使用带有对象的RestTemplate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)。当我试着这么做的时候...

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)

...我得到以下错误：

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

以下是我在resttemplate.getMessageConverters()中看到的内容：

为什么我不想提供multivalueMap？原因有二：

1. 这是用于向多个endpoint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. 似乎没有必要--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

最后，我不得不编写一个自定义HTTP消息转换器，该转换器接收任何对象，并将其作为www.form-urlencoded内容写入请求正文：

RestTemplate template = new RestTemplate(...);

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

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();
        }
    }
}