我对 Java非常陌生，而且大部分时间都在自学，所以我开始构建一个小程序。我想做一个可以从本地磁盘中选择一个文件并将其作为 multipart/form-data POST 请求但带有进度条的上传。显然，用户必须授予 Java 小程序访问硬盘的权限。现在我已经完成了第一部分：用户可以使用一个JFileChooser对象选择一个文件，该对象可以方便地返回一个File对象。但我想知道接下来会发生什么。我知道这File.length()会给我文件的总大小（以字节为单位），但是如何将选定的内容发送File到网络，以及如何监控已发送的字节数？提前致谢。
SoaperGEM
问问题
59185 次
10 回答
39
要使用 HttpClient 检查进度，请将 MultipartRequestEntity 包裹在一个计算发送字节数的地方。包装器如下：
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import org.apache.commons.httpclient.methods.RequestEntity;
public class CountingMultipartRequestEntity implements RequestEntity {
private final RequestEntity delegate;
private final ProgressListener listener;
public CountingMultipartRequestEntity(final RequestEntity entity,
final ProgressListener listener) {
super();
this.delegate = entity;
this.listener = listener;
}
public long getContentLength() {
return this.delegate.getContentLength();
}
public String getContentType() {
return this.delegate.getContentType();
}
public boolean isRepeatable() {
return this.delegate.isRepeatable();
}
public void writeRequest(final OutputStream out) throws IOException {
this.delegate.writeRequest(new CountingOutputStream(out, this.listener));
}
public static interface ProgressListener {
void transferred(long num);
}
public static class CountingOutputStream extends FilterOutputStream {
private final ProgressListener listener;
private long transferred;
public CountingOutputStream(final OutputStream out,
final ProgressListener listener) {
super(out);
this.listener = listener;
this.transferred = 0;
}
public void write(byte[] b, int off, int len) throws IOException {
out.write(b, off, len);
this.transferred += len;
this.listener.transferred(this.transferred);
}
public void write(int b) throws IOException {
out.write(b);
this.transferred++;
this.listener.transferred(this.transferred);
}
}
}
然后实现一个更新进度条的 ProgressListener。
请记住，进度条更新不得在事件调度线程上运行。
于 2009-01-22T17:21:06.787 回答
12
更简单的countingEntity 将不依赖于特定的实体类型，而是扩展HttpEntityWrapped：
package gr.phaistos.android.util;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import org.apache.http.HttpEntity;
import org.apache.http.entity.HttpEntityWrapper;
public class CountingHttpEntity extends HttpEntityWrapper {
public static interface ProgressListener {
void transferred(long transferedBytes);
}
static class CountingOutputStream extends FilterOutputStream {
private final ProgressListener listener;
private long transferred;
CountingOutputStream(final OutputStream out, final ProgressListener listener) {
super(out);
this.listener = listener;
this.transferred = 0;
}
@Override
public void write(final byte[] b, final int off, final int len) throws IOException {
//// NO, double-counting, as super.write(byte[], int, int) delegates to write(int).
//super.write(b, off, len);
out.write(b, off, len);
this.transferred += len;
this.listener.transferred(this.transferred);
}
@Override
public void write(final int b) throws IOException {
out.write(b);
this.transferred++;
this.listener.transferred(this.transferred);
}
}
private final ProgressListener listener;
public CountingHttpEntity(final HttpEntity entity, final ProgressListener listener) {
super(entity);
this.listener = listener;
}
@Override
public void writeTo(final OutputStream out) throws IOException {
this.wrappedEntity.writeTo(out instanceof CountingOutputStream? out: new CountingOutputStream(out, this.listener));
}
}
于 2011-09-06T11:25:30.870 回答
5
侦听器返回的字节数与原始文件大小不同。所以，transferred++我没有修改它，而是修改了它transferred=len；这是写入输出流的实际字节数的长度。当我计算传输的总字节数之和时，它等于实际ContentLength返回的CountingMultiPartEntity.this.getContentLength();
