自己尝试使用Tomcat配合idea，写了段web代码，提供一个文件供Android客户端进行下载

1. OkHttp下载文件

更新下载进度

OkHttp，真心好用，很强大

Activity代码：

public class DownActivity extends AppCompatActivity implements DownCallback<Integer> {
    private ProgressBar progressBar;
    private Platform mPlatform;
    private String directoryPath;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_down);
        mPlatform = Platform.get();
        init();
    }

    /**
     * 初始化
     */
    private void init() {
        Button button = (Button) findViewById(R.id.down_activity_bt);
        progressBar = (ProgressBar) findViewById(R.id.down_activity_pb);
        String path = Environment.getExternalStorageDirectory().getPath() + File.separator + Strings.FILE_PATH;
        File directory = new File(path);
        if (!directory.exists()) {
            boolean b = directory.mkdirs();
            if (b) ToastUtils.show(DownActivity.this, "文件夹创建成功");
        }
        directoryPath = directory.getPath();
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                down();
            }
        });
    }

    /**
     * 下载请求
     */
    private void down() {
        OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .connectTimeout(10, TimeUnit.SECONDS)
                .build();
        Request request = new Request.Builder()
                .url(Urls.DOWN_URL)
                .build();
        Call call = okHttpClient.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                sendFailResultCallback(e);
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                ResponseBody responseBody = null;
                BufferedInputStream bis = null;
                FileOutputStream fos = null;
                try {
                    if (call.isCanceled()) {
                        sendFailResultCallback(new IOException("Request Canceled"));
                        return;
                    }
                    if (response.isSuccessful()) {
                        responseBody = response.body();
                        long total = responseBody.contentLength();
                        bis = new BufferedInputStream(responseBody.byteStream());
                        File file = new File(directoryPath, Strings.FILE_NAME);
                        fos = new FileOutputStream(file);
                        byte[] bytes = new byte[1024 * 8];
                        int len;
                        long current = 0;
                        while ((len = bis.read(bytes)) != -1) {
                            fos.write(bytes, 0, len);
                            fos.flush();
                            current += len;
                            //计算进度
                            int progress = (int) (100 * current / total);
                            onProgress(progress);
                        }
                    } else {
                        sendFailResultCallback(new IOException("Request Failed"));
                    }
                } catch (Exception e) {
                    sendFailResultCallback(e);
                } finally {
                    if (null != responseBody) {
                        responseBody.close();
                    }
                    CloseIO.close(bis);
                    CloseIO.close(fos);
                }
            }
        });
    }

    /**
     * 下载失败
     */
    @Override
    public void sendFailResultCallback(final Exception e) {
        doSomething(new Runnable() {
            @Override
            public void run() {
                String info = "Fail Message --> " + e.getMessage();
                ToastUtils.show(DownActivity.this, info);
            }
        });


    }

    /**
     *  更新下载进度
     */
    @Override
    public void onProgress(final Integer integer) {
        doSomething(new Runnable() {
            @Override
            public void run() {
                progressBar.setProgress(integer);
            }
        });

    }

    private void doSomething(Runnable runnable) {
        mPlatform.execute(runnable);
    }
}

当成功之后，利用responseBody.byteStream()得到一个InputStream,之后，只需要使用IO流将请求到的数据写入到指定的文件就可以

2. Idea web应用

创建一个Maven项目

2.1 Pom.xml 配置文件

添加必有库:

    <packaging>war</packaging>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <kotlin.version>1.0.5</kotlin.version>
    </properties>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.0</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.19.1</version>
            </plugin>
           
        </plugins>
    </build>
    <dependencies>
        <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/javax.servlet.jsp/jsp-api -->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.2</version>
            <scope>provided</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/javax.servlet/jstl -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
            <scope>runtime</scope>
        </dependency>
    </dependencies>

2.2 在main中添加webapp

添加webapp

web.xml文件:

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
            http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0">
    <display-name>jerk</display-name>
    
</web-app>

2.3 Tomcat配置

• 在Add New Configuration中，添加Tomcat Server
  

  Tomcat配置

• 在Server中的Application server中添加本地Tomcat路径

• 在Deloyment中添加项目的导出方式为war，并将Application Context设置为项目名称
  

  Deloyment

• 在Server中，修改On Update action为Redeploy，On frame deactivation为Up resources

2.4 Servlet业务代码

public class DownServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("Content-Disposition", "attachment;filename=a.mp4");
        String path = "/Users/g&c/Movies/17线性表12.mp4";
        File file = new File(path);
        long total = file.length();
        resp.setContentLengthLong(total);
        ServletOutputStream outputStream = resp.getOutputStream();
        FileInputStream fis = new FileInputStream(file);
        byte[] bytes = new byte[1024 * 8];
        int len;
        while ((len = fis.read(bytes)) != -1) {
            outputStream.write(bytes, 0, len);
        }
        fis.close();
     }
}

doGet()方法就是get请求调用的，里面读取本地文件然后输出文件流

2.5 补充web.xml

在web.xml中添加：

    <servlet>
        <servlet-name>android</servlet-name>
        <servlet-class>download.DownServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>android</servlet-name>
        <url-pattern>/download</url-pattern>
    </servlet-mapping>

<servlet-name>中的android为随意写的名字

完整的项目请求地址：http://192.168.0.113:8080/jerk/download

个人ip地址+端口号+/项目名+/url-pattern

3. 最后

有错误请指出

共勉 ：）