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

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>

public static void main(String[] args) {        get();        post();    }    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();        }    }

代码：https://github.com/ludonglue/httpRequest

参考内容：
URLConnection：http://blog.csdn.net/iijse/article/details/6201101
HttpClient：http://www.baeldung.com/httpclient-guide