ExtJS 4 Spring 3 文件上传。服务器发送错误的响应内容类型

Question

我正在使用 ExtJS 4 前端和 Spring 3 作为后端创建文件上传。文件上传有效，但服务器的响应内容类型错误。当我使用 Jackson 序列化的Map<String, Object> 发送{success:true} 时，ExtJS 返回错误

Uncaught Ext.Error: You're trying to decode an invalid JSON String: <pre style="word-wrap: break-word; white-space: pre-wrap;">{"success":true}</pre>

为什么我的回复被<pre> 标签包裹？我已经搜索了 found out，例如我应该将响应类型更改为 text/html。但是changing content type in servlet response 没有帮助

@RequestMapping(value = "/upload", method = RequestMethod.POST)
public @ResponseBody Map<String, Object> upload(
    FileUpload uploadItem, BindingResult result, HttpServletResponse response) {

    response.setContentType("text/html");

    // File processing   

    Map<String, Object> jsonResult = new HashMap<String, Object>();
    jsonResult.put("success", Boolean.TRUE);
    return jsonResult;
}

当我将upload 方法的返回值更改为String 时，一切正常，但我想返回Map 并让Jackson 对其进行序列化

@RequestMapping(value = "/upload", method = RequestMethod.POST)
public @ResponseBody String upload(
    FileUpload uploadItem, BindingResult result, HttpServletResponse response) {

    // File processing   

    return "{success:true}";
}

我的 Spring 配置

<bean 
    id="stringHttpMessageConverter" 
    class="org.springframework.http.converter.StringHttpMessageConverter">
</bean>
<bean 
    id="jacksonMessageConverter" 
    class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter"/>  
<bean    
    class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
    <property name="messageConverters">
        <list>
            <ref bean="jacksonMessageConverter"/>
            <ref bean="stringHttpMessageConverter" />
        </list>
    </property>
</bean>

如何告诉Spring返回正确的内容类型？当其他方法的响应被正确解释时，为什么这个方法的响应不正确？

Answer 1

您需要将响应的内容类型设置为“text/html”。 如果content-type是“application/json”就会有这个问题。很奇怪。

Answer 2

如果你只需要返回成功的值，你可以返回布尔值：

@RequestMapping(value = "/upload", method = RequestMethod.POST)
public @ResponseBody boolean upload(
    FileUpload uploadItem, BindingResult result, HttpServletResponse response) {

    return true; //or false
}

Answer 3

嗯，不是最好的解决方案，但它解决了问题。我创建了类，其中包含Map 以及将参数添加到Map 的方法。还有实现方法toString()。

public class ExtJSJsonResponse {

    /** Parameters to serialize to JSON */
    private Map<String, Object> params = new HashMap<String, Object>();

    /**
     * Add arbitrary parameter for JSON serialization. 
     * Parameter will be serialized as {"key":"value"};
     * @param key name of parameter
     * @param value content of parameter
     */
    @JsonIgnore
    public void addParam(String key, Object value) {
        params.put(key, value);
    }

    /**
     * Gets all parameters. Also is annotated with <code>@JsonValue</code>.
     * @return all params with keys as map
     */
    @JsonValue
    public Map<String, Object> getParams() {
        return params;
    }

    /**
     * Returns specified parameter by <code>key</code> as string "key":"value"
     * @param key parameter key 
     * @return  "key":"value" string or empty string when there is no parameter 
     *          with specified key
     */
    private String paramToString(String key) {
        return params.containsKey(key) 
            ? "\"" + key + "\":\"" + params.get(key) + "\""
            : "";
    }

    /**
     * Manually transforms map parameters to JSON string. Used when ExtJS fails 
     * to decode Jackson response. i.e. when uploading file.
     * @return 
     */
    @Override
    @JsonIgnore
    public String toString() {
        StringBuilder sb = new StringBuilder("{");
        String delimiter = "";

        for (String key : params.keySet()) {
            sb.append(delimiter);
            sb.append(paramToString(key));
            delimiter = ",";
        }

        sb.append("}");
        return sb.toString();
    }
}

所以当Uncaught Ext.Error: You're trying to decode an invalid JSON String 出现时，您只需这样做

@RequestMapping(value = "/upload", method = RequestMethod.POST)
public @ResponseBody String upload(
    FileUpload uploadItem, BindingResult result, HttpServletResponse response) {
    ExtJSJsonResponse response = new ExtJSJsonResponse();

    // File processing
    response.addParam("success", true);
    response.addParam("message", "All OK");   

    return response.toString();
}

在其他没有序列化问题的方法中，您可以简单地调用return response;，它将自动序列化。

方法toString() 仅适用于简单的类，例如String。对于更复杂的类，您必须更改它。

Answer 4

我认为你可以使用 Spring 的 @RequestMapping 注解的“produces”属性：

@RequestMapping(value = "/upload", method = RequestMethod.POST, produces = MediaType.TEXT_HTML_VALUE)
public @ResponseBody Map<String, Object> upload(
    FileUpload uploadItem, BindingResult result, HttpServletResponse response) {

    // File processing   

    Map<String, Object> jsonResult = new HashMap<String, Object>();
    jsonResult.put("success", Boolean.TRUE);
    return jsonResult;
}

在配置文件中，你应该使这个 Content-Type 可用：

<bean id="jacksonMessageConverter" class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
    <property name="supportedMediaTypes">
        <array>
            <value>text/html</value>
            <value>application/json</value>
        </array>
    </property>
</bean>  

这在 Spring 3.1.1.RELEASE 中可用，可能在旧版本中不起作用。