RestTemplate的post请求中文乱码问题

###1.问题重现 需调用的接口如下：

    @RequestMapping(value = "/test", method = RequestMethod.POST)
    public Object createTransGet(HttpServletRequest request, HttpServletResponse response,@RequestBody String text) {
        System.out.println(text);
        return "ok";
    }

RestTemplate调用接口的代码如下：

    @Test
    public void test9() throws UnsupportedEncodingException{
        RestTemplate restTemplate = new RestTemplate();					
        String url = "http://localhost:8080/test";
        JSONObject content = new JSONObject();
        content.put("content","内容内容内容内容内容内容内容");
        String user="用户";
        JSONObject obj = new JSONObject();
        obj.put("user", user);
        obj.put("id", 1111111);
        obj.put("text", content);			
        String result = restTemplate.postForObject(url, obj.toString(),String.class);
        System.out.println(result);
    }

执行结果：

###2.解决办法 在使用RestTemplate发送post请求的时候，设置编码方式为UTF-8。代码如下：

@Test
public void test9() throws UnsupportedEncodingException{
        String url = "http://localhost:8080/test";
        JSONObject content = new JSONObject();
        content.put("content","内容内容内容内容内容内容内容");
        String user="用户";
        JSONObject obj = new JSONObject();
        obj.put("user", user);
        obj.put("id", 1111111);
        obj.put("text", content);
        //解决乱码					
        StringHttpMessageConverter m = new StringHttpMessageConverter(Charset.forName("UTF-8"));
        RestTemplate restTemplate = new RestTemplateBuilder().additionalMessageConverters(m).build();
        HttpHeaders headers = new HttpHeaders();
        MediaType type = MediaType.parseMediaType("application/json; charset=UTF-8");
        headers.setContentType(type);
        headers.add("Accept", MediaType.APPLICATION_JSON.toString()); 	             	         
        HttpEntity<String> formEntity = new HttpEntity<String>(obj.toString(), headers);    	 
        System.out.println(formEntity.getBody());
        String result = restTemplate.postForObject(url, formEntity, String.class);
        System.out.println(result);
}

执行结果：
从执行结果看，中文乱码已经不存在了。 ###3.出现乱码的原因 Spring中的RestTemplate其实也是封装了HttpClient，在项目中用RestTemplate的postForObject方法请求接口时出现乱码，既然出现乱码应该就是编码不一致导致的。下面分析一下原因：

1. 先看RestTemplate的postForObject方法

    @Override
    public <T> T postForObject(String url, Object request, Class<T> responseType, Object... uriVariables)
        throws RestClientException {
   
        RequestCallback requestCallback = httpEntityCallback(request, responseType);
        HttpMessageConverterExtractor<T> responseExtractor =new 
                        HttpMessageConverterExtractor<T>(responseType, getMessageConverters(), logger);
        return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
    }
   

HttpEntityCallback(request, responseType)：返回一个请求回调实现，它将给定的对象写入请求流。

/**
 * Returns a request callback implementation that writes the given object to the
 * request stream.
 */
protected <T> RequestCallback httpEntityCallback(Object requestBody, Type responseType) {
    return new HttpEntityRequestCallback(requestBody, responseType);
}

HttpEntityRequestCallback继承了AcceptHeaderRequestCallback； AcceptHeaderRequestCallback实现了RequestCallback；RequestCallback接口只有一个方法

public interface RequestCallback {

/**
 * Gets called by {@link RestTemplate#execute} with an opened {@code ClientHttpRequest}.
 * Does not need to care about closing the request or about handling errors:
 * this will all be handled by the {@code RestTemplate}.
 * @param request the active HTTP request
 * @throws IOException in case of I/O errors
 */
void doWithRequest(ClientHttpRequest request) throws IOException;

}

HttpEntityRequestCallback实现RequestCallback的doWithRequest方法的内容，主要是写入Request 对象流。 这两个类都使用HttpMessageConverter 的实现类来选择具体的Converter canRead canWrite
2. HttpMessageConverter是什么
从RestTemplate类的构造方法中可以看出，在初始化RestTemplate的时候就会加载一些HttpMessageConverter

/**
 * Create a new instance of the {@link RestTemplate} using default settings.
 * Default {@link HttpMessageConverter}s are initialized.
 */
public RestTemplate() {
    this.messageConverters.add(new ByteArrayHttpMessageConverter());
    this.messageConverters.add(new StringHttpMessageConverter());
    this.messageConverters.add(new ResourceHttpMessageConverter());
    this.messageConverters.add(new SourceHttpMessageConverter<Source>());
    this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());

    if (romePresent) {
        this.messageConverters.add(new AtomFeedHttpMessageConverter());
        this.messageConverters.add(new RssChannelHttpMessageConverter());
    }

    if (jackson2XmlPresent) {
        this.messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
    }
    else if (jaxb2Present) {
        this.messageConverters.add(new Jaxb2RootElementHttpMessageConverter());
    }

    if (jackson2Present) {
        this.messageConverters.add(new MappingJackson2HttpMessageConverter());
    }
    else if (gsonPresent) {
        this.messageConverters.add(new GsonHttpMessageConverter());
    }
}

从构造方法中可以看到加载了好几个类型的HttpMessageConverter。出现乱码的请求出现在中文中，中文又是一个String类型的，从上面HttpMessageConverter类名上，可以看出StringHttpMessageConverter是来处理中文的；出现乱码的情况肯定是编码出现了不一致，看一下StringHttpMessageConverter的编码是什么。
从下面的源码可以看出StringHttpMessageConverter的默认编码是ISO-8859-1

public class StringHttpMessageConverter extends AbstractHttpMessageConverter<String> {

    public static final Charset DEFAULT_CHARSET = Charset.forName("ISO-8859-1");
    private final List<Charset> availableCharsets;
    private boolean writeAcceptCharset = true;

    /**
     * A default constructor that uses {@code "ISO-8859-1"} as the default charset.
     * @see #StringHttpMessageConverter(Charset)
    */
    public StringHttpMessageConverter() {
        this(DEFAULT_CHARSET);
    }
    ……
}