HttpURLConnection是JDK自身提供的网络类，不需要引入额外的jar包。文中所使用到的软件版本：Java 1.8.0_191。

1、服务端

参见Java调用Http接口(1)--编写服务端

2、调用Http接口

2.1、GET请求

    public static void get() {

        try {

            String requestPath = "http://localhost:8080/demo/httptest/getUser?userId=1000&userName=" + URLEncoder.encode("李白", "utf-8");

            URL url = new URL(requestPath);

            //设置代理

            //InetSocketAddress addr = new InetSocketAddress("127.0.0.1", 8888);

            //Proxy proxy = new Proxy(Proxy.Type.HTTP, addr);

            //connection = (HttpURLConnection)url.openConnection(proxy);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("GET");

            connection.connect();

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("GET返回结果：" + back);

            } else {

                System.out.println("GET请求状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

2.2、POST请求(发送键值对数据）

    public static void post() {

        try {

            String requestPath = "http://localhost:8080/demo/httptest/getUser";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.setDoOutput(true);

            connection.connect();

            String param = "userId=1000&userName=李白";

            bytesToOutputStream(param.getBytes(), connection.getOutputStream());

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("POST返回结果：" + back);

            } else {

                System.out.println("POST返回状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

2.3、POST请求(发送JSON数据）

    public static void post2() {

        try {

            String requestPath = "http://localhost:8080/demo/httptest/addUser";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.setDoOutput(true);

            connection.setRequestProperty("Content-type", "application/json");

            connection.connect();

            String param = "{\"userId\": \"1001\",\"userName\":\"杜甫\"}";

            bytesToOutputStream(param.getBytes(), connection.getOutputStream());

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("POST2返回结果：" + back);

            } else {

                System.out.println("POST2返回状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

2.4、上传文件

    public static void upload() {

        try {

            String requestPath = "http://localhost:8080/demo/httptest/upload";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.setDoOutput(true);

            connection.setRequestProperty("Content-type", "file/*");

            connection.connect();

            FileInputStream fileInputStream = new FileInputStream("d:/a.jpg");

            inputStreamToOutputStream(fileInputStream, connection.getOutputStream());

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("upload返回结果：" + back);

            } else {

                System.out.println("upload返回状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

2.5、上传文件及发送键值对数据

2.5.1、分析数据结构

通过抓包工具分析页面表单上传文件的过程，可以看出传输数据的结构：

2.5.2、根据分析出的数据结构编写代码

    public static void multi() {

        String BOUNDARY = java.util.UUID.randomUUID().toString();

        String TWO_HYPHENS = "--";

        String LINE_END = "\r\n";

        FileInputStream in = null;

        try {

            String requestPath = "http://localhost:8080/demo/httptest/multi";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.setDoOutput(true);

            connection.setDoInput(true);

            connection.setRequestProperty("Content-type", "multipart/form-data; BOUNDARY=" + BOUNDARY);

            connection.connect();

            StringBuffer sb = new StringBuffer();

            //封装键值对数据1

            sb.append(TWO_HYPHENS).append(BOUNDARY).append(LINE_END);

            sb.append("Content-Disposition: form-data; name=\"param1\"").append(LINE_END);

            sb.append(LINE_END);

            sb.append("参数1").append(LINE_END);

            //封装键值对数据2

            sb.append(TWO_HYPHENS).append(BOUNDARY).append(LINE_END);

            sb.append("Content-Disposition: form-data; name=\"param2\"").append(LINE_END);

            sb.append(LINE_END);

            sb.append("参数2").append(LINE_END);

            //封装文件数据

            sb.append(TWO_HYPHENS).append(BOUNDARY).append(LINE_END);

            sb.append("Content-Disposition: form-data; name=\"file\"; filename=\"a.jpg\"").append(LINE_END);

            sb.append("Content-Type: file/*").append(LINE_END);

            sb.append(LINE_END);

            bytesToOutputStream(sb.toString().getBytes(), connection.getOutputStream());

            in = new FileInputStream("d:/a.jpg");

            inputStreamToOutputStream(in, connection.getOutputStream());

