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<h1 id="_1">文件下载开发指导</h1>
<h2 id="_2">服务提供者开发</h2>
<p>文件下载支持采用 Spring MVC 和 Jax RS 开发。 因为文件下载都是 GET 方法， 因此两者的使用差异很小， 这里的例子只提供
Spring MVC 。 </p>
<ul>
<li>File</li>
</ul>
<p>最简单的例子，接口的返回参数声明为 File 类型的参数， 即可定义一个下载接口。 </p>
<pre><code>@GetMapping(path = &quot;/file&quot;)
public File file(String name)
</code></pre>
<ul>
<li>Part</li>
</ul>
<p>如果需要根据请求参数动态创建临时文件，下载完成后，将临时文件删除，可以采用 Part 类型的参数。</p>
<pre><code>@GetMapping(path = &quot;/file&quot;)
public Part file(String content) throws IOException {
File file = createTempFile(content);
return new FilePart(null, file)
.setDeleteAfterFinished(true)
.setSubmittedFileName(&quot;test.txt&quot;);
}
</code></pre>
<ul>
<li>Resource</li>
</ul>
<p>可以将接口声明为 org.springframework.core.io.Resource。 由于resource不一定表示文件下载，所以需要通过
@ApiResponse 标识这是一个文件下载场景</p>
<p>以ByteArrayResource为例说明：</p>
<pre><code>@GetMapping(path = &quot;/resource&quot;)
@ApiResponses({
@ApiResponse(code = 200, response = File.class, message = &quot;&quot;)
})
public Resource resource() {
return new ByteArrayResource(bytes) {
@Override
public String getFilename() {
return &quot;resource.txt&quot;;
}
};
}
</code></pre>
<p>上例中，因为ByteArrayResource没有文件名的概念，所以需要实现Resource的getFilename方法，也可以通过ResponseEntity
进行包装：</p>
<pre><code>@GetMapping(path = &quot;/resource&quot;)
@ApiResponses({
@ApiResponse(code = 200, response = File.class, message = &quot;&quot;)
})
public ResponseEntity&lt;Resource&gt; resource() {
return ResponseEntity
.ok()
.header(HttpHeaders.CONTENT_TYPE, MediaType.TEXT_PLAIN_VALUE)
.header(HttpHeaders.CONTENT_DISPOSITION, &quot;attachment;filename=resource.txt&quot;)
.body(resource);
}
</code></pre>
<ul>
<li>InputStream</li>
</ul>
<p>一样的， 使用 InputStream 需要 @ApiResponse 标识这是一个文件下载场景</p>
<pre><code>@GetMapping(path = &quot;/inputStream&quot;)
@ApiResponses({
@ApiResponse(code = 200, response = File.class, message = &quot;&quot;),
})
public ResponseEntity&lt;InputStream&gt; download() throws IOException {
return ResponseEntity
.ok()
.header(HttpHeaders.CONTENT_TYPE, MediaType.TEXT_PLAIN_VALUE)
.header(HttpHeaders.CONTENT_DISPOSITION, &quot;attachment;filename=resource.txt&quot;)
.body(stream);
}
</code></pre>
<p>在下载完成后，ServiceComb会自动关闭stream，开发人员不必再关注。</p>
<ul>
<li>文件类型判定</li>
</ul>
<p>只要没有通过ResponseEntity直接设置HttpHeaders.CONTENT_TYPE，ServiceComb都会尝试通过File、Part、Resource中的文件名后缀进行自动判定。</p>
<p>ServiceComb使用java的mime type机制进行文件类型判定，如果业务场景中的文件后缀无法被识别，ServiceComb会默认处理为application/octet-stream</p>
<p>如果这不满足要求，假设文件后缀为xyz，期望文件类型为application/file-xyz，以下方式任选一种均可解决：</p>
<ol>
<li>通过Java的mime type机制扩展</li>
</ol>
<p>在META-INF目录下，创建mime.types文件，其内容为：</p>
<pre><code>application/file-xyz xyz
