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I have a web application that serves files for viewing. If it's a PDF, I simply attach it to an <object> element. However, the app supports serving word, excel, and powerpoint files. I have tried looking for ways to preview them online, but apparently we do not have the proper technology for that (at least not natively in a browser). So instead, I want the user to download the file to view locally.

The front-end is built with React and the back-end with Spring Boot. Currently, all static resources that are documents (PDF's, docs, spreadsheets, etc.) are served under the "/document-files/**" ant-matcher. Additionally, these resources can only be viewed privately, meaning that you have to be logged in to the application to view them. Here's how part of my SecurityConfig file looks like:

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
    String documentRootPath = "file:" + this.documentRootPath;
    registry.addResourceHandler("/resources/**").addResourceLocations("resources/");
    registry.addResourceHandler("/document-files/**").addResourceLocations(documentRootPath);
}

@Override
public void configure(HttpSecurity http) throws Exception {
    http.authorizeRequests() // ant matchers below are api routes and the baseUri for serving documents
        .antMatchers("/clients/**", "/projects/**", "/documents/**", "/document-files/**").authenticated()
        .anyRequest().permitAll() //... additional method chaining omitted for brevity
}

The problem is apparently just on the front end. I don't think it has anything to do with the configuration, but I posted it for reference. With this configuration I can download and preview PDF files just fine, using <object> but for all other files, the file does not load, so in <object> I add a link to open the file like so:

render() {
// some code omitted for brevity
    return (
        <Module>
            {!this.state.currDoc ? (
                <ul className={this.state.displayType}>{list}</ul>
            ) : (
                <object
                data={"/document-files" + this.state.filePath} 
                type={this.mimeTypes[document.fileType]}
                title={"Current Document: " + document.description + "." + document.fileType.toLowerCase()}>
                    {document.fileType === "PDF" ? "File could not be loaded!" : <div id="download-prompt">This file cannot be previewed online, click below to download and open locally.<a href={"http://localhost:3000/document-files" + this.state.filePath} download>Open</a></div>}
                </object>
            )}
        </Module>
    );
}

Upon clicking, the "save as" dialog box appears with the file name populated and the correct mime type but once I hit save, Chrome displays "Failed - No File". I have tried writing the href with and without the hostname. I've also tried removing the download attribute, but it redirects the page back to itself. I've even tried onLoad attribute on <object> but apparently that only works for images. I checked the network tab on dev tools and there is no record of the file being downloaded, unlike PDFs where the request is noted down.

How can I make non-PDF files download correctly using this setup?

score 0 · Answer 1 · answered May 24 '18 at 21:49

Thanks to javilobo8's GitHubGist, I found a way to download files using Axios, which library I was already using in my app to begin with. For quick reference, here is his code:

axios({
    url: 'http://localhost:5000/static/example.xlsx',
    method: 'GET',
    responseType: 'blob', // important
}).then((response) => {
    const url = window.URL.createObjectURL(new Blob([response.data]));
    const link = document.createElement('a');
    link.href = url;
    link.setAttribute('download', 'file.pdf');
    document.body.appendChild(link);
    link.click();
});

Also, there's multiple ways to work with Blobs, depending on if you're in IE, a browser that supports HTML5's Blob object, or another browser. This question helps split the code in 3 ways to form the dataUri for downloading raw data. After setting up my <a> tag, I just trigger the click event and the non-PDF file downloads!

1 Answers1