            //写入标记结束位

            String end = (LINE_END + TWO_HYPHENS + BOUNDARY + TWO_HYPHENS + LINE_END);

            bytesToOutputStream(end.getBytes(), connection.getOutputStream());

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("multi返回结果：" + back);

            } else {

                System.out.println("multi返回状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            FileUtil.close(in);

        }

    }

2.5.3、上传文件方法变通

这种方式上传文件完全是模拟页面的提交行为来编码的，比较繁琐。可以把文件转成字符串，然后通过键值对传给服务端，服务端执行相反的过程来存储文件：

客户端：文件-> 字节数组->Base64字符串

服务端：Base64字符串-> 字节数组->文件

按照这种方式来实现应该比较容易，这里就不演示了。

2.6、下载文件

    public static void download() {

        FileOutputStream out = null;

        try {

            String requestPath = "http://localhost:8080/demo/httptest/download";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.connect();

            System.out.println("download返回状态码：" + connection.getResponseCode());

            String contentDisposition = connection.getHeaderField("Content-Disposition");//attachment; filename="a.jpg"

            String fileName = "none";

            if (contentDisposition != null && contentDisposition.indexOf("filename") > -1) {

                fileName = contentDisposition.substring(contentDisposition.indexOf("\"") + 1, contentDisposition.length() - 1);

                fileName = java.net.URLDecoder.decode(fileName, "utf-8");

            }

            out = new FileOutputStream("d:/temp/dowload_" + System.currentTimeMillis() + "_" + fileName);

            inputStreamToOutputStream(connection.getInputStream(), out);

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            FileUtil.close(out);

        }

    }

2.7、完整例子

package com.inspur.demo.http.client;

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.net.HttpURLConnection;

//import java.net.InetSocketAddress;

//import java.net.Proxy;

import java.net.URL;

import java.net.URLEncoder;

import com.inspur.demo.common.util.FileUtil;

/**

 *

 * 通过HttpURLConnection调用Http接口

 *

 */

public class HttpURLConnectionCase {

    /**

     * GET请求

     */

    public static void get() {

        try {

            String requestPath = "http://localhost:8080/demo/httptest/getUser?userId=1000&userName=" + URLEncoder.encode("李白", "utf-8");

            URL url = new URL(requestPath);

            //设置代理

            //InetSocketAddress addr = new InetSocketAddress("127.0.0.1", 8888);

            //Proxy proxy = new Proxy(Proxy.Type.HTTP, addr);

            //connection = (HttpURLConnection)url.openConnection(proxy);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("GET");

            connection.connect();

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("GET返回结果：" + back);

            } else {

                System.out.println("GET请求状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    /**

     * POST请求，发送键值对数据

     */

    public static void post() {

        try {

            String requestPath = "http://localhost:8080/demo/httptest/getUser";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.setDoOutput(true);

            connection.connect();

            String param = "userId=1000&userName=李白";

            bytesToOutputStream(param.getBytes(), connection.getOutputStream());

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("POST返回结果：" + back);

            } else {

                System.out.println("POST返回状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    /**

     * POST请求，发送json格式数据

     */

    public static void post2() {

        try {

            String requestPath = "http://localhost:8080/demo/httptest/addUser";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.setDoOutput(true);

            connection.setRequestProperty("Content-type", "application/json");

            connection.connect();

            String param = "{\"userId\": \"1001\",\"userName\":\"杜甫\"}";

            bytesToOutputStream(param.getBytes(), connection.getOutputStream());

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("POST2返回结果：" + back);

            } else {

                System.out.println("POST2返回状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    /**

     * 上传文件

     */

    public static void upload() {

        try {

            String requestPath = "http://localhost:8080/demo/httptest/upload";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.setDoOutput(true);

            connection.setRequestProperty("Content-type", "file/*");

            connection.connect();

