherResultVO.class);
则直接报异常:
Could not extract response: no suitable HttpMessageConverter found for response type [class ]
and content type [application/octet-stream]
很多人碰到过这个问题,首次碰到估计大多都比较懵吧,很多接口都是json或者xml或者plain text格式返回的,什么是application/octet-stream?
查看RestTemplate源代码,一路跟踪下去会发现 HttpMessageConverterExtractor 类的extractData方法有个解析应答及反序列化逻辑,如果不成功,抛出的异常信息和上述一致:
HttpMessageConverterExtractor.extractData
@Override @SuppressWarnings({"unchecked", "rawtypes", "resource"}) public T extractData(ClientHttpResponse response) throws IOException { MessageBodyClientHttpResponseWrapper responseWrapper = new MessageBodyClientHttpResponseWrapper(response); if (!responseWrapper.hasMessageBody() || responseWrapper.hasEmptyMessageBody()) { return null; } MediaType contentType = getContentType(responseWrapper); try { for (HttpMessageConverter<?> messageConverter : this.messageConverters) { if (messageConverter instanceof GenericHttpMessageConverter) { GenericHttpMessageConverter<?> genericMessageConverter = (GenericHttpMessageConverter<?>) messageConverter; if (genericMessageConverter.canRead(this.responseType, null, contentType)) { if (logger.isDebugEnabled()) { logger.debug("Reading [" + this.responseType + "] as \"" + contentType + "\" using [" + messageConverter + "]"); } return (T) genericMessageConverter.read(this.responseType, null, responseWrapper); } } if (this.responseClass != null) { if (messageConverter.canRead(this.responseClass, contentType)) { if (logger.isDebugEnabled()) { logger.debug("Reading [" + this.responseClass.getName() + "] as \"" + contentType + "\" using [" + messageConverter + "]"); } return (T) messageConverter.read((Class) this.responseClass, responseWrapper); } } } } catch (IOException | HttpMessageNotReadableException ex) { throw new RestClientException("Error while extracting response for type [" + this.responseType + "] and content type [" + contentType + "]", ex); } throw new RestClientException("Could not extract response: no suitable HttpMessageConverter found " + "for response type [" + this.responseType + "] and content type [" + contentType + "]"); }
StackOverflow上的解决的示例代码可以接受,但是并不准确,常见的MIMEType都应该加进去,贴一下我认为正确的代码:
RestTemplateConfig
package com.power.demo.restclient.config; import com.fasterxml.jackson.databind.ObjectMapper; import com.google.common.collect.Lists; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.web.client.RestTemplateBuilder; import org.springframework.context.annotation.Bean; import org.springframework.http.MediaType; import org.springframework.http.converter.*; import org.springframework.http.converter.cbor.MappingJackson2CborHttpMessageConverter; import org.springframework.http.converter.feed.AtomFeedHttpMessageConverter; import org.springframework.http.converter.feed.RssChannelHttpMessageConverter; import org.springframework.http.converter.json.GsonHttpMessageConverter; import org.springframework.http.converter.json.JsonbHttpMessageConverter; import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter; import org.springframework.http.converter.smile.MappingJackson2SmileHttpMessageConverter; import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter; import org.springframework.http.converter.xml.Jaxb2RootElementHttpMessageConverter; import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter; import org.springframework.http.converter.xml.SourceHttpMessageConverter; import org.springframework.stereotype.Component; import org.springframework.util.ClassUtils; import org.springframework.web.client.RestTemplate; import java.util.Arrays; import java.util.List; @Component public class RestTemplateConfig { private static final boolean romePresent = ClassUtils.isPresent("com.rometools.rome.feed.WireFeed", RestTemplate .class.getClassLoader()); private static final boolean jaxb2Present = ClassUtils.isPresent("javax.xml.bind.Binder", RestTemplate.class.getClassLoader()); private static final boolean jackson2Present = ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", RestTemplate.class.getClassLoader()) && ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", RestTemplate.class.getClassLoader()); private static final boolean jackson2XmlPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.xml.XmlMapper", RestTemplate.class.getClassLoader()); private static final boolean jackson2SmilePresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.smile.SmileFactory", RestTemplate.class.getClassLoader()); private