【resttemplate】RestTemplate返回值乱码问题分析与解决

原创

morris131 2023-10-16 09:16:38 博主文章分类：springboot ©著作权

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使用RestTemplate发送请求时，如果接口返回值中包含中文就会出现乱码：

RestTemplate restTemplate = new RestTemplate();
String result = restTemplate.getForObject("http://www.baidu.com", String.class);
System.out.println(result);

运行结果如下：

<!DOCTYPE html>
<!--STATUS OK--><html> <head><meta http-equiv=content-type content=text/html;charset=utf-8><meta http-equiv=X-UA-Compatible content=IE=Edge><meta content=always name=referrer><link rel=stylesheet type=text/css href=http://s1.bdstatic.com/r/www/cache/bdorz/baidu.min.css><title>ç™¾åº¦ä¸€ä¸‹ï¼Œä½ å°±çŸ¥é“</title></head> <body link=#0000cc> <div id=wrapper> <div id=head> <div class=head_wrapper> <div class=s_form> <div class=s_form_wrapper> <div id=lg> <img hidefocus=true src=//www.baidu.com/img/bd_logo1.png width=270 height=129> </div> <form id=form name=f action=//www.baidu.com/s class=fm> <input type=hidden name=bdorz_come value=1> <input type=hidden name=ie value=utf-8> <input type=hidden name=f value=8> <input type=hidden name=rsv_bp value=1> <input type=hidden name=rsv_idx value=1> <input type=hidden name=tn value=baidu><span class="bg s_ipt_wr"><input id=kw name=wd class=s_ipt value maxlength=255 autocomplete=off autofocus></span><span class="bg s_btn_wr"><input type=submit id=su value=ç™¾åº¦ä¸€ä¸‹ class="bg s_btn"></span> </form> </div> </div> <div id=u1> <a href=http://news.baidu.com name=tj_trnews class=mnav>æ–°é—»</a> <a href=http://www.hao123.com name=tj_trhao123 class=mnav>hao123</a> <a href=http://map.baidu.com name=tj_trmap class=mnav>åœ°å›¾</a> <a href=http://v.baidu.com name=tj_trvideo class=mnav>è§†é¢‘</a> <a href=http://tieba.baidu.com name=tj_trtieba class=mnav>è´´å§</a> <noscript> <a href=http://www.baidu.com/bdorz/login.gif?login&tpl=mn&u=http%3A%2F%2Fwww.baidu.com%2f%3fbdorz_come%3d1 name=tj_login class=lb>ç™»å½•</a> </noscript> <script>document.write('<a href="http://www.baidu.com/bdorz/login.gif?login&tpl=mn&u='+ encodeURIComponent(window.location.href+ (window.location.search === "" ? "?" : "&")+ "bdorz_come=1")+ '" name="tj_login" class="lb">ç™»å½•</a>');</script> <a href=//www.baidu.com/more/ name=tj_briicon class=bri style="display: block;">æ›´å¤šäº§å“</a> </div> </div> </div> <div id=ftCon> <div id=ftConw> <p id=lh> <a href=http://home.baidu.com>å
³äºŽç™¾åº¦</a> <a href=http://ir.baidu.com>About Baidu</a> </p> <p id=cp>©2017 Baidu <a href=http://www.baidu.com/duty/>ä½¿ç”¨ç™¾åº¦å‰å¿
è¯»</a>  <a href=http://jianyi.baidu.com/ class=cp-feedback>æ„è§åé¦ˆ</a> äº¬ICPè¯030173å·  <img src=//www.baidu.com/img/gs.gif> </p> </div> </div> </div> </body> </html>

从源码分析原因

这个问题我首先想到的是RestTemplate的MessageConverter消息转换器，首先找到RestTemplate解析response的地方。

org.springframework.web.client.HttpMessageConverterExtractor#extractData

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()) {
                        ResolvableType resolvableType = ResolvableType.forType(this.responseType);
                        logger.debug("Reading to [" + resolvableType + "]");
                    }
                    return (T) genericMessageConverter.read(this.responseType, null, responseWrapper);
                }
            }
            if (this.responseClass != null) {
                if (messageConverter.canRead(this.responseClass, contentType)) {
                    if (logger.isDebugEnabled()) {
                        String className = this.responseClass.getName();
                        logger.debug("Reading to [" + className + "] as \"" + contentType + "\"");
                    }
                    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 UnknownContentTypeException(this.responseType, contentType,
            response.getRawStatusCode(), response.getStatusText(), response.getHeaders(),
            getResponseBody(response));
}

HttpMessageConverter消息转换器

RestTemplate的构造方法中默认内置了下面7个消息转换器：

ByteArrayHttpMessageConverter
StringHttpMessageConverter
ResourceHttpMessageConverter
SourceHttpMessageConverter
AllEncompassingFormHttpMessageConverter
Jaxb2RootElementHttpMessageConverter
MappingJackson2HttpMessageConverter