            FileInputStream fileInputStream = new FileInputStream("d:/a.jpg");

            inputStreamToOutputStream(fileInputStream, connection.getOutputStream());

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("upload返回结果：" + back);

            } else {

                System.out.println("upload返回状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    /**

     * 上传文件及发送键值对数据

     */

    public static void multi() {

        String BOUNDARY = java.util.UUID.randomUUID().toString();

        String TWO_HYPHENS = "--";

        String LINE_END = "\r\n";

        FileInputStream in = null;

        try {

            String requestPath = "http://localhost:8080/demo/httptest/multi";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.setDoOutput(true);

            connection.setDoInput(true);

            connection.setRequestProperty("Content-type", "multipart/form-data; BOUNDARY=" + BOUNDARY);

            connection.connect();

            StringBuffer sb = new StringBuffer();

            //封装键值对数据1

            sb.append(TWO_HYPHENS).append(BOUNDARY).append(LINE_END);

            sb.append("Content-Disposition: form-data; name=\"param1\"").append(LINE_END);

            sb.append(LINE_END);

            sb.append("参数1").append(LINE_END);

            //封装键值对数据2

            sb.append(TWO_HYPHENS).append(BOUNDARY).append(LINE_END);

            sb.append("Content-Disposition: form-data; name=\"param2\"").append(LINE_END);

            sb.append(LINE_END);

            sb.append("参数2").append(LINE_END);

            //封装文件数据

            sb.append(TWO_HYPHENS).append(BOUNDARY).append(LINE_END);

            sb.append("Content-Disposition: form-data; name=\"file\"; filename=\"a.jpg\"").append(LINE_END);

            sb.append("Content-Type: file/*").append(LINE_END);

            sb.append(LINE_END);

            bytesToOutputStream(sb.toString().getBytes(), connection.getOutputStream());

            in = new FileInputStream("d:/a.jpg");

            inputStreamToOutputStream(in, connection.getOutputStream());

            //写入标记结束位

            String end = (LINE_END + TWO_HYPHENS + BOUNDARY + TWO_HYPHENS + LINE_END);

            bytesToOutputStream(end.getBytes(), connection.getOutputStream());

            if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {

                byte[] b = getBytesFromInputStream(connection.getInputStream());

                String back = new String(b);

                System.out.println("multi返回结果：" + back);

            } else {

                System.out.println("multi返回状态码：" + connection.getResponseCode());

            }

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            FileUtil.close(in);

        }

    }

    /**

     * 下载文件

     */

    public static void download() {

        FileOutputStream out = null;

        try {

            String requestPath = "http://localhost:8080/demo/httptest/download";

            URL url = new URL(requestPath);

            HttpURLConnection connection = (HttpURLConnection)url.openConnection();

            connection.setRequestMethod("POST");

            connection.connect();

            System.out.println("download返回状态码：" + connection.getResponseCode());

            String contentDisposition = connection.getHeaderField("Content-Disposition");//attachment; filename="a.jpg"

            String fileName = "none";

            if (contentDisposition != null && contentDisposition.indexOf("filename") > -1) {

                fileName = contentDisposition.substring(contentDisposition.indexOf("\"") + 1, contentDisposition.length() - 1);

                fileName = java.net.URLDecoder.decode(fileName, "utf-8");

            }

            out = new FileOutputStream("d:/temp/dowload_" + System.currentTimeMillis() + "_" + fileName);

            inputStreamToOutputStream(connection.getInputStream(), out);

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            FileUtil.close(out);

        }

    }

    /**

     * 从输入流获取数据

     * @param in

     * @return

     * @throws IOException

     */

    private static byte[] getBytesFromInputStream(InputStream in) throws IOException {

        ByteArrayOutputStream out = new ByteArrayOutputStream();

        byte[] b = new byte[1024];

        int len;

        while ((len = in.read(b)) != -1) {

            out.write(b, 0, len);