</code></pre>
<pre><code>2. 在业务代码中通过Part指定
</code></pre>
<pre><code>@GetMapping(path = &quot;/tempFilePart&quot;)
public Part tempFilePart(String content) throws IOException {
File file = createTempFile(content);
return new FilePart(null, file)
.setDeleteAfterFinished(true)
.contentType(&quot;application/file-xyz&quot;)
.setSubmittedFileName(&quot;tempFilePart.txt&quot;);
}
</code></pre>
<pre><code>3. 在业务代码中通过ResponseEntity指定
</code></pre>
<pre><code>@GetMapping(path = &quot;/tempFileEntity&quot;)
public ResponseEntity&lt;Part&gt; tempFileEntity(String content) throws IOException {
File file = createTempFile(content);
return ResponseEntity
.ok()
.header(HttpHeaders.CONTENT_TYPE, &quot;application/file-xyz&quot;)
.header(HttpHeaders.CONTENT_DISPOSITION, &quot;attachment;filename=tempFileEntity.txt&quot;)
.body(new FilePart(null, file)
.setDeleteAfterFinished(true));
}
</code></pre>
<ul>
<li>指定文件名</li>
</ul>
<p>只要没有通过ResponseEntity直接设置HttpHeaders.CONTENT_DISPOSITION，ServiceComb都会尝试通过File、Part、Resource中的文件名生成HttpHeaders.CONTENT_DISPOSITION，假设文件名为file.txt，则生成的数据如下：</p>
<pre><code>Content-Disposition: attachment;filename=file.txt;filename*=utf-8’’file.txt
</code></pre>
<p>不仅仅生成filename，还生成了filename*，这是因为如果文件名中出现了中文、空格，并且filename正确地做了encode，ie、chrome都没有问题，但是firefox直接将encode后的串当作文件名直接使用了。firefox按照<a href="https://tools.ietf.org/html/rtf6266">https://tools.ietf.org/html/rtf6266</a>，只对filename*进行解码。</p>
<p>如果业务代码中直接设置Content-Disposition，需要自行处理多浏览器支持的问题。</p>
<p>文件下载的更多用法可以通过下载 java-chassis 源码， 查看 DownloadSchema 里面的例子。</p>
<h2 id="_3">服务消费者开发</h2>
<p>消费者统一使用 org.apache.servicecomb.foundation.vertx.http.ReadStreamPart 处理文件下载。
可以使用透明 RPC 方式， </p>
<pre><code>public interface ……{
ReadStreamPart download1(……);
ReadStreamPart download2(……);
}
</code></pre>
<p>或者 RestTemplate</p>
<pre><code>ReadStreamPart part = restTemplate.getForObject(url, ReadStreamPart.class);
</code></pre>
<p>ReadStreamPart提供了一系列方法，将数据流保存为本地数据：</p>
<pre><code>org.apache.servicecomb.foundation.vertx.http.ReadStreamPart.saveAsBytes()
org.apache.servicecomb.foundation.vertx.http.ReadStreamPart.saveAsString()
org.apache.servicecomb.foundation.vertx.http.ReadStreamPart.saveToFile(String)
org.apache.servicecomb.foundation.vertx.http.ReadStreamPart.saveToFile(File, OpenOptions)
</code></pre>
<p><strong><em>注意：</em></strong></p>
<ul>
<li>在得到ReadStreamPart实例时，并没有完成文件内容的下载，调用save系列方法才开始真正从网络上读取文件数据。</li>
<li>如果使用saveAsBytes、saveAsString，数据是直接保存在内存中的，如果下载的文件很大，会导致内存溢出。</li>
<li>save系列方法，返回的都是CompletableFuture对象， 如果要阻塞等待下载完成，通过future.get()即可；
如果通过future.whenComplete进行异步回调处理，要注意回调是发生在网络线程中的，此时需要遵守reactive的线程规则。</li>
</ul>
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