public void write(byte[] b, int off, int len) throws IOException {
wrappedOutputStream_.write(b,off,len);
transferred=len;
listener_.transferred(transferred);
}
于 2012-04-26T09:17:42.150 回答
4
请记住，当网络中的中间组件（例如，ISP 的 HTTP 代理或服务器前的反向 HTTP 代理）比服务器更快地使用您的上传时，进度条可能会产生误导。
于 2008-11-01T00:37:17.187 回答
2
正如文森特发布的文章所述，您可以使用 Apache commons 来执行此操作。
小剪
DiskFileUpload upload = new DiskFileUpload();
upload.setHeaderEncoding(ConsoleConstants.UTF8_ENCODING);
upload.setSizeMax(1000000);
upload.setSizeThreshold(1000000);
Iterator it = upload.parseRequest((HttpServletRequest) request).iterator();
FileItem item;
while(it.hasNext()){
item = (FileItem) it.next();
if (item.getFieldName("UPLOAD FIELD"){
String fileName = item.getString(ConsoleConstants.UTF8_ENCODING);
byte[] fileBytes = item.get();
}
}
于 2008-10-31T21:57:54.807 回答
2
只是我的 2c 价值：
这是基于 tuler 的回答（在撰写本文时有一个错误）。我稍微修改了一下，所以这是我的 tuler 和 mmyers 答案版本（我似乎无法编辑他们的答案）。我想尝试使它更清洁和更快。CountingOutputStream除了错误（我在他们的答案的评论中讨论）之外，我对他们的版本的最大问题是每次写入都会创建一个新错误。这在内存方面可能会变得非常昂贵 - 大量的分配和垃圾收集。较小的问题是当它可以扩展时使用委托MultipartEntity。不知道他们为什么选择那个，所以我以我更熟悉的方式做了。如果有人知道这两种方法的优缺点，那就太好了。最后，FilterOutputStream#write(byte[], int,int) 方法只是在循环中调用 FilterOutputStream#write(byte)。FOS 文档建议子类覆盖此行为并使其更有效。最好的方法是让底层的 OutputStream 处理写入请求。
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import org.apache.http.entity.mime.HttpMultipartMode;
import org.apache.http.entity.mime.MultipartEntity;
public class CountingMultiPartEntity extends MultipartEntity {
private UploadProgressListener listener_;
private CountingOutputStream outputStream_;
private OutputStream lastOutputStream_;
// the parameter is the same as the ProgressListener class in tuler's answer
public CountingMultiPartEntity(UploadProgressListener listener) {
super(HttpMultipartMode.BROWSER_COMPATIBLE);
listener_ = listener;
}
@Override
public void writeTo(OutputStream out) throws IOException {
// If we have yet to create the CountingOutputStream, or the
// OutputStream being passed in is different from the OutputStream used
// to create the current CountingOutputStream
if ((lastOutputStream_ == null) || (lastOutputStream_ != out)) {
lastOutputStream_ = out;
outputStream_ = new CountingOutputStream(out);
}
super.writeTo(outputStream_);
}
private class CountingOutputStream extends FilterOutputStream {
private long transferred = 0;
private OutputStream wrappedOutputStream_;
public CountingOutputStream(final OutputStream out) {
super(out);
wrappedOutputStream_ = out;
}
public void write(byte[] b, int off, int len) throws IOException {
wrappedOutputStream_.write(b,off,len);
++transferred;
listener_.transferred(transferred);
}
public void write(int b) throws IOException {
super.write(b);
}
}
}
于 2010-07-01T03:33:37.660 回答
1
查看HTTP 客户端以将文件上传到网络。它应该能够做到这一点。我不确定如何获取进度条，但它会涉及以某种方式查询该 API。
于 2008-10-31T19:55:43.917 回答
1
Apache common 是非常好的选择。Apache common 允许您配置以下内容。
- 配置（xml文件）最大文件大小/上传文件大小
- 目标路径（保存上传文件的位置）
- 设置温度。文件夹来交换文件，这样文件上传会很快。
于 2009-04-16T12:25:04.590 回答
1
如果不想创建类，您可以从其他答案中覆盖您正在使用的AbstractHttpEntity类子类或实现方法。public void writeTo(OutputStream outstream)
使用FileEntity实例的示例：
FileEntity fileEntity = new FileEntity(new File("img.jpg")){
@Override
public void writeTo(OutputStream outstream) throws IOException {
super.writeTo(new BufferedOutputStream(outstream){
int writedBytes = 0;
@Override
public synchronized void write(byte[] b, int off, int len) throws IOException {
super.write(b, off, len);
writedBytes+=len;
System.out.println("wrote: "+writedBytes+"/"+getContentLength()); //Or anything you want [using other threads]
}
});
}
};
于 2016-04-03T12:13:43.070 回答