        }

        byte[] bytes = out.toByteArray();

        out.close();

        return bytes;

    }

    /**

     * 把字节数组写入输出流

     * @param bytes

     * @param out

     * @throws IOException

     */

    private static void bytesToOutputStream(byte[] bytes, OutputStream out) throws IOException {

        ByteArrayInputStream in = new ByteArrayInputStream(bytes);

        byte[] b = new byte[1024];

        int len;

        while ((len = in.read(b)) != -1) {

            out.write(b, 0, len);

        }

        out.flush();

        in.close();

    }

    /**

     * 从输入流读取数据并写入输出流

     * @param out

     * @param bytes

     * @throws IOException

     */

    private static void inputStreamToOutputStream(InputStream in, OutputStream out) throws IOException {

        byte[] b = new byte[1024];

        int len;

        while ((len = in.read(b)) != -1) {

            out.write(b, 0, len);

        }

        out.flush();

    }

    public static void main(String[] args) {

        get();

        post();

        post2();

        upload();

        multi();

        download();

    }

}

3、调用Https接口

调用Https接口需要用HttpsURLConnection，与调用Http接口不一样的部分主要在设置ssl部分，下面用GET请求来演示ssl的设置，其他调用方式类似。

3.1、导入cer证书

对于自定义证书的网站，需把证书用java自带的工具keytool导入本地，如导入到d:/temp目录下

cd d:/temp
keytool -import -alias aa -keystore cacerts -file aa.cer -trustcacerts

如果当前目录已有cacerts证书库，则需输入密码；如果没有则需设置密码，会在当前目录下生成cacerts证书库。

也可以不导入，使用默认实现的DefaultTrustManager，信任所有，将导致不安全。

3.2、示例

package com.inspur.demo.http.client;

import java.io.ByteArrayOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.net.URL;

import java.security.KeyStore;

import java.security.cert.CertificateException;

import java.security.cert.X509Certificate;

import javax.net.ssl.HostnameVerifier;

import javax.net.ssl.HttpsURLConnection;

import javax.net.ssl.KeyManager;

import javax.net.ssl.KeyManagerFactory;

import javax.net.ssl.SSLContext;

import javax.net.ssl.SSLSession;

import javax.net.ssl.SSLSocketFactory;

import javax.net.ssl.TrustManager;

import javax.net.ssl.TrustManagerFactory;

import javax.net.ssl.X509TrustManager;

import com.inspur.demo.common.util.FileUtil;

/**

 * 通过HttpsURLConnection调用Https接口

 */

public class HttpsURLConnectionCase {

    public static void main(String[] args) {

        try {

            /*

             * 请求有权威证书的地址

             */

            String requestPath = "https://www.baidu.com/";

            HttpsURLConnection connection = getHttpsURLConnection(requestPath, "GET");

            String result = new String(getBytesFromInputStream(connection.getInputStream()));

            System.out.println("GET1返回结果：" + result);

            /*

             * 请求自定义证书的地址

             */

            //获取信任库

            KeyStore trustStore = getkeyStore("jks", "d:/temp/cacerts", "123456");

            //不需客户端证书

            requestPath = "https://x.x.x.x:9010/zsywservice";

            connection = getHttpsURLConnection(requestPath, "GET", null, null, trustStore);

            result = new String(getBytesFromInputStream(connection.getInputStream()));

            System.out.println("GET2返回结果：" + result);

            //需客户端证书

            requestPath = "https://x.x.x.x:9016/zsywservice";

            KeyStore keyStore = getkeyStore("pkcs12", "d:/client.p12", "123456");

            connection = getHttpsURLConnection(requestPath, "GET", keyStore, "123456", trustStore);

            result = new String(getBytesFromInputStream(connection.getInputStream()));

            System.out.println("GET3返回结果：" + result);

