1. 程式人生 > >RestTemplate 微信接口 text/plain HttpMessageConverter

RestTemplate 微信接口 text/plain HttpMessageConverter

異常 found 處理 占位符 構造函數 conn pes exe include

一、背景介紹

使用 Spring Boot 寫項目,需要用到微信接口獲取用戶信息。

在 Jessey 和 Spring RestTemplate 兩個 Rest 客戶端中,想到盡量不引入更多的東西,然後就選擇了 Spring RestTemplate 作為 網絡請求的 Client,然後就被微信接口擺了一道,然後踩了一個 RestTemplate 的坑。

二、第一個坑:被微信擺了一道

報錯信息是:

org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [class com.solar.app.model.weixin.WxBaseUserInfo] and content type [text/plain]
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之所以被微信擺了一道,是因為微信接口文檔雖說返回的是 Json 數據,但是同時返回的 Header 裏面的 Content-Type 值確是 text/plain 的!!

最終結果就是導致 RestTemplate 把數據從 HttpResponse 轉換成 Object 的時候,找不到合適的 HttpMessageConverter 來轉換!

我使用 RestTemplate 時配置 Bean 時使用默認的構造函數:

@Bean
RestTemplate restTemplate(){
    return new RestTemplate();
}
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繼續看 RestTemplate() 默認構造函數都幹了啥:

/**
 * 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());// tag1
    }
    else if (gsonPresent) {
        this.messageConverters.add(new GsonHttpMessageConverter());
    }
}
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可以看到,RestTemplate() 默認構造函數設置了一系列 HttpMessageConverter。

我的項目裏引入了 com.fasterxml.jackson,所以 RestTemplate() 會構造一個 MappingJackson2HttpMessageConverter 加到它的 messageConverters 中,即上面的代碼:【tag1】

繼續看 MappingJackson2HttpMessageConverter() 默認構造函數:

/**
 * Construct a new {@link MappingJackson2HttpMessageConverter} using default configuration
 * provided by {@link Jackson2ObjectMapperBuilder}.
 */
public MappingJackson2HttpMessageConverter() {
    this(Jackson2ObjectMapperBuilder.json().build());
}

/**
 * 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"));
}
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可以看到,默認構造的 MappingJackson2HttpMessageConverter 中的 supportedMediaTypes 只支持:application/json 的 MediaType。

再看 RestTemplate 請求的流程,會執行到這裏:

/**
 * Execute the given method on the provided URI.
 * <p>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}
 */
protected <T> T doExecute(URI url, HttpMethod method, RequestCallback requestCallback,
        ResponseExtractor<T> 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);// tag2
        }
        else {
            return null;
        }
    }
    catch (IOException ex) {
        String resource = url.toString();
        String query = url.getRawQuery();
        resource = (query != null ? resource.substring(0, resource.indexOf(query) - 1) : resource);
        throw new ResourceAccessException("I/O error on " + method.name() +
                " request for \"" + resource + "\": " + ex.getMessage(), ex);
    }
    finally {
        if (response != null) {
            response.close();
        }
    }
}
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從 HttpResponse 中獲取數據實際是執行 【tag2】。這個操作由 HttpMessageConverterExtractor 類來完成:

@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);// tag3, 微信返回的是 text/plain

    for (HttpMessageConverter<?> messageConverter : this.messageConverters) {
        if (messageConverter instanceof GenericHttpMessageConverter) {
            GenericHttpMessageConverter<?> genericMessageConverter = (GenericHttpMessageConverter<?>) messageConverter;
            if (genericMessageConverter.canRead(this.responseType, null, contentType)) {// tag4
                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);
            }
        }
    }

    throw new RestClientException("Could not extract response: no suitable HttpMessageConverter found " +
            "for response type [" + this.responseType + "] and content type [" + contentType + "]");
}
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【tag4】處的代碼用於判斷 MappingJackson2HttpMessageConverter 是否支持 【tag3】 類型的 MediaType。