static final boolean jackson2CborPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.cbor.CBORFactory", RestTemplate.class.getClassLoader()); private static final boolean gsonPresent = ClassUtils.isPresent("com.google.gson.Gson", RestTemplate.class.getClassLoader()); private static final boolean jsonbPresent = ClassUtils.isPresent("javax.json.bind.Jsonb", RestTemplate.class.getClassLoader()); // 启动的时候要注意,由于我们在服务中注入了RestTemplate,所以启动的时候需要实例化该类的一个实例 @Autowired private RestTemplateBuilder builder; @Autowired private ObjectMapper objectMapper; // 使用RestTemplateBuilder来实例化RestTemplate对象,spring默认已经注入了RestTemplateBuilder实例 @Bean public RestTemplate restTemplate() { RestTemplate restTemplate = builder.build(); List> messageConverters = Lists.newArrayList(); MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter(); converter.setObjectMapper(objectMapper); //不加会出现异常 //Could not extract response: no suitable HttpMessageConverter found for response type [class ] MediaType[] mediaTypes = new MediaType[]{ MediaType.APPLICATION_JSON, MediaType.APPLICATION_OCTET_STREAM, MediaType.APPLICATION_JSON_UTF8, MediaType.TEXT_HTML, MediaType.TEXT_PLAIN, MediaType.TEXT_XML, MediaType.APPLICATION_STREAM_JSON, MediaType.APPLICATION_ATOM_XML, MediaType.APPLICATION_FORM_URLENCODED, MediaType.APPLICATION_PDF, }; converter.setSupportedMediaTypes(Arrays.asList(mediaTypes)); //messageConverters.add(converter); if (jackson2Present) { messageConverters.add(converter); } else if (gsonPresent) { messageConverters.add(new GsonHttpMessageConverter()); } else if (jsonbPresent) { messageConverters.add(new JsonbHttpMessageConverter()); } messageConverters.add(new FormHttpMessageConverter()); messageConverters.add(new ByteArrayHttpMessageConverter()); messageConverters.add(new StringHttpMessageConverter()); messageConverters.add(new ResourceHttpMessageConverter(false)); messageConverters.add(new SourceHttpMessageConverter()); messageConverters.add(new AllEncompassingFormHttpMessageConverter()); if (romePresent) { messageConverters.add(new AtomFeedHttpMessageConverter()); messageConverters.add(new RssChannelHttpMessageConverter()); } if (jackson2XmlPresent) { messageConverters.add(new MappingJackson2XmlHttpMessageConverter()); } else if (jaxb2Present) { messageConverters.add(new Jaxb2RootElementHttpMessageConverter()); } if (jackson2SmilePresent) { messageConverters.add(new MappingJackson2SmileHttpMessageConverter()); } if (jackson2CborPresent) { messageConverters.add(new MappingJackson2CborHttpMessageConverter()); } restTemplate.setMessageConverters(messageConverters); return restTemplate; } }
看到上面的代码,再对比一下RestTemplate内部实现,就知道我参考了RestTemplate的源码,有洁癖的人可能会说这一坨代码有点啰嗦,上面那一堆static final的变量和messageConverters填充数据方法,暴露了RestTemplate的实现,如果RestTemplate修改了,这里也要改,非常不友好,而且看上去一点也不OO。
经过分析,RestTemplateBuilder.build()构造了RestTemplate对象,只要将内部MappingJackson2HttpMessageConverter修改一下支持的MediaType即可,RestTemplate的messageConverters字段虽然是private final的,我们依然可以通过反射修改之,改进后的代码如下:
RestTemplateConfig
package com.power.demo.restclient.config; import com.fasterxml.jackson.databind.ObjectMapper; import com.google.common.collect.Lists; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.web.client.RestTemplateBuilder; import org.springframework.context.annotation.Bean; import org.springframework.http.MediaType; import org.springframework.http.converter.HttpMessageConverter; import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter; import org.springframework.stereotype.Component; import org.springframework.web.client.RestTemplate; import java.lang.reflect.Field; import java.util.Arrays; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; @Component public class RestTemplateConfig { // 启动的时候要注意,由于我们在服务中注入了RestTemplate,所以启动的时候需要实例化该类的一个实例 @Autowired private RestTemplateBuilder builder; @Autowired private ObjectMapper objectMapper; // 使用RestTemplateBuilder来实例化RestTemplate对象,spring默认已经注入了RestTemplateBuilder实例 @Bean public RestTemplate restTemplate() { RestTemplate restTemplate = builder.build(); List> messageConverters = Lists.newArrayList(); MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter(); converter.setObjectMapper(objectMapper); //不加可能会出现异常 //Could not extract response: no suitable HttpMessageConverter found for response type [class ] MediaType[] mediaTypes = new MediaType[]{ MediaType.APPLICATION_JSON, MediaType.APPLICATION_OCTET_STREAM, MediaType.TEXT_HTML, MediaType.TEXT_PLAIN, MediaType.TEXT_XML, MediaType.APPLICATION_STREAM_JSON, MediaType.APPLICATION_ATOM_XML, MediaType.APPLICATION_FORM_URLENCODED, MediaType.APPLICATION_JSON_UTF8, MediaType.APPLICATION_PDF, }; converter.setSupportedMediaTypes(Arrays.asList(mediaTypes)); try { //通过反射设置MessageConverters Field field = restTemplate.getClass().getDeclaredField("messageConverters"); field.setAccessible(true); List > orgConverterList = (List >) field.get(restTemplate); Optional > opConverter = orgConverterList.stream() .filter(x -> x.getClass().getName().equalsIgnoreCase(MappingJackson2HttpMessageConverter.class .getName())) .findFirst(); if (opConverter.isPresent() == false) { return restTemplate; } messageConverters.add(converter);//添加MappingJackson2HttpMessageConverter //添加原有的剩余的HttpMessageConverter List > leftConverters = orgConverterList.stream() .filter(x -> x.getClass().getName().equalsIgnoreCase(MappingJackson2HttpMessageConverter.class .getName()) == false) .collect(Collectors.toList()); messageConverters.addAll(leftConverters); System.out.println(String.format("【HttpMessageConverter】原有数量:%s,重新构造后数量:%s" , orgConverterList.size(), messageConverters.size())); } catch (Exception e) { e.printStackTrace(); } restTemplate.setMessageConverters(messageConverters); return restTemplate; } }
除了一个messageConverters字段,看上去我们不再关心RestTemplate那些外部依赖包和内部构造过程,果然干净简洁好维护了很多。
3、乱码问题
这个也是一个非常经典的问题。解决方案非常简单,找到HttpMessageConverter,看看默认支持的Charset。AbstractJackson2HttpMessageConverter是很多HttpMessageConverter的基类,默认编码为UTF-8:
AbstractJackson2HttpMessageConverter
public abstract class AbstractJackson2HttpMessageConverter extends AbstractGenericHttpMessageConverter{ public static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8; }
而StringHttpMessageConverter比较特殊,有人反馈过发生乱码问题由它默认支持的编码 ISO-8859-1 引起:
StringHttpMessageConverter
/** * Implementation of {@link HttpMessageConverter} that can read and write strings. * *By default, this converter supports all media types ({@code }), * and writes with a {@code Content-Type} of {@code text/plain}. This can be overridden * by setting the {@link #setSupportedMediaTypes supportedMediaTypes} property. * * @author Arjen Poutsma * @author Juergen Hoeller * @since 3.0 */ public class StringHttpMessageConverter extends AbstractHttpMessageConverter
{ public static final Charset DEFAULT_CHARSET = StandardCharsets.ISO_8859_1; /** * A default constructor that uses {@code "ISO-8859-1"} as the default charset. * @see #StringHttpMessageConverter(Charset) */ public StringHttpMessageConverter() { this(DEFAULT_CHARSET); } }
如果在使用过程中发生乱码,我们可以通过方法设置HttpMessageConverter支持的编码,常用的有UTF-8、GBK等。
4、反序列化异常
这是开发过程中容易碰到的又一个问题。因为Java的开源框架和工具类非常之多,而且版本更迭频繁,所以经常发生一些意想不到的坑。
以joda time为例,joda time是流行的java时间和日期框架,但是如果你的接口对外暴露joda time的类型,比如DateTime,那么接口调用方(同构和异构系统)可能会碰到序列化难题,反序列化时甚至直接抛出如下异常:
org.springframework.http.converter.HttpMessageConversionException: Type definition error: [simple type, class org.joda.time.Chronology]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.joda.time.Chronology` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
at [Source: (PushbackInputStream);
我在前厂就碰到过,后来为了调用方便,改回直接暴露Java的Date类型。
当然解决的方案不止这一种,可以使用jackson支持自定义类的序列化和反序列化的方式。在精度要求不是很高的系统里,实现简单的DateTime自定义序列化:
DateTimeSerializer
package com.power.demo.util; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.JsonSerializer; import com.fasterxml.jackson.databind.SerializerProvider; import org.joda.time.DateTime; import org.joda.time.format.DateTimeFormat; import org.joda.time.format.DateTimeFormatter; import java.io.IOException; /** * 在默认情况下,jackson会将joda time序列化为较为复杂的形式,不利于阅读,并且对象较大。 ** JodaTime 序列化的时候可以将datetime序列化为字符串,更容易读 **/ public class DateTimeSerializer extends JsonSerializer
{ private static DateTimeFormatter dateFormatter = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss"); @Override public void serialize(DateTime value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException { jgen.writeString(value.toString(dateFormatter)); } }
以及DateTime反序列化:
DatetimeDeserializer
package com.power.demo.util; import com.fasterxml.jackson.core.JsonParser; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.DeserializationContext; import com.fasterxml.jackson.databind.JsonDeserializer; import com.fasterxml.jackson.databind.JsonNode; import org.joda.time.DateTime; import org.joda.time.format.DateTimeFormat; import org.joda.time.format.DateTimeFormatter; import java.io.IOException; /** * JodaTime 反序列化将字符串转化为datetime **/ public class DatetimeDeserializer extends JsonDeserializer{ private static DateTimeFormatter dateFormatter = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss"); @Override public DateTime deserialize(JsonParser jp, DeserializationContext context) throws IOException, JsonProcessingException { JsonNode node = jp.getCodec().readTree(jp); String s = node.asText(); DateTime parse = DateTime.parse(s, dateFormatter); return parse; } }
