Java Http多次请求复用同一连接示例详解

@Slf4j
public class SinaPicDownload {
    /* 微博上某个画师的作品 */
    static final String HTTP_URL = "https://wx3.sinaimg.cn/mw2000/006jQ3i8ly1h5k50zujydj35k0334kjo.jpg";
    /* 下载之后放在颜如玉电脑的io文件下 */
    static final String LOCAL = "/Users/admin/io/灵魂莲华-皎月.jpeg";
    public static void main(String[] args) {
        try (
            InputStream in = new URL(HTTP_URL).openStream();
            FileOutputStream out = new FileOutputStream(LOCAL)
        ) {
            byte[] buffer = new byte[1024 << 2];
            int read;
            while ((read = in.read(buffer)) > -1) {
                out.write(buffer, 0, read);
            }
            out.flush();
        } 
        catch (Throwable e) {
            log.error("获取HTTP资源失败:", e);
        }
    }
}

@Slf4j
public class ReusableHttp {
    /* 颜如玉公司的OSS服务域名 */
    static final String HOST = "****.oss-cn-zhangjiakou.aliyuncs.com";
    static final int PORT = 80;
    /* 颜如玉在OSS上放置的几个资源 */
    static final String[] URLS = new String[]{
        "/context/reusable/gtyj.text",
        "/context/reusable/tlyxqch.text",
        "/context/reusable/yj.text",
        "/context/reusable/ls.text"
    };
    /* CR = '\r'; LF = '\n'*/
    static final byte[] CRLF = new byte[]{Chars.CR, Chars.LF};
    static final String LOCAL_PATH = "/Users/admin/io/";
}

public static void main(String[] args) {
    try {
        try (
            Socket socket = new Socket(HOST, PORT);
            OutputStream out = socket.getOutputStream();
            InputStream in = socket.getInputStream()
        ) {
            /* 复用连接,获取资源 */
            reusable(out, in);
        }
    }
    catch (IOException e) {
        log.error("请求出现异常", e);
    }
}

/**
 * Write Request Line
 *
 * RequestLine encoding规范
 *
 * **********************************************
 * * method * sp * URL * sp * version * cr * lf *
 * **********************************************
 */
static void writeRequestLine(OutputStream out, String url) throws IOException {
    /* 注意空格一定要按照规定来摆放 */
    out.write(("GET " + url + " HTTP/1.1").getBytes());
    /* 最后再写入一个回车、换行符表示Request Line结束 */
    out.write(CRLF);
}

/**
 * Write Request Header
 *
 * HeaderLine encoding规范
 *
 * *******************************************
 * * header field name * : * value * cr * lf *
 * *******************************************
 * ....
 * *******************************************
 * * header field name * : * value * cr * lf *
 * *******************************************
 * ...
 * ***********
 * * cr * lf *
 * ***********
 * ***************
 * * Entity Body *
 * ***************
 */
static void writeHeaderLine(OutputStream out) throws IOException {
    out.write("Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9".getBytes());
    out.write(CRLF);
    out.write("Accept-Encoding: gzip, deflate".getBytes());
    out.write(CRLF);
    out.write("Accept-Language: zh-CN,zh;q=0.9".getBytes());
    out.write(CRLF);
    out.write("Connection: keep-alive".getBytes());
    out.write(CRLF);
    out.write("Host: kuaimai-sheji.oss-cn-zhangjiakou.aliyuncs.com".getBytes());
    out.write(CRLF);
    /* 最后再写入一个回车、换行符表示Request Header结束 */
    out.write(CRLF);
}

/**
 * 1.向Server端写出请求
 * 2.接受Server端回复
 * 3.写到颜如玉本地机器的io文件夹下
 *
 * @param out 往Server端写出流
 * @param in  Server端往Client端写入流
 */
static void reusable(OutputStream out, InputStream in) throws IOException {
    for (int i = 0, s = URLS.length; i < s; i++) {
        writeRequestLine(out, URLS[i]);
        writeHeaderLine(out);
        out.flush();
        byte[] bytes = new byte[512];
        in.read(bytes);
        String file = LOCAL_PATH + i + ".text";
        try (
            FileOutputStream fo = new FileOutputStream(file)
        ) {
            fo.write(bytes);
            fo.flush();
        }
        catch (Throwable e) {
            log.error("文件写入出现异常", e);
        }
    }
}