AbstractJackson2HttpMessageConverter:

@Override
public boolean canRead(Type type, Class<?> contextClass, MediaType mediaType) {
    if (!canRead(mediaType)) {// tag5
        return false;
    }
    JavaType javaType = getJavaType(type, contextClass);
    if (!logger.isWarnEnabled()) {
        return this.objectMapper.canDeserialize(javaType);
    }
    AtomicReference<Throwable> causeRef = new AtomicReference<Throwable>();
    if (this.objectMapper.canDeserialize(javaType, causeRef)) {
        return true;
    }
    logWarningIfNecessary(javaType, causeRef.get());
    return false;
}
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AbstractHttpMessageConverter:

/**
 * Returns {@code true} if any of the {@linkplain #setSupportedMediaTypes(List)
 * supported} media types {@link MediaType#includes(MediaType) include} the
 * given media type.
 * @param mediaType the media type to read, can be {@code null} if not specified.
 * Typically the value of a {@code Content-Type} header.
 * @return {@code true} if the supported media types include the media type,
 * or if the media type is {@code null}
 */
protected boolean canRead(MediaType mediaType) {
    if (mediaType == null) {
        return true;
    }
    for (MediaType supportedMediaType : getSupportedMediaTypes()) {
        if (supportedMediaType.includes(mediaType)) {
            return true;
        }
    }
    return false;
}
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一路追蹤下來,可以確定,只要讓 MappingJackson2HttpMessageConverter 能處理頭部 Content-Type 為 text/plain 類型的 Json 返回值的話,我們就能讓其幫我們把 Json 反序列化成我們要的對象。

我們繼承 MappingJackson2HttpMessageConverter 並在構造過程中設置其支持的 MediaType 類型即可:

public class WxMappingJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter {
    public WxMappingJackson2HttpMessageConverter(){
        List<MediaType> mediaTypes = new ArrayList<>();
        mediaTypes.add(MediaType.TEXT_PLAIN);
        setSupportedMediaTypes(mediaTypes);// tag6
    }
}
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【tag6】的代碼,會覆蓋其默認的 MediaType 設置。

然後把這個 WxMappingJackson2HttpMessageConverter 追加到 RestTemplate 的 messageConverters 消息轉換鏈中去:

@Bean
RestTemplate restTemplate(){
    RestTemplate restTemplate = new RestTemplate();
    restTemplate.getMessageConverters().add(new WxMappingJackson2HttpMessageConverter());
    return restTemplate;
}
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我既不推薦把 WxMappingJackson2HttpMessageConverter 實例當作構造 RestTemplate 時的參數來構造 RestTemplate,也不推薦 使用新的 WxMappingJackson2HttpMessageConverter 替換 RestTemplate 默認構造中創建的 MappingJackson2HttpMessageConverter 實例,因為這兩種方式都會導致 Content-Type 為 application/json 的 Json 響應沒有轉換器來反序列化,所以最佳的方式還是“追加”。

三、第二個坑:RestTemplate 的使用

其實也不算坑,主要是我太蠢。
一開始我是這樣寫的:

@Override
public WxBaseUserInfo getBaseUserInfo(String access_token, String openid) {
    String url = "https://api.weixin.qq.com/sns/userinfo";

    Map<String, String> params = new HashMap<>();
    params.put("access_token", access_token);
    params.put("openid", openid);
    params.put("lang", "zh_CN");

    WxBaseUserInfo result = null;
    try{
        result = restTemplate.getForObject(url, WxBaseUserInfo.class, params);
    }catch (RestClientException e){
        LOGGER.error("getBaseUserInfo", e);
    }
    return result;
}
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但是,微信竟然提示我缺失 access_token !後來看 官方示例:REST in Spring 3: RestTemplate 才發現我用錯了!正確用法是這樣:

@Override
public WxBaseUserInfo getBaseUserInfo(String access_token, String openid) {
    String url = "https://api.weixin.qq.com/sns/userinfo?" +
            "access_token={access_token}&openid={openid}&lang={lang}";// tag7

    Map<String, String> params = new HashMap<>();
    params.put("access_token", access_token);
    params.put("openid", openid);
    params.put("lang", "zh_CN");

    WxBaseUserInfo result = null;
    try{
        result = restTemplate.getForObject(url, WxBaseUserInfo.class, params);
    }catch (RestClientException e){
        LOGGER.error("getBaseUserInfo", e);
    }
    return result;
}
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註意以上【tag7】處占位符的用法!