StringHttpMessageConverter

上面的代码最终会调用StringHttpMessageConverter来对结果进行转换。

canRead()主要根据返回结果的类型和mediaType来进行校验是否可以是否此消息转换器进行转换。

org.springframework.http.converter.AbstractHttpMessageConverter#canRead(java.lang.Class<?>, org.springframework.http.MediaType)

public boolean canRead(Class<?> clazz, @Nullable MediaType mediaType) {
    return supports(clazz) && canRead(mediaType);
}

public boolean supports(Class<?> clazz) {
    return String.class == clazz;
}

protected boolean canRead(@Nullable MediaType mediaType) {
    if (mediaType == null) {
        return true;
    }
    for (MediaType supportedMediaType : getSupportedMediaTypes()) {
        if (supportedMediaType.includes(mediaType)) {
            return true;
        }
    }
    return false;
}

StringHttpMessageConverter支持restTemplate.getForObject传入的class为String类型，mediaType支持所有，在构造方法中指定了MediaType.ALL

public StringHttpMessageConverter() {
    this(DEFAULT_CHARSET);
}

/**
 * A constructor accepting a default charset to use if the requested content
 * type does not specify one.
 */
public StringHttpMessageConverter(Charset defaultCharset) {
    super(defaultCharset, MediaType.TEXT_PLAIN, MediaType.ALL);
}

当前面的校验通过后，会调用readInternal()对结果进行转换：
org.springframework.http.converter.StringHttpMessageConverter#readInternal

protected String readInternal(Class<? extends String> clazz, HttpInputMessage inputMessage) throws IOException {
    Charset charset = getContentTypeCharset(inputMessage.getHeaders().getContentType());
    return StreamUtils.copyToString(inputMessage.getBody(), charset);
}

getContentTypeCharset()会判断使用何种编码方法对结果进行编码，这里使用了默认的编码：
org.springframework.http.converter.StringHttpMessageConverter#getContentTypeCharset

private Charset getContentTypeCharset(@Nullable MediaType contentType) {
    if (contentType != null && contentType.getCharset() != null) {
        return contentType.getCharset();
    }
    else if (contentType != null &&
            (contentType.isCompatibleWith(MediaType.APPLICATION_JSON) ||
                    contentType.isCompatibleWith(APPLICATION_PLUS_JSON))) {
        // Matching to AbstractJackson2HttpMessageConverter#DEFAULT_CHARSET
        return StandardCharsets.UTF_8;
    }
    else {
        Charset charset = getDefaultCharset();
        Assert.state(charset != null, "No default charset");
        return charset;
    }
}

在StringHttpMessageConverter的构造方法中指定了默认的编码是ISO_8859_1，这就是乱码的根本原因。

public static final Charset DEFAULT_CHARSET = StandardCharsets.ISO_8859_1;

public StringHttpMessageConverter() {
    this(DEFAULT_CHARSET);
}

我们只要将ISO_8859_1修改为UTF-8就能解决乱码问题。

修改StringHttpMessageConverter的编码

方式一：简单粗暴，从源码可得知第一个位置的类型是StringHttpMessageConverter，直接取出来将编码修改为UTF-8。

RestTemplate restTemplate = new RestTemplate();
StringHttpMessageConverter stringHttpMessageConverter = (StringHttpMessageConverter) restTemplate.getMessageConverters().get(1);
stringHttpMessageConverter.setDefaultCharset(StandardCharsets.UTF_8);
String result = restTemplate.getForObject("http://www.baidu.com", String.class);
System.out.println(result);

方式二：推荐使用，通过类型来找到StringHttpMessageConverter，将编码修改为UTF-8。

RestTemplate restTemplate = new RestTemplate();
List<HttpMessageConverter<?>> messageConverters = restTemplate.getMessageConverters();
for (HttpMessageConverter<?> messageConverter : messageConverters) {
    if(messageConverter instanceof StringHttpMessageConverter) {
        ((StringHttpMessageConverter) messageConverter).setDefaultCharset(StandardCharsets.UTF_8);
    }
}
String result = restTemplate.getForObject("http://www.baidu.com", String.class);
System.out.println(result);

方式三：将所有的消息转换器的编码都修改为UTF-8

RestTemplate restTemplate = new RestTemplate();
List<HttpMessageConverter<?>> messageConverters = restTemplate.getMessageConverters();
for (HttpMessageConverter<?> messageConverter : messageConverters) {
    if(messageConverter instanceof AbstractHttpMessageConverter) {
        ((AbstractHttpMessageConverter) messageConverter).setDefaultCharset(StandardCharsets.UTF_8);
    } else if(messageConverter instanceof FormHttpMessageConverter) {
        ((FormHttpMessageConverter) messageConverter).setCharset(StandardCharsets.UTF_8);
        ((FormHttpMessageConverter) messageConverter).setMultipartCharset(StandardCharsets.UTF_8);
    }
}
String result = restTemplate.getForObject("http://www.baidu.com", String.class);
System.out.println(result);

MappingJackson2HttpMessageConverter

最后来学习一下MappingJackson2HttpMessageConverter，只有MappingJackson2HttpMessageConverter是GenericHttpMessageConverter类型，只有Response的header中的Content-type是application/json才会解析：

public MappingJackson2HttpMessageConverter() {
    this(Jackson2ObjectMapperBuilder.json().build());
}

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

MappingJackson2HttpMessageConverter使用了ObjectMapper来进行序列化和反序列化。