使用google-http-java-client提交多部分表单

Question

从 google-http-java-client* 文档中并不清楚如何发布带有文件字段的表单。

例如，我正在尝试使用 Google Cloud Print API 打印文档：

HttpRequestFactory httpRequestFactory = getHttpRequestFactory();

Map<String, Object> parameters = Maps.newHashMap();
parameters.put("printerId", printRequest.getPrinterId());
parameters.put("title", printRequest.getTitle());
parameters.put("contentType", printRequest.getContentType());
parameters.put("ticket", new Gson().toJson(printRequest.getOptions()));

MultipartContent content = new MultipartContent();
content.addPart(new MultipartContent.Part(new UrlEncodedContent(parameters)));
content.addPart(new MultipartContent.Part(
        new FileContent(printRequest.getContentType(), printRequest.getFile())));

try {
    HttpResponse response = httpRequestFactory.buildPostRequest(
            SubmitUrl, content).execute();
    System.out.println(IOUtils.toString(response.getContent()));
} catch (IOException e) {
    String message = String.format();
    System.out.println("Error submitting print job: " + e.getMessage());
}

很遗憾，这不起作用。API返回错误“请求需要打印机ID”，这对我来说似乎意味着请求格式不正确。我做错了什么？*我特别使用google-http-java-client，因为它可以自动刷新OAuth令牌等。请不要给出涉及使用其他HTTP客户端的解决方案。

- kuhnza

Answer 1

看起来我误解了如何将表单字段添加到多部分消息中。现在的工作代码如下：

HttpRequestFactory httpRequestFactory = getHttpRequestFactory(username);

Map<String, String> parameters = Maps.newHashMap();
parameters.put("printerid", printRequest.getPrinterId());
parameters.put("title", printRequest.getTitle());
parameters.put("contentType", printRequest.getContentType());

// Map print options into CJT structure
Map<String, Object> options = Maps.newHashMap();
options.put("version", "1.0");
options.put("print", printRequest.getOptions());
parameters.put("ticket", new Gson().toJson(options));

// Add parameters
MultipartContent content = new MultipartContent().setMediaType(
        new HttpMediaType("multipart/form-data")
                .setParameter("boundary", "__END_OF_PART__"));
for (String name : parameters.keySet()) {
    MultipartContent.Part part = new MultipartContent.Part(
            new ByteArrayContent(null, parameters.get(name).getBytes()));
    part.setHeaders(new HttpHeaders().set(
            "Content-Disposition", String.format("form-data; name=\"%s\"", name)));
    content.addPart(part);
}

// Add file
FileContent fileContent = new FileContent(
        printRequest.getContentType(), printRequest.getFile());
MultipartContent.Part part = new MultipartContent.Part(fileContent);
part.setHeaders(new HttpHeaders().set(
        "Content-Disposition", 
        String.format("form-data; name=\"content\"; filename=\"%s\"", printRequest.getFile().getName())));
content.addPart(part);

try {
    HttpResponse response = httpRequestFactory.buildPostRequest(
            SubmitUrl, content).execute();
    System.out.println(IOUtils.toString(response.getContent()));
} catch (IOException e) {
    ...
}

上述内容的最重要部分是覆盖默认的HttpMediaType以指定“multipart/form-data”，并将每个字段作为自己的部分添加，使用“Content-Disposition”标头指定表单字段名称。

- kuhnza

---

在代码片段 "printRequest.getContentType()" 中是什么？ - Jeryl Cook

哇，你会认为构建一个多部分请求会比那容易一些！但是谢谢，它对我有用。 - Barry Pitman