然後,還是有問題:如果因為 access_token 或 openid 的不合法,微信接口會返回一下格式的數據:

{ 
    "errcode":40003,"errmsg":"invalid openid"
}
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經測試,當微信接口返回以上格式的錯誤信息 json 後,restTemplate.getForObject() 返回的仍然是一個我們想要的 WxBaseUserInfo 對象,但是該對象的任何字段都為 null!

經查,微信接口所有的錯誤時的 json 信息格式都如以上格式。然後迫不得己用一種很挫的方式來做“接口異常”處理:

public class WxError {

    private Integer errcode;

    private String errmsg;

    // getter and setter...

    @Override
    public String toString() {
        return "WxError{" +
                "errcode=" + errcode +
                ", errmsg=‘" + errmsg + ‘\‘‘ +
                ‘}‘;
    }

    //---------- functions

    public boolean valid(){
        return errcode == null || errcode == 0;
    }
}
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定義一個公共的錯誤信息類作為父類,所有微信正常返回的數據對象繼承該錯誤類。

public class WxBaseUserInfo extends WxError {

    private String openid;

    private String nickname;

    private Integer sex;

    private String province;

    private String city;

    private String country;

    private String headimgurl;

    private List<String> privilege;// tag8

    private String unionid;

    // getter and setter...

    @Override
    public String toString() {
        return "WxBaseUserInfo{" +
                "openid=‘" + openid + ‘\‘‘ +
                ", nickname=‘" + nickname + ‘\‘‘ +
                ", sex=" + sex +
                ", province=‘" + province + ‘\‘‘ +
                ", city=‘" + city + ‘\‘‘ +
                ", country=‘" + country + ‘\‘‘ +
                ", headimgurl=‘" + headimgurl + ‘\‘‘ +
                ", privilege=‘" + privilege + ‘\‘‘ +
                ", unionid=‘" + unionid + ‘\‘‘ +
                ‘}‘ + "  " + super.toString();
    }
}
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註意以上的【tag8】處,privilege 類型是 List! 如果類寫成 String 就會導致 Json 轉換失敗!

最終獲取用戶信息的方法變成了這樣子:

@Override
public WxBaseUserInfo getBaseUserInfo(String access_token, String openid) {
    String url = "https://api.weixin.qq.com/sns/userinfo?" +
            "access_token={access_token}&openid={openid}&lang={lang}";

    Map<String, String> params = new HashMap<>();
    params.put("access_token", access_token);
    params.put("openid", openid);
    params.put("lang", "zh_CN");

    WxBaseUserInfo result = null;
    try{
        result = restTemplate.getForObject(url, WxBaseUserInfo.class, params);
        if(null == result || !result.valid()){// tag9
            LOGGER.error("getBaseUserInfo invalid: " + result);
            result = null;
        }
    }catch (RestClientException e){
        LOGGER.error("getBaseUserInfo", e);
    }
    return result;
}
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我這裏的處理的當微信接口未能返回預期的數據時,此方法返回 null。換成 Java8 的 Optional 來處理應該會更好。大家按需處理吧。

四、總結

就這麽一個簡單的過程,我竟然踩了這麽多坑,真是蠢。不過對也些東西的認識也加深了。如果您有更優雅的方式,請留言或者貼個鏈接呀,謝謝 :)

五、參考

  • REST in Spring 3: RestTemplate

http://blog.csdn.net/kinginblue/article/details/52706155

RestTemplate 微信接口 text/plain HttpMessageConverter