如何實現檔案傳輸?

使用http來實現
Content-Type:application/x-www-form-urlencoded ==> 請求體為經過url編碼的字串
Content-Type:multipart/form-data ==> 請求體二進位制資料,並以邊界boundary來分割field,每一個可以設定下一級的資料型別Content-Type;

http資訊傳輸方式在form中的實現
設定form的屬性ENCTYPE=”application/x-www-form-urlencoded”(預設)
設定form的屬性ENCTYPE=”multipart/form-data” ==> form裡面的input的值以2進位制的方式傳過去.

測試,使用servlet實現http的檔案傳輸功能

總結:
1. HttpServlet提供了getParameter(arg)的方式接受字串
2. HttpServlet使用流的形式接受位元組資料,但是接收的資料相當原始,接收整個requestBody,想要獲取我們的目標資訊,我們還需要進一步處理
3. 但是,自己寫一段程式碼去處理太麻煩,懶,於是去找別人造過的輪子common-fileupload.jar;common-io.jar

//下面為程式碼實現
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws
 
 ServletException, IOException {
    InputStream inputStream = request.getInputStream();
    int len = 0;
    byte[] b = new byte[1024];
    while((len=inputStream.read(b))!=-1){
        System.out.println(new String(b,0,len));
    }

    inputStream.close();
    /*
    ------WebKitFormBoundaryr8YA5CmD7qBdF7wa
    Content-Disposition: form-data; name="uploader"

    guang
    ------WebKitFormBoundaryr8YA5CmD7qBdF7wa
    Content-Disposition: form-data; name="file"; filename="筆記本.txt"
    Content-Type: text/plain

    # 筆記
    ## 2017-10-11 星期三
    ```
    2017-10-11 星期三
    ```
    ------WebKitFormBoundaryr8YA5CmD7qBdF7wa--
     * */
 

}


protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doGet(request, response);
}

common-fileupload實現http的檔案傳輸功能

總結:
1. 竊取人家的輪子就是美滋滋;具體用法看官網http://commons.apache.org/proper/commons-fileupload/index.html照著做就行了
2. 但是我還是覺得麻煩啊,既要看文件,自己還是要寫不少的程式碼,WTF



//下面為程式碼實現
public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

    /*
     * ServletFileUpload是common-fileupload.jar的核心類
     * */
    boolean isMultipartContent = ServletFileUpload.isMultipartContent(request);
    if (!isMultipartContent) {
        throw new RuntimeException("your form is not multipart/form-data");
    }
    DiskFileItemFactory factory = new DiskFileItemFactory();
    factory.setRepository(new File("f:\\"));
    ServletFileUpload sfu = new ServletFileUpload(factory);
    sfu.setHeaderEncoding("UTF-8");
    try {
        List<FileItem> fileItems = sfu.parseRequest(request);
        for (FileItem fileitem : fileItems) {
            if (fileitem.isFormField()) {
                processFormField(fileitem);
            } else {
                processUploadField(fileitem);
            }
        }
    } catch (FileUploadBase.FileSizeLimitExceededException e) {
        // throw new RuntimeException("");
    } catch (FileUploadBase.SizeLimitExceededException e) {
        //
    } catch (FileUploadException e) {
        e.printStackTrace();
    }
}

/**
 * 處理上傳檔案
 * */
private void processUploadField(FileItem fileitem) {
    try {
        //獲得輸入流
        InputStream inputStream = fileitem.getInputStream();
        String directoryRealPath = this.getServletContext().getRealPath("/WEB-INF/upload");
        File storeDirectory = new File(directoryRealPath);
        if (!storeDirectory.exists()) {
            storeDirectory.mkdirs();
        }
        //獲取並重構檔名
        String filename = fileitem.getName();   
        if (filename != null) {
            filename = FilenameUtils.getName(filename);
        }
        filename = UUID.randomUUID() + "_" + filename;
        //建立系統下的檔案以流的形式寫出
        File file = new File(storeDirectory, filename);
        FileOutputStream fileOutputStream = new FileOutputStream(file);
        int len = 0;
        byte[] b = new byte[1024];
        while((len=inputStream.read(b))!=-1){
            fileOutputStream.write(b, 0, len);
        }
        fileOutputStream.close();
        inputStream.close();

    } catch (IOException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

/**
 * 處理普通表單資訊
 * */
private void processFormField(FileItem fileitem) {
    try {
        String fieldname = fileitem.getFieldName();
        String fieldvalue = fileitem.getString("UTF-8");
        System.out.println(fieldname + "=" + fieldvalue);
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    }
}

public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
    doGet(request, response);
}



//下載檔案類似
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String path = this.getServletContext().getRealPath("/WEB-INF/upload/guang.jpg");
    FileInputStream fileInputStream = new FileInputStream(path);
    ServletOutputStream servletOutputStream = response.getOutputStream();
    String filename = path.substring(path.lastIndexOf("\\")+1);
    //根據http協議,設定響應頭的屬性,告知瀏覽器接受資訊的方式即可
    response.setHeader("content-disposition", "attachment;filename="+filename);
    response.setHeader("content-type","img/jpeg");
    int len = 0;
    byte[] b = new byte[1024];
    while((len=fileInputStream.read(b))!=-1){
        servletOutputStream.write(b, 0, len);
    }
    servletOutputStream.close();
    fileInputStream.close();
}

在struts2中實現檔案檔案傳輸功能

總結:
1. struts2底層使用的還是common-fileupload,in other words,struts2封裝了這個類庫,用起來更簡潔了;
2. 簡潔是簡潔了,但是程式碼格式變得呆呆的,被固定了,果然世界的真理是等價交換
3. struts2還利用了他的攔截器鏈對對上傳檔案進行了事前事後的收拾工作,
    舉個栗子:限制上傳檔案的大小,限制上傳檔案的字尾名,限制上傳檔案的型別etc.等等,在struts的配置檔案中把屬性配置上就行了,
    emm,大概這些功能在前端可以讓js做,但是我對js不太熟,emm,以後可以參考一些一些流行的js框架
    反正別自己跑去問requestHeader就對了,能簡單搞定那還是簡單點最好
4. 檔案下載沒做優化,還是搞一個流,設定響應頭的屬性,輸出流就ok了

//下面是程式碼實現
private File photo;//上傳的檔案欄位
private String photoFileName;//上傳的檔案的檔名,固定寫法:上傳的檔案欄位+FileName
private String photoContentType;//上傳的檔案的MIME型別,固定寫法:上傳的檔案的檔名+ContentType


public String upload(){

    ServletContext application = ServletActionContext.getServletContext();
    String filePath = application.getRealPath("/WEB-INF/uploadFile");
    File file = new File(filePath);
    if(!file.exists()){
        file.mkdirs();
    }
    photo.renameTo(new File(file,photoFileName));

    return null;
}

現在比較主流的SpringMVC又是怎麼實現的呢?

總結:
1. springMVC有兩種實現,一種和struts2一樣,整合common-upload.jar;另外一種則是使用了srevlet3自帶的上傳功能
2. 使用時,需要配置對應的實現類bean(CommonsMultipartResolver/StandardServletMultipartResolver),通過容器管理,從而在系統中應用