HttpClient实现文件上传功能

以下是关于HttpClient实现文件上传功能的完整攻略。

简介

HttpClient是Apache的一个开源组件，它提供了高效的、简单的、简洁的编程接口，用于发送HTTP/HTTPS请求并处理响应。支持字符集转换、错误处理、重试处理、SSL连接、连接池等。

文件上传是HTTP协议中常用的一个功能，在web开发中尤为常见。HttpClient提供了完整的封装，以方便开发人员实现和管理文件上传。

实现

1. 添加HttpClient依赖

<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
</dependency>

1. 实现文件上传

以下是一个简单的文件上传示例:

import java.io.File;
import java.io.IOException;
import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

public class FileUploader {

    public static void main(String[] args) throws IOException {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost("http://localhost:8080/upload");
        //设置文件
        File file = new File("test.txt");
        HttpEntity entity = MultipartEntityBuilder
            .create()
            .addBinaryBody("file", file, ContentType.DEFAULT_BINARY, file.getName())
            .build();
        httpPost.setEntity(entity);
        CloseableHttpResponse response = httpClient.execute(httpPost);
        response.close();
        httpClient.close();
    }
}

以上示例中，通过创建CloseableHttpClient对象并使用HttpPost对象发起POST请求。使用MultipartEntityBuilder构建multipart/form-data类型的请求内容。其中包含一个名为"file"的文件参数，参数值为一个File对象。需要通过ContentType.DEFAULT_BINARY指定参数值类型，并设置文件名为file.getName()。

示例1：Spring MVC上传文件

以Spring MVC为例，实现文件上传的过程如下：

1. 添加依赖

添加Spring MVC和Apache Commons FileUpload依赖即可。

<!-- https://mvnrepository.com/artifact/org.springframework/spring-webmvc -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.3.3</version>
</dependency>

<!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
<dependency>
    <groupId>commons-fileupload</groupId>
    <artifactId>commons-fileupload</artifactId>
    <version>1.4</version>
</dependency>

1. 配置文件上传解析器

在Spring MVC配置文件中添加如下配置:

<bean id="multipartResolver"
      class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
    <property name="maxUploadSize" value="10485760"/> <!--设置最大上传大小为10M-->
    <property name="defaultEncoding" value="UTF-8"/> <!--设置默认编码-->
</bean>

1. 实现Controller

import java.io.File;
import java.io.IOException;
import java.util.List;
import org.apache.commons.io.FileUtils;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.MultipartHttpServletRequest;

@Controller
public class FileUploadController {

    @RequestMapping(value = "/upload", method = RequestMethod.POST)
    public String handleFileUpload(MultipartHttpServletRequest request, Model model) throws IOException {
        List<MultipartFile> files = request.getFiles("file");
        for (MultipartFile file : files) {
            File dest = new File("/path/to/destination/" + file.getOriginalFilename());
            FileUtils.copyInputStreamToFile(file.getInputStream(), dest);
        }
        model.addAttribute("result", "success");
        return "uploadResultPage";
    }
}

以上示例中，在Controller接收请求中使用了MultipartHttpServletRequest和MultipartFile，MultipartFile中即为文件上传的内容。将其保存到对应路径即可。

示例2：使用HttpClient模拟POST上传请求

以下是一个使用HttpClient模拟POST上传请求的示例：

import java.io.File;
import java.io.IOException;
import org.apache.commons.io.FileUtils;
import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

public class UploadFileTest {

    public static void main(String[] args) throws IOException {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpPost httppost = new HttpPost("http://localhost:8080/upload");
            File file = new File("D:\\test.docx");
            MultipartEntityBuilder builder = MultipartEntityBuilder.create();
            builder.addBinaryBody("file", file, ContentType.APPLICATION_OCTET_STREAM, file.getName());
            HttpEntity reqEntity = builder.build();
            httppost.setEntity(reqEntity);
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                System.out.println(response.getStatusLine());
                HttpEntity resEntity = response.getEntity();
                if (resEntity != null) {
                    System.out.println("Response content length: " + resEntity.getContentLength());
                }
                EntityUtils.consume(resEntity);
            } finally {
                response.close();
            }
        } finally {
            httpclient.close();
        }
    }
}

以上示例中，构造了一个HttpPost请求，其中设置了请求URL和需要上传的文件。使用MultipartEntityBuilder构建multipart/form-data类型的请求内容。其中包含一个名为"file"的文件参数，参数值为一个File对象。需要通过ContentType.APPLICATION_OCTET_STREAM指定参数值类型，并设置文件名为file.getName()。然后将构建好的请求内容设置到HttpPost实例中。

总结

以上是关于使用HttpClient实现文件上传功能的完整攻略。可以看出，通过HttpClient实现文件上传的过程主要是构建multipart/form-data类型的请求内容，并发送到服务器。在实际开发中，可根据具体需求进行配置和调整。