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    /**

     * 获取证书

     * @return

     */

    private static KeyStore getkeyStore(String type, String filePath, String password) {

        KeyStore keySotre = null;

        FileInputStream in = null;

        try {

            keySotre = KeyStore.getInstance(type);

            in = new FileInputStream(new File(filePath));

            keySotre.load(in, password.toCharArray());

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            FileUtil.close(in);

        }

        return keySotre;

    }

    private static HttpsURLConnection getHttpsURLConnection(String uri, String method) throws Exception {

        URL url = new URL(uri);

        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();

        connection.setRequestMethod(method);

        connection.setDoInput(true);

        connection.setDoOutput(true);

        return connection;

    }

    /**

     * 获取连接

     * @param uri

     * @param method

     * @param keyStore

     * @param trustStore

     * @return

     * @throws Exception

     */

    private static HttpsURLConnection getHttpsURLConnection(String uri, String method, KeyStore keyStore, String keyStorePassword, KeyStore trustStore) throws Exception {

        KeyManager[] keyManagers = null;

        TrustManager[] trustManagers = null;

        if (keyStore != null) {

            KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance("SunX509");

            keyManagerFactory.init(keyStore, keyStorePassword.toCharArray());

            keyManagers = keyManagerFactory.getKeyManagers();

        }

        if (trustStore != null) {

            TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance("SunX509");

            trustManagerFactory.init(trustStore);

            trustManagers = trustManagerFactory.getTrustManagers();

        } else {

            trustManagers = new TrustManager[] { new DefaultTrustManager()};

        }

        //设置服务端支持的协议

        SSLContext context = SSLContext.getInstance("TLSv1.2");

        context.init(keyManagers, trustManagers, null);

        SSLSocketFactory sslFactory = context.getSocketFactory();

        URL url = new URL(uri);

        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();

        connection.setSSLSocketFactory(sslFactory);

        //验证URL的主机名和服务器的标识主机名是否匹配

        connection.setHostnameVerifier(new HostnameVerifier() {

            @Override

            public boolean verify(String hostname, SSLSession session) {

                //if ("xxx".equals(hostname)) {

                //    return true;

                //} else {

                //    return false;

                //}

                return true;

            }

        });

        connection.setRequestMethod(method);

        connection.setDoInput(true);

        connection.setDoOutput(true);

        return connection;

    }

    /**

     * 默认的TrustManager实现，不安全

     */

    private static final class DefaultTrustManager implements X509TrustManager {

        @Override

        public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {

        }

        @Override

        public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {

        }

        @Override

        public X509Certificate[] getAcceptedIssuers() {

            return null;

        }

    }

    /**

     * 从输入流获取数据

     * @param in

     * @return

     * @throws IOException

     */

    private static byte[] getBytesFromInputStream(InputStream in) throws IOException {

        ByteArrayOutputStream out = new ByteArrayOutputStream();

        byte[] b = new byte[1024];

        int len;

        while ((len = in.read(b)) != -1) {

            out.write(b, 0, len);

        }

        byte[] bytes = out.toByteArray();

        out.close();

        return bytes;

    }

}

3.2、Received fatal alert:handshake_failure

出现这种这种问题的一种情况是由于客户端使用的协议，服务端不支持造成的；修改为服务端所支持的协议即可。在getHttpsURLConnection方法中修改：

SSLContext context = SSLContext.getInstance("TLSv1.2");

可选的协议参数有：SSL、SSLv2、SSLv3、TLS、TLSv1、TLSv1.1、TLSv1.2；TLS是SSL标准化的产物，故现在基本只使用TLS相关的参数。

可以用linux的curl命令来测试服务端支持哪些协议：

curl -k https://x.x.x.x:9016/zsywservice --tlsv1.2 -v

可选协议有：--tlsv1、--tlsv1.0、--tlsv1.1、--tlsv1.2、--tlsv1.3

如果出现如下信息，则表示不支持：

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