NET2Java之十：HTTP请求

在微服务化大行其道的今天，http请求也是极为常见的功能之一，.NET中有HttpWebRequest和HttpClient，那java中该如何发送Http请求呢？

原生请求

Java原生提供了HttpURLConnection来发送Http请求，示例如下：

public class HttpUtil {
    /**
     * 原生Get请求。
     *
     * @param getUrl
     * @return
     * @throws Exception
     */
    public static String sendGet(String getUrl) throws Exception {

        URL httpUrl = new URL(getUrl);
        HttpURLConnection httpConn = (HttpURLConnection) httpUrl.openConnection();
        httpConn.setRequestMethod(HttpMethod.GET.name());
        httpConn.setDoOutput(false); //标明是否从请求体发送数据到服务器
        httpConn.setDoInput(true); //标明是否期望接收返回值数据
        httpConn.setConnectTimeout(10); //10ms超时
        httpConn.setReadTimeout(100); //100ms超时

        //打开链接
        httpConn.connect();

        int statusCode = httpConn.getResponseCode();
        if (statusCode != 200) {
            System.out.println("请求出错！");
            return "";
        }
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        InputStream input = httpConn.getInputStream();
        byte[] buf = new byte[1024];
        int len = 0;
        while ((len = input.read(buf)) > 0) {
            output.write(buf, 0, len);
        }
        String httpReturn = output.toString("utf-8");
        output.close();
        input.close();
        httpConn.disconnect();
        return httpReturn;
    }

    /**
     * 原生Post请求。
     *
     * @param postUrl
     * @param postParams
     * @return
     * @throws Exception
     */
    public static String sendPost(String postUrl, String postParams, String contentType) throws Exception {

        URL httpUrl = new URL(postUrl);
        HttpURLConnection httpConn = (HttpURLConnection) httpUrl.openConnection();
        httpConn.setRequestMethod(HttpMethod.POST.name());
        httpConn.setRequestProperty("Content-Type", contentType); //请求头，比如application/json; utf-8
        httpConn.setRequestProperty("Accept", "application/json"); //返回值

        httpConn.setDoOutput(true);
        httpConn.setDoInput(true);

        DataOutputStream dos = new DataOutputStream(httpConn.getOutputStream());
        dos.writeBytes(postParams);
        dos.flush();
        dos.close();

        int statusCode = httpConn.getResponseCode();
        if (statusCode != 200) {
            System.out.println("请求出错！");
            return "";
        }
        InputStream ins = httpConn.getInputStream();

        byte[] readBuffer = new byte[1024];
        int len = 0;
        ByteArrayOutputStream output = new ByteArrayOutputStream();

        while ((len = ins.read(readBuffer)) > 0) {
            output.write(readBuffer, 0, len);
        }
        String httpReturn = output.toString("utf-8");
        output.close();
        ins.close();
        httpConn.disconnect();
        return httpReturn;
    }
}

HttpClient

虽然原生的HttpURLConnection已经能够满足大多数业务场景，但随着时间的推移和技术的发展，其不可不免的出现了一些局限性，比如使用繁琐、性能和安全性有待提升等，所以一些三方包进行了优化和封装，比如Apache的HttpClient和OkHttp。

Maven依赖

    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.5.6</version>
    </dependency>

代码示例

public class HttpUtil {

    private static final CloseableHttpClient httpClient = HttpClients.createDefault();

    /**
     * Apache HttpClient Get请求。
     *
     * @param getUrl
     * @return
     * @throws Exception
     */
    public static String sendGet(String getUrl) throws Exception {

        HttpGet hg = new HttpGet(getUrl);
        hg.addHeader("token", "vLx8IAq9nybErhP7");
        CloseableHttpResponse response = httpClient.execute(hg);
        String httpReturn = EntityUtils.toString(response.getEntity());
        response.close();
        return httpReturn;
    }

    /**
     * Apache HttpClient Post请求。
     *
     * @param postUrl
     * @param postParams
     * @return
     * @throws Exception
     */
    public static String sendPost(String postUrl, String postParams, String contentType) throws Exception {
        HttpPost hp = new HttpPost(postUrl);
        hp.setEntity(new StringEntity(postParams));
        hp.setHeader("Content-Type", contentType);

        hp.setConfig(RequestConfig.custom().setConnectTimeout(10).setSocketTimeout(3000).build()); //设置超时
        CloseableHttpResponse response = httpClient.execute(hp);
        String httpReturn = EntityUtils.toString(response.getEntity());
        response.close();
        return httpReturn;
    }
}

OkHttp

另外一个广受欢迎的Http三方包则是OkHttp。

maven依赖

    <dependency>
        <groupId>com.squareup.okhttp3</groupId>
        <artifactId>okhttp</artifactId>
        <version>3.8.1</version>
    </dependency>

代码示例

public class HttpUtil {

    private static final OkHttpClient httpClient = new OkHttpClient();

    /**
     * OkHttp Get请求。
     *
     * @param getUrl
     * @return
     * @throws Exception
     */
    public static String sendGet(String getUrl) throws Exception {
        Request request = new Request.Builder()
                .url(getUrl)
                .build();
        Response response = httpClient.newCall(request).execute();
        String httpReturn = "";
        if (response.isSuccessful())
            httpReturn = response.body().string();
        response.close();
        return httpReturn;
    }

    /**
     * OkHttp Post请求。
     *
     * @param postUrl
     * @param postParams
     * @return
     * @throws Exception
     */
    public static String sendPost(String postUrl, String postParams, String contentType) throws Exception {

        RequestBody postBody = RequestBody.create(MediaType.parse(contentType), postParams);

        Request request = new Request.Builder()
                .url(postUrl)
                .post(postBody)
                .build();
        Response response = httpClient.newCall(request).execute();
        String httpReturn = "";
        if (response.isSuccessful())
            httpReturn = response.body().string();
        response.close();
        return httpReturn;
    }
}