使用Java上传文件(带进度条)

Question

我对Java 非常陌生,并且大部分时间都在教我自己,所以我开始构建一个applet.我想创建一个可以从本地磁盘中选择文件并将其作为multipart/form-data POST请求上传但有进度条的文件.显然,用户必须授予Java applet访问硬盘驱动器的权限.现在我已经完成了第一部分工作:用户可以使用JFileChooser对象选择一个文件,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()将给我文件的总大小(以字节为单位),但是如何将所选内容发送File到网络,以及如何监控已发送的字节数？提前致谢.

Answer 1

要使用HttpClient检查进度,请将MultipartRequestEntity包装在计算发送字节数的周围.包装如下:

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Event Dispatch Thread上运行.

Answer 2

更简单的countEntity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));
    }
}

Answer 3

我最终绊倒了一个开源Java上传器小程序,并在其代码中找到了我需要知道的一切.以下是描述它的博客文章的链接以及来源:

文章
源代码

Answer 4

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,而是修改它transferred=len; 这是写入输出流的实际字节数的长度.当我计算添加的总字节数时,它等于ContentLength返回的实际值CountingMultiPartEntity.this.getContentLength();

public void write(byte[] b, int off, int len) throws IOException {
    wrappedOutputStream_.write(b,off,len);
    transferred=len;
    listener_.transferred(transferred);
}