java发http请求

下面介绍两种方式 
1.使用jdk提供的URLConnection 
2.使用apache提供的HttpClient（封装了jdk）

一、使用URLConnect进行http请求

public class HttpUtil {

    /**
     * 向指定URL发送GET方法的请求
     *
     * @param url
     *            发送请求的URL
     * @param param
     *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
     * @return URL 所代表远程资源的响应结果
     */
    public static String sendGet(String url, String param) {
        String result = "";
        BufferedReader in = null;
        try {
            String urlNameString = url + "?" + param;
            URL realUrl = new URL(urlNameString);
            // 打开和URL之间的连接
            URLConnection connection = realUrl.openConnection();
            // 设置通用的请求属性
            connection.setRequestProperty("accept", "*/*");
            connection.setRequestProperty("connection", "Keep-Alive");
            connection.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 建立实际的连接
            connection.connect();
            // 获取所有响应头字段
            Map<String, List<String>> map = connection.getHeaderFields();
            // 遍历所有的响应头字段
            for (String key : map.keySet()) {
                System.out.println(key + "--->" + map.get(key));
            }
            // 定义 BufferedReader输入流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            System.out.println("发送GET请求出现异常！" + e);
            e.printStackTrace();
        }
        // 使用finally块来关闭输入流
        finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (Exception e2) {
                e2.printStackTrace();
            }
        }
        return result;
    }

    /**
     * 向指定 URL 发送POST方法的请求
     *
     * @param url
     *            发送请求的 URL
     * @param param
     *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
     * @return 所代表远程资源的响应结果
     */
    public static String sendPost(String url, String param) {
        PrintWriter out = null;
        BufferedReader in = null;
        String result = "";
        try {
            URL realUrl = new URL(url);
            // 打开和URL之间的连接
            URLConnection conn = realUrl.openConnection();
            // 设置通用的请求属性
            conn.setRequestProperty("accept", "*/*");
            conn.setRequestProperty("connection", "Keep-Alive");
            conn.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 发送POST请求必须设置如下两行
            conn.setDoOutput(true);
            conn.setDoInput(true);
            // 获取URLConnection对象对应的输出流
            out = new PrintWriter(conn.getOutputStream());
            // 发送请求参数
            out.print(param);
            // flush输出流的缓冲
            out.flush();
            // 定义BufferedReader输入流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            System.out.println("发送 POST 请求出现异常！" + e);
            e.printStackTrace();
        }
        // 使用finally块来关闭输出流、输入流
        finally {
            try {
                if (out != null) {
                    out.close();
                }
                if (in != null) {
                    in.close();
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
        return result;
    }

    public static void main(String[] args) {
        // 发送 GET 请求
        String result = HttpUtil.sendGet("http://baidu.com", "key=123&v=456");
        System.out.println("result: " + result);
        System.out.println("-----------------------------------------------------");
        // 发送 POST 请求
        String sr = HttpUtil.sendPost("http://baidu.com", "key=123&v=456");
        System.out.println("sr: " + sr);
    }
}

二、使用HttpClient进行http请求

maven依赖：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.3</version>
</dependency>

代码：

public class HttpClientUtil {
    public static void get() {
        /**
         * client和response需要关闭资源
         */
        // 创建client,放入try()中自动释放,不需要finally
        try (CloseableHttpClient client = HttpClientBuilder.create().build()) {

            // 执行得到response
            try (CloseableHttpResponse response = client.execute(new HttpGet("http://www.baidu.com"))) {
                // 获取statusCode
                Integer statusCode = response.getStatusLine().getStatusCode();
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    // body
                    String bodyAsString = EntityUtils.toString(entity);
                    // Media Type
                    String contentMimeType = ContentType.getOrDefault(entity).getMimeType();
                    // head
                    Header[] headers = response.getHeaders(HttpHeaders.CONTENT_TYPE);
                    // 输出
                    System.out.println("statusCode:" + statusCode);
                    System.out.println("contentMinmeType:" + contentMimeType);
                    System.out.println("body:" + bodyAsString);
                    System.out.println("head" + headers);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void post() {
        // 创建client
        try (CloseableHttpClient client = HttpClientBuilder.create().build()) {
            HttpPost postRequest = new HttpPost("http://www.baidu.com");
            // 添加请求参数
            List<NameValuePair> params = new ArrayList<>();
            params.add(new BasicNameValuePair("key1", "value1"));
            params.add(new BasicNameValuePair("key2", "value2"));
            postRequest.setEntity(new UrlEncodedFormEntity(params, Consts.UTF_8));
            // 执行并获取返回结果到response
            try (CloseableHttpResponse response = client.execute(postRequest)) {
                // 获取statusCode
                Integer statusCode = response.getStatusLine().getStatusCode();
                // Media Type
                String contentMimeType = ContentType.getOrDefault(response.getEntity()).getMimeType();
                // body
                String bodyAsString = EntityUtils.toString(response.getEntity());
                // head
                Header[] headers = response.getHeaders(HttpHeaders.CONTENT_TYPE);
                System.out.println("statusCode:" + statusCode);
                System.out.println("contentMinmeType:" + contentMimeType);
                System.out.println("body:" + bodyAsString);
                System.out.println("head" + headers);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        get();
        System.out.println("------------------------------------");
        post();
    }
}

转载：

https://blog.csdn.net/ludonglue/article/details/78038643