使用HttpClient实现文件的上传下载方法

下面我将详细讲解使用HttpClient实现文件上传下载方法的完整攻略。

一、引入HttpClient依赖

1. 在maven中添加HttpClient依赖

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.11</version>
</dependency>

1. 下载HttpClient的jar包，加入项目依赖中。

二、文件上传

1. 创建HttpClient

CloseableHttpClient httpClient = HttpClients.createDefault();

1. 创建Post请求

HttpPost httpPost = new HttpPost(url);

1. 创建MultipartEntityBuilder对象

MultipartEntityBuilder builder = MultipartEntityBuilder.create();

1. 设置参数和文件

builder.setCharset(Charset.defaultCharset());
builder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
builder.addBinaryBody("file", file);
builder.addTextBody("params", params);

1. 构建HttpEntity对象

HttpEntity entity = builder.build();
httpPost.setEntity(entity);

1. 执行请求

CloseableHttpResponse response = httpClient.execute(httpPost);

完整示例代码：

    public static void uploadFile(String url, File file, String params) throws IOException {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost(url);

        MultipartEntityBuilder builder = MultipartEntityBuilder.create();
        builder.setCharset(Charset.defaultCharset());
        builder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
        builder.addBinaryBody("file", file);
        builder.addTextBody("params", params);

        HttpEntity entity = builder.build();
        httpPost.setEntity(entity);

        CloseableHttpResponse response = httpClient.execute(httpPost);

        if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
            System.out.println("上传成功");
        } else {
            System.out.println("上传失败");
        }

        response.close();
        httpClient.close();
    }

三、文件下载

1. 创建HttpClient

CloseableHttpClient httpClient = HttpClients.createDefault();

1. 创建HttpGet请求

HttpGet httpGet = new HttpGet(url);

1. 执行请求

CloseableHttpResponse response = httpClient.execute(httpGet);

1. 读取response的数据

InputStream inputStream = response.getEntity().getContent();
byte[] bytes = new byte[1024];
int len;
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
while ((len = inputStream.read(bytes)) != -1) {
    byteArrayOutputStream.write(bytes, 0, len);
}
byte[] data = byteArrayOutputStream.toByteArray();

1. 将数据写入文件

FileOutputStream fileOutputStream = new FileOutputStream(file);
fileOutputStream.write(data);
fileOutputStream.flush();
fileOutputStream.close();

完整示例代码：

    public static void downloadFile(String url, File file) throws IOException {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet(url);

        CloseableHttpResponse response = httpClient.execute(httpGet);
        if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
            InputStream inputStream = response.getEntity().getContent();
            byte[] bytes = new byte[1024];
            int len;
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            while ((len = inputStream.read(bytes)) != -1) {
                byteArrayOutputStream.write(bytes, 0, len);
            }
            byte[] data = byteArrayOutputStream.toByteArray();
            FileOutputStream fileOutputStream = new FileOutputStream(file);
            fileOutputStream.write(data);
            fileOutputStream.flush();
            fileOutputStream.close();
        }

        response.close();
        httpClient.close();
    }

至此，使用HttpClient实现文件的上传下载方法的攻略讲解结束。