【Qt】Qt Http 下载（转载）

QT之HTTP请求下载

标签： Qt HTTP

简述

最近在研究了一下用Qt 的方法来实现http下载，Qt 中的Http请求主要用到了QNetworkAccessManager、QNetworkReply、QNetworkRequest 这三块。本篇文章主要叙述如何用Qt 的方法进行HTTP 请求下载文件，能够支持****断点续传****（断点续传即能够手动停止下载，下次可以从已经下载的部分开始继续下载未完成的部分，而没有必要从头开始上传下载），并且实时更新下载信息。整体代码考虑十分周到，对各种情况也做了相应的处理，并且有通俗易懂的注释。好了，代码走起！

代码之路

在讲解代码之前先看一下效果图：

效果：

从图中可以看出点击start按钮，进行下载，stop按钮暂停当前下载，close按钮停止当前下载，并删除已经下载的临时文件，并将所有参数重置， 这里界面中下载链接输入框为空是因为我在代码中默认了url，也可以在输入框中输入url进行下载。

---

代码主要包含两个部分：

1、DownLoadManager ： 用来请求下载，向界面传递下载信息，并将下载的内容保存到文件中

2、MyHttpDownload ： 用来接收下载链接，利用DownLoadManager进行下载，更新界面，并对当前下载进行操作（包括：开始、暂停、停止下载）。

1、DOWNLOADMANAGER

#include "downloadmanager.h"
#include <QFile>
#include <QDebug>
#include <QFileInfo>
#include <QDir>
 
#define DOWNLOAD_FILE_SUFFIX    "_tmp"
 
DownLoadManager::DownLoadManager(QObject *parent)
    : QObject(parent)
    , m_networkManager(NULL)
    , m_url(QUrl(""))
    , m_fileName("")
    , m_isSupportBreakPoint(false)
    , m_bytesReceived(0)
    , m_bytesTotal(0)
    , m_bytesCurrentReceived(0)
    , m_isStop(true)
{
    m_networkManager = new QNetworkAccessManager(this);
}
 
DownLoadManager::~DownLoadManager()
{}
 
// 设置是否支持断点续传;
void DownLoadManager::setDownInto(bool isSupportBreakPoint)
{
    m_isSupportBreakPoint = isSupportBreakPoint;
}
 
// 获取当前下载链接;
QString DownLoadManager::getDownloadUrl()
{
    return m_url.toString();
}
 
// 开始下载文件，传入下载链接和文件的路径;
void DownLoadManager::downloadFile(QString url , QString fileName)
{
    // 防止多次点击开始下载按钮，进行多次下载，只有在停止标志变量为true时才进行下载;
    if (m_isStop)
    {
        m_isStop = false;
        m_url = QUrl(url);
 
        // 这里可用从url中获取文件名，但不是对所有的url都有效;
//      QString fileName = m_url.fileName();
 
        // 将当前文件名设置为临时文件名，下载完成时修改回来;
        m_fileName = fileName + DOWNLOAD_FILE_SUFFIX;
 
        // 如果当前下载的字节数为0那么说明未下载过或者重新下载
        // 则需要检测本地是否存在之前下载的临时文件，如果有则删除
        if (m_bytesCurrentReceived <= 0)
        {
            removeFile(m_fileName);
        }
 
        QNetworkRequest request;
        request.setUrl(m_url);
 
        // 如果支持断点续传，则设置请求头信息
        if (m_isSupportBreakPoint)
        {
            QString strRange = QString("bytes=%1-").arg(m_bytesCurrentReceived);
            request.setRawHeader("Range", strRange.toLatin1());
        }
 
        // 请求下载;
        m_reply = m_networkManager->get(request);
 
        connect(m_reply, SIGNAL(downloadProgress(qint64, qint64)), this, SLOT(onDownloadProgress(qint64, qint64)));
        connect(m_reply, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
        connect(m_reply, SIGNAL(finished()), this, SLOT(onFinished()));
        connect(m_reply, SIGNAL(error(QNetworkReply::NetworkError)), this, SLOT(onError(QNetworkReply::NetworkError)));
    }   
}
 
