使用 RestTemplate 与对象作为数据和 application/x-www-form-urlencoded 内容类型？

Question

我需要通过内容类型为application/x-www-form-urlencoded的RestTemplate发布一个对象（例如不是MultiValueMap ）。 当我尝试这样做时...

HttpHeaders headers = new HttpHeaders();
HttpEntity request;

headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED)

// data is some generic type
request = new HttpEntity<>(data, headers);

// clazz is the Class<T> being returned
restTemplate.exchange(url, method, request, clazz)

...我收到以下错误：

org.springframework.web.client.RestClientException：无法写入请求：找不到适合请求类型 [com.whatever.MyRequestPayload] 和内容类型 [application/x-www-form-urlencoded] 的 HttpMessageConverter

这是我在restTemplate.getMessageConverters()看到的：

为什么我不想提供MultiValueMap ？ 两个原因：

1. 这是用于向多个端点发送请求的通用代码，因此专门为x-www-form-urlencoded添加重载只会使事情复杂化
2. 似乎我不必 - 我只是不知道需要使用哪个 HttpMessageConverter 来支持将对象转换为x-www-form-urlencoded字符串

Answer 1

我最终不得不编写一个自定义 HTTP 消息转换器，它接受任何对象并将其作为 www-form-urlencoded 内容写出到请求正文：

用法

RestTemplate template = new RestTemplate(...);

template.getMessageConverters().add(new ObjectToUrlEncodedConverter(mapper));

ObjectToUrlEncodedConverter

import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.http.converter.HttpMessageNotWritableException;
import sun.reflect.generics.reflectiveObjects.NotImplementedException;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.Collections;
import java.util.List;

public class ObjectToUrlEncodedConverter implements HttpMessageConverter
{
    private static final String Encoding = "UTF-8";

    private final ObjectMapper mapper;

    public ObjectToUrlEncodedConverter(ObjectMapper mapper)
    {
        this.mapper = mapper;
    }

    @Override
    public boolean canRead(Class clazz, MediaType mediaType)
    {
        return false;
    }

    @Override
    public boolean canWrite(Class clazz, MediaType mediaType)
    {
        return getSupportedMediaTypes().contains(mediaType);
    }

    @Override
    public List<MediaType> getSupportedMediaTypes()
    {
        return Collections.singletonList(MediaType.APPLICATION_FORM_URLENCODED);
    }

    @Override
    public Object read(Class clazz, HttpInputMessage inputMessage) throws HttpMessageNotReadableException
    {
        throw new NotImplementedException();
    }

    @Override
    public void write(Object o, MediaType contentType, HttpOutputMessage outputMessage) throws HttpMessageNotWritableException
    {
        if (o != null)
        {
            String body = mapper
                .convertValue(o, UrlEncodedWriter.class)
                .toString();

            try
            {
                outputMessage.getBody().write(body.getBytes(Encoding));
            }
            catch (IOException e)
            {
                // if UTF-8 is not supporter then I give up
            }
        }
    }

    private static class UrlEncodedWriter
    {
        private final StringBuilder out = new StringBuilder();

        @JsonAnySetter
        public void write(String name, Object property) throws UnsupportedEncodingException
        {
            if (out.length() > 0)
            {
                out.append("&");
            }

            out
                .append(URLEncoder.encode(name, Encoding))
                .append("=");

            if (property != null)
            {
                out.append(URLEncoder.encode(property.toString(), Encoding));
            }
        }

        @Override
        public String toString()
        {
            return out.toString();
        }
    }
}

Answer 2

您是否尝试过将MappingJackson2HttpMessageConverter添加到RestTemplate

restTemplate.getMessageConverters().add(getMappingJackson2HttpMessageConverter());

public MappingJackson2HttpMessageConverter getMappingJackson2HttpMessageConverter() {
    MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter = new MappingJackson2HttpMessageConverter();
    mappingJackson2HttpMessageConverter.setSupportedMediaTypes(Collections.singletonList(MediaType.APPLICATION_FORM_URLENCODED));
    return mappingJackson2HttpMessageConverter;
}

Answer 3

您可以尝试使用https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/http/converter/FormHttpMessageConverter.html

RestTemplate template = new RestTemplate(...);
template.getMessageConverters().add(new org.springframework.http.converter.FormHttpMessageConverter.FormHttpMessageConverter());

Answer 4

如果您使用的是WebMvcConfigurerAdapter那么您可能会遇到此类错误。 此外 WebMvcConfigurerAdapter 已从 Spring 5.xx 弃用尝试使用WebMvcConfigurer 。 完成后，您将必须覆盖：

@Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {}

Answer 5

您可以将 FormHttpMessageConverter 用于内容类型“application/x-www-form-urlencoded”，如下所示，并在 RestTemplate post 方法中为主体发送数据作为 MultiValueMap<String, String>

<bean id="restTemplate" class="org.springframework.web.client.RestTemplate" lazy-init="true">
    <constructor-arg name="requestFactory" ref="bufferingClientHttpRequestFactory" />
    <property name="errorHandler" ref="responeErrorHandler" />
    <property name="messageConverters">
    <list>
        <bean class="org.springframework.http.converter.FormHttpMessageConverter" />
        <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter"/>
    </list>
</property>
</bean>

Java 配置版本

@Bean
public RestTemplate restTemplate() {
    RestTemplate restTemplate = new RestTemplate();          
    restTemplate.getMessageConverters().add(new FormHttpMessageConverter());
    restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
    return restTemplate 
}