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Java API development practice: How to implement the file upload function simply and practically?

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Jun 18, 2023 pm 07:27 PM

java File Upload api

Java API development practice: How to implement the file upload function simply and practically?

In modern applications, many business scenarios require uploading resources such as files or pictures. As a programming language widely used in back-end development, Java's powerful API provides developers with a lot of convenience. In this article, we will introduce how to use Java API to implement file upload function.

1. Overview of file upload

File upload refers to uploading local files or data obtained from other applications to the server, usually implemented by a website or web application. File upload is an important part of network applications. Common scenarios include but are not limited to:

Users upload avatars or other pictures
System administrators upload data backup files
File sharing, file expansion, etc.

Whether it is front-end or back-end development, the file upload function is a common skill that needs to be mastered. For the file upload function, Java provides a variety of implementation methods, such as common Servlet, FileUpload, etc. We will introduce one of the simpler methods in the following two parts.

2. Java API file upload implementation steps

In this example, we will use Apache Commons FileUpload to implement file upload. This API library was developed by Apache and can help Java developers easily implement file upload functions without having to understand the details of the HTTP protocol in depth.

The following are the steps to use this library:

Integrate Apache Commons FileUpload

First, we need to introduce Apache Commons FileUpload in the pom.xml file Dependency, in the Maven project, you can add the following code to the pom.xml file:
```
<dependency>
    <groupId>commons-fileupload</groupId>
    <artifactId>commons-fileupload</artifactId>
    <version>1.3.3</version>
</dependency>
```
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Create Servlet

Next, you need to create a Servlet class. The role of the Servlet class is to receive file upload requests sent by the client, and parse and save the data locally on the server. The code is implemented as follows:

@WebServlet(name = "FileUploadServlet", urlPatterns = "/upload")
public class FileUploadServlet extends HttpServlet {

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

        String uploadPath = "上传文件的本地路径"; // 上传文件保存地地方
        //创建文件上传的实例
        DiskFileItemFactory factory = new DiskFileItemFactory();
        factory.setRepository(new File(uploadPath));
        ServletFileUpload upload = new ServletFileUpload(factory);
        upload.setHeaderEncoding("UTF-8");

        try {
            List<FileItem> items = upload.parseRequest(request);
            for(FileItem item : items){
                if(!item.isFormField()){
                    String fileName = item.getName();//获取上传文件的名字
                    String filePath = uploadPath + File.separator + fileName;//获取上传文件的存储路径   
                    File uploadedFile = new File(filePath);
                    item.write(uploadedFile);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

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Create a front-end page

Finally, you need to create a front-end page for uploading files. There is a form on the page through which users can select files and then upload the files.

<html>
<head>
    <title>File Upload with Servlet</title>        
</head>
<body>
    <form action="/upload" method="post" enctype="multipart/form-data">
    <div>
            <input type="file" name="file" />
        </div>
        <div>
            <input type="submit" value="Upload File" />
        </div>
    </form>
</body>
</html>

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4. Summary

The above is a simple practice on how to use Java API to implement the file upload function. With Apache Commons FileUpload, Java developers can easily implement file upload functionality in web applications without having to deal with the details of HTTP requests. I hope this article can help you understand the implementation process of file upload and improve your development efficiency.

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