// 下载进度信息;
void DownLoadManager::onDownloadProgress(qint64 bytesReceived, qint64 bytesTotal)
{
    if (!m_isStop)
    {
        m_bytesReceived = bytesReceived;
        m_bytesTotal = bytesTotal;
        // 更新下载进度;(加上 m_bytesCurrentReceived 是为了断点续传时之前下载的字节)
        emit signalDownloadProcess(m_bytesReceived + m_bytesCurrentReceived, m_bytesTotal + m_bytesCurrentReceived);
    }   
}
 
// 获取下载内容，保存到文件中;
void DownLoadManager::onReadyRead()
{
    if (!m_isStop)
    {
        QFile file(m_fileName);
        if (file.open(QIODevice::WriteOnly | QIODevice::Append))
        {
            file.write(m_reply->readAll());
        }
        file.close();
    }   
}
 
// 下载完成;
void DownLoadManager::onFinished()
{
    m_isStop = true;
    // http请求状态码;
    QVariant statusCode = m_reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
 
    if (m_reply->error() == QNetworkReply::NoError)
    {
        // 重命名临时文件;
        QFileInfo fileInfo(m_fileName);
        if (fileInfo.exists())
        {
            int index = m_fileName.lastIndexOf(DOWNLOAD_FILE_SUFFIX);
            QString realName = m_fileName.left(index);
            QFile::rename(m_fileName, realName);
        }
    }
    else
    {
        // 有错误输出错误;
        QString strError = m_reply->errorString();
        qDebug() << "__________" + strError;
    }
 
    emit signalReplyFinished(statusCode.toInt());
}
 
// 下载过程中出现错误，关闭下载，并上报错误，这里未上报错误类型，可自己定义进行上报;
void DownLoadManager::onError(QNetworkReply::NetworkError code)
{
    QString strError = m_reply->errorString();
    qDebug() << "__________" + strError;
 
    closeDownload();
    emit signalDownloadError();
}
 
// 停止下载工作;
void DownLoadManager::stopWork()
{
    m_isStop = true;
    if (m_reply != NULL)
    {
        disconnect(m_reply, SIGNAL(downloadProgress(qint64, qint64)), this, SLOT(onDownloadProgress(qint64, qint64)));
        disconnect(m_reply, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
        disconnect(m_reply, SIGNAL(finished()), this, SLOT(onFinished()));
        disconnect(m_reply, SIGNAL(error(QNetworkReply::NetworkError)), this, SLOT(onError(QNetworkReply::NetworkError)));
        m_reply->abort();
        m_reply->deleteLater();
        m_reply = NULL;
    }
}
 
// 暂停下载按钮被按下,暂停当前下载;
void DownLoadManager::stopDownload()
{
    // 这里m_isStop变量为了保护多次点击暂停下载按钮，导致m_bytesCurrentReceived 被不停累加;
    if (!m_isStop)
    {
        //记录当前已经下载字节数
        m_bytesCurrentReceived += m_bytesReceived;
        stopWork();
    }   
}
 
// 重置参数;
void DownLoadManager::reset()
{
    m_bytesCurrentReceived = 0;
    m_bytesReceived = 0;
    m_bytesTotal = 0;
}
 
// 删除文件;
void DownLoadManager::removeFile(QString fileName)
{
    // 删除已下载的临时文件;
    QFileInfo fileInfo(fileName);
    if (fileInfo.exists())
    {
        QFile::remove(fileName);
    }
}
 
// 停止下载按钮被按下，关闭下载，重置参数，并删除下载的临时文件;
void DownLoadManager::closeDownload()
{
    stopWork();
    reset();
    removeFile(m_fileName);
}

2、MYHTTPDOWNLOAD

#include "myhttpdownload.h"
#include "downloadmanager.h"
#include <QDebug>
 
#define UNIT_KB 1024            //KB
#define UNIT_MB 1024*1024       //MB
#define UNIT_GB 1024*1024*1024  //GB
 