最后可以在RestTemplateConfig类中对常见调用问题进行汇总处理,可以参考如下:
RestTemplateConfig
package com.power.demo.restclient.config; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.module.SimpleModule; import com.google.common.collect.Lists; import com.power.demo.util.DateTimeSerializer; import com.power.demo.util.DatetimeDeserializer; import org.joda.time.DateTime; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.web.client.RestTemplateBuilder; import org.springframework.context.annotation.Bean; import org.springframework.http.MediaType; import org.springframework.http.converter.HttpMessageConverter; import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter; import org.springframework.stereotype.Component; import org.springframework.web.client.RestTemplate; import java.lang.reflect.Field; import java.util.Arrays; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; @Component public class RestTemplateConfig { // 启动的时候要注意,由于我们在服务中注入了RestTemplate,所以启动的时候需要实例化该类的一个实例 @Autowired private RestTemplateBuilder builder; @Autowired private ObjectMapper objectMapper; // 使用RestTemplateBuilder来实例化RestTemplate对象,spring默认已经注入了RestTemplateBuilder实例 @Bean public RestTemplate restTemplate() { RestTemplate restTemplate = builder.build(); //注册model,用于实现jackson joda time序列化和反序列化 SimpleModule module = new SimpleModule(); module.addSerializer(DateTime.class, new DateTimeSerializer()); module.addDeserializer(DateTime.class, new DatetimeDeserializer()); objectMapper.registerModule(module); List> messageConverters = Lists.newArrayList(); MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter(); converter.setObjectMapper(objectMapper); //不加会出现异常 //Could not extract response: no suitable HttpMessageConverter found for response type [class ] MediaType[] mediaTypes = new MediaType[]{ MediaType.APPLICATION_JSON, MediaType.APPLICATION_OCTET_STREAM, MediaType.TEXT_HTML, MediaType.TEXT_PLAIN, MediaType.TEXT_XML, MediaType.APPLICATION_STREAM_JSON, MediaType.APPLICATION_ATOM_XML, MediaType.APPLICATION_FORM_URLENCODED, MediaType.APPLICATION_JSON_UTF8, MediaType.APPLICATION_PDF, }; converter.setSupportedMediaTypes(Arrays.asList(mediaTypes)); try { //通过反射设置MessageConverters Field field = restTemplate.getClass().getDeclaredField("messageConverters"); field.setAccessible(true); List > orgConverterList = (List >) field.get(restTemplate); Optional > opConverter = orgConverterList.stream() .filter(x -> x.getClass().getName().equalsIgnoreCase(MappingJackson2HttpMessageConverter.class .getName())) .findFirst(); if (opConverter.isPresent() == false) { return restTemplate; } messageConverters.add(converter);//添加MappingJackson2HttpMessageConverter //添加原有的剩余的HttpMessageConverter List > leftConverters = orgConverterList.stream() .filter(x -> x.getClass().getName().equalsIgnoreCase(MappingJackson2HttpMessageConverter.class .getName()) == false) .collect(Collectors.toList()); messageConverters.addAll(leftConverters); System.out.println(String.format("【HttpMessageConverter】原有数量:%s,重新构造后数量:%s" , orgConverterList.size(), messageConverters.size())); } catch (Exception e) { e.printStackTrace(); } restTemplate.setMessageConverters(messageConverters); return restTemplate; } }
目前良好地解决了RestTemplate常用调用问题,而且不需要你写RestTemplate帮助工具类了。
上面列举的这些常见问题,其实.NET下面也有,有兴趣大家可以搜索一下微软的HttpClient常见使用问题,用过的人都深有体会。更不用提 RestSharp 这个开源类库,几年前用的过程中发现了非常多的Bug,到现在还有一个反序列化数组的问题困扰着我们,我只好自己造个简单轮子特殊处理,给我最深刻的经验就是,很多看上去简单的功能,真的碰到了依然会花掉不少的时间去排查和解决,甚至要翻看源码。所以,我们写代码要认识到,越是通用的工具,越需要考虑到特例,可能你需要花80%以上的精力去处理20%的特殊情况,这估计也是满足常见的二八定律吧。
参考:
https://stackoverflow.com/questions/21854369/no-suitable-httpmessageconverter-found-for-response-type
https://stackoverflow.com/questions/40726145/rest-templatecould-not-extract-response-no-suitable-httpmessageconverter-found
https://stackoverflow.com/questions/10579122/resttemplate-no-suitable-httpmessageconverter
http://forum.spring.io/forum/spring-projects/android/126794-no-suitable-httpmessageconverter-found
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持创新互联。
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