使用 Java 上传文件（带进度条）

file-io java upload progress-bar

2022-09-01 11:24:29

我对Java非常陌生，并且大部分时间都只是在自学，所以我已经开始构建一个小程序。我想制作一个可以从本地磁盘中选择一个文件并将其作为多部分/表单数据POST请求上传，但带有进度条。显然，用户必须向Java小程序授予访问硬盘驱动器的权限。现在我已经有了第一部分：用户可以使用对象选择文件，这可以方便地返回一个对象。但我想知道接下来会发生什么。我知道这将为我提供文件的总大小（以字节为单位），但是如何将所选内容发送到Web，以及如何监视已发送的字节数？提前致谢。JFileChooserFileFile.length()File

答案 1

若要使用 HttpClient 检查进度，请将 MultipartRequestEntity 包装在一个计算发送的字节数的实体周围。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);
        }
    }
}

然后实现一个进度列表，用于更新进度条。
请记住，进度条更新不得在事件调度线程上运行。

答案 2

更简单的计数实体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));
    }
}