#define TIME_INTERVAL 300       //0.3s
 
MyHttpDownload::MyHttpDownload(QWidget *parent)
    : QWidget(parent)
    , m_downloadManager(NULL)
    , m_url("")
    , m_timeInterval(0)
    , m_currentDownload(0)
    , m_intervalDownload(0)
{
    ui.setupUi(this);
    initWindow();
}
 
MyHttpDownload::~MyHttpDownload()
{
 
}
 
void MyHttpDownload::initWindow()
{
    ui.progressBar->setValue(0);
    connect(ui.pButtonStart, SIGNAL(clicked()), this, SLOT(onStartDownload()));
    connect(ui.pButtonStop, SIGNAL(clicked()), this, SLOT(onStopDownload()));
    connect(ui.pButtonClose, SIGNAL(clicked()), this, SLOT(onCloseDownload()));
    // 进度条设置样式;
    ui.progressBar->setStyleSheet("\
                QProgressBar\
                {\
                    border-width: 0 10 0 10;\
                    border-left: 1px, gray;\
                    border-right: 1px, gray;\
                    border-image:url(:/Resources/progressbar_back.png);\
                }\
                QProgressBar::chunk\
                {\
                    border-width: 0 10 0 10;\
                    border-image:url(:/Resources/progressbar.png);\
                }");
}
 
// 开始下载;
void MyHttpDownload::onStartDownload()
{
    // 从界面获取下载链接;
    m_url = ui.downloadUrl->text();
    if (m_downloadManager == NULL)
    {
        m_downloadManager = new DownLoadManager(this);
        connect(m_downloadManager , SIGNAL(signalDownloadProcess(qint64, qint64)), this, SLOT(onDownloadProcess(qint64, qint64)));
        connect(m_downloadManager, SIGNAL(signalReplyFinished(int)), this, SLOT(onReplyFinished(int)));
    }
 
    // 这里先获取到m_downloadManager中的url与当前的m_url 对比，如果url变了需要重置参数,防止文件下载不全;
    QString url = m_downloadManager->getDownloadUrl();
    if (url != m_url)
    {
        m_downloadManager->reset();
    }
    m_downloadManager->setDownInto(true);
    m_downloadManager->downloadFile(m_url, "F:/MyHttpDownload/MyDownloadFile.zip");
    m_timeRecord.start();
    m_timeInterval = 0;
    ui.labelStatus->setText(QStringLiteral("正在下载"));
}
 
// 暂停下载;
void MyHttpDownload::onStopDownload()
{
    ui.labelStatus->setText(QStringLiteral("停止下载"));
    if (m_downloadManager != NULL)
    {
        m_downloadManager->stopDownload();
    }
    ui.labelSpeed->setText("0 KB/S");
    ui.labelRemainTime->setText("0s");
}
 
// 关闭下载;
void MyHttpDownload::onCloseDownload()
{
    m_downloadManager->closeDownload();
    ui.progressBar->setValue(0);
    ui.labelSpeed->setText("0 KB/S");
    ui.labelRemainTime->setText("0s");
    ui.labelStatus->setText(QStringLiteral("关闭下载"));
    ui.labelCurrentDownload->setText("0 B");
    ui.labelFileSize->setText("0 B");
}
 
// 更新下载进度;
void MyHttpDownload::onDownloadProcess(qint64 bytesReceived, qint64 bytesTotal)
{
    // 输出当前下载进度;
    // 用到除法需要注意除0错误;
    qDebug() << QString("%1").arg(bytesReceived * 100 / bytesTotal + 1);
    // 更新进度条;
    ui.progressBar->setMaximum(bytesTotal);
    ui.progressBar->setValue(bytesReceived);
 
    // m_intervalDownload 为下次计算速度之前的下载字节数;
    m_intervalDownload += bytesReceived - m_currentDownload;
    m_currentDownload = bytesReceived;
 
    uint timeNow = m_timeRecord.elapsed();
 
    // 超过0.3s更新计算一次速度;
    if (timeNow - m_timeInterval > TIME_INTERVAL)
    {
        qint64 ispeed = m_intervalDownload * 1000 / (timeNow - m_timeInterval);
        QString strSpeed = transformUnit(ispeed, true);
        ui.labelSpeed->setText(strSpeed);
        // 剩余时间;
        qint64 timeRemain = (bytesTotal - bytesReceived) / ispeed;
        ui.labelRemainTime->setText(transformTime(timeRemain));
 
        ui.labelCurrentDownload->setText(transformUnit(m_currentDownload));
        ui.labelFileSize->setText(transformUnit(bytesTotal));
 
        m_intervalDownload = 0;
        m_timeInterval = timeNow;
    }
}
 
// 下载完成;
void MyHttpDownload::onReplyFinished(int statusCode)
{
    // 根据状态码判断当前下载是否出错;
    if (statusCode >= 200 && statusCode < 400)
    {
        qDebug() << "Download Failed";
    }
    else
    {
        qDebug() << "Download Success";
    }
}
 
// 转换单位;
QString MyHttpDownload::transformUnit(qint64 bytes , bool isSpeed)
{
    QString strUnit = " B";
    if (bytes <= 0)
    {
        bytes = 0;
    }
    else if (bytes < UNIT_KB)
    {
    }
    else if (bytes < UNIT_MB)
    {
        bytes /= UNIT_KB;
        strUnit = " KB";
    }
    else if (bytes < UNIT_GB)
    {
        bytes /= UNIT_MB;
        strUnit = " MB";
    }
    else if (bytes > UNIT_GB)
    {
        bytes /= UNIT_GB;
        strUnit = " GB";
    }
 
    if (isSpeed)
    {
        strUnit += "/S";
    }
    return QString("%1%2").arg(bytes).arg(strUnit);
}
 
// 转换时间;
QString MyHttpDownload::transformTime(qint64 seconds)
{
    QString strValue;
    QString strSpacing(" ");
    if (seconds <= 0)
    {
        strValue = QString("%1s").arg(0);
    }
    else if (seconds < 60)
    {
        strValue = QString("%1s").arg(seconds);
    }
    else if (seconds < 60 * 60)
    {
        int nMinute = seconds / 60;
        int nSecond = seconds - nMinute * 60;
 
        strValue = QString("%1m").arg(nMinute);
 
        if (nSecond > 0)
            strValue += strSpacing + QString("%1s").arg(nSecond);
    }
    else if (seconds < 60 * 60 * 24)
    {
        int nHour = seconds / (60 * 60);
        int nMinute = (seconds - nHour * 60 * 60) / 60;
        int nSecond = seconds - nHour * 60 * 60 - nMinute * 60;
 
        strValue = QString("%1h").arg(nHour);
 
        if (nMinute > 0)
            strValue += strSpacing + QString("%1m").arg(nMinute);
 
        if (nSecond > 0)
            strValue += strSpacing + QString("%1s").arg(nSecond);
    }
    else
    {
        int nDay = seconds / (60 * 60 * 24);
        int nHour = (seconds - nDay * 60 * 60 * 24) / (60 * 60);
        int nMinute = (seconds - nDay * 60 * 60 * 24 - nHour * 60 * 60) / 60;
        int nSecond = seconds - nDay * 60 * 60 * 24 - nHour * 60 * 60 - nMinute * 60;
 
        strValue = QString("%1d").arg(nDay);
 
        if (nHour > 0)
            strValue += strSpacing + QString("%1h").arg(nHour);
 
        if (nMinute > 0)
            strValue += strSpacing + QString("%1m").arg(nMinute);
 
        if (nSecond > 0)
            strValue += strSpacing + QString("%1s").arg(nSecond);
    }
 
    return strValue;
}

标注： 代码注释中提到可以根据URL来获取文件名，下方给予解释说明。

QString QUrl::fileName(ComponentFormattingOptions options = FullyDecoded) const
Returns the name of the file, excluding the directory path.
Note that, if this QUrl object is given a path ending in a slash, the name of the file is considered empty.
If the path doesn’t contain any slash, it is fully returned as the fileName.

在Qt助手中我们找到此方法，根据加粗的字段可以看出fileName()方法也可能返回为空，所以不是都有效。