Http系列之接口调用示例教程

浅浅的花香味﹌ 2021-09-30 06:36 302阅读 0赞

介绍HttpClient库的使用前，先介绍jdk里HttpURLConnection，因为HttpClient是开源的第三方库，使用方便，不过jdk里的都是比较基本的，有时候没有HttpClient的时候也可以使用jdk里的HttpURLConnection，HttpURLConnection都是调jdk java.net库的，下面给出实例代码：

import sun.misc.BASE64Encoder;
    import java.io.*;
    import java.net.HttpURLConnection;
    import java.net.URL;
    import java.net.URLConnection;
    
    public class Main {
        public static void main(String[] args) throws Exception {
            String url = "https://ocr-api.ccint.com/ocr_service?app_key=%s";
            String appKey = "xxxxxx"; // your app_key
          String appSecret = "xxxxxx"; // your app_secret
          url = String.format(url, appKey);
            OutputStreamWriter out = null;
            BufferedReader in = null;
            String result = "";
            try {
                String imgData = imageToBase64("example.jpg");
                String param="{\"app_secret\":\"%s\",\"image_data\":\"%s\"}";
                param=String.format(param,appSecret,imgData);
                URL realUrl = new URL(url);
                HttpURLConnection conn = (HttpURLConnection) realUrl.openConnection();
                conn.setRequestProperty("accept", "*/*");
                conn.setRequestProperty("connection", "Keep-Alive");
                conn.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
                conn.setDoOutput(true);
                conn.setDoInput(true);
                conn.setRequestMethod("POST"); // 设置请求方式
                conn.setRequestProperty("Content-Type", "application/json"); // 设置发送数据的
                conn.connect();
                out = new OutputStreamWriter(conn.getOutputStream(), "UTF-8");
                out.append(param);
                out.flush();
                out.close();
                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();
            }
            finally {
                try {
                    if (out != null) {
                        out.close();
                    }
                    if (in != null) {
                        in.close();
                    }
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
            System.out.println(result);
        }
        public static String imageToBase64(String path)
        {
            String imgFile = path;
            InputStream in = null;
            byte[] data = null;
            try
            {
                in = new FileInputStream(imgFile);
                data = new byte[in.available()];
                in.read(data);
                in.close();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
            BASE64Encoder encoder = new BASE64Encoder();
            return encoder.encode(data);
        }
    }

然后介绍一下HttpClient，只给出实例代码，不封装成工具类，因为理解基本用法后，自己封装工具类也是很容易的

HttpClient的GET请求

CloseableHttpClient httpClient = HttpClients.createDefault();
        //https://github.com/search?utf8=%E2%9C%93&q=jeeplatform&type=
        URIBuilder uriBuilder = new URIBuilder("https://github.com/search");
        uriBuilder.addParameter("q","jeeplatform");
        HttpGet httpGet = new HttpGet(uriBuilder.build());
        CloseableHttpResponse httpResponse = httpClient.execute(httpGet);
        int statusCode = httpResponse.getStatusLine().getStatusCode();
        if(statusCode==200){
            HttpEntity entity = httpResponse.getEntity();
            System.out.println(EntityUtils.toString(entity,"UTF-8"));
        }
        httpClient.close();
        httpResponse.close();

HttpClient的POST请求，与GET请求类似

CloseableHttpClient httpClient = HttpClients.createDefault();
        //https://www.sogou.com/sie?query=%E8%8A%B1%E5%8D%83%E9%AA%A8&hdq=AQ7CZ&ekv=3&ie=utf8&
        String uri = "https://www.sogou.com/sie";
        List<NameValuePair> params= new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("query","花千骨"));
        StringEntity entity = new UrlEncodedFormEntity(params,"UTF-8");
        HttpPost httpPost = new HttpPost(uri);
        httpPost.setEntity(entity);
        CloseableHttpResponse httpResponse = httpClient.execute(httpPost);
        int statusCode = httpResponse.getStatusLine().getStatusCode();
        if(statusCode == 200){
            System.out.println(EntityUtils.toString(httpResponse.getEntity()));
        }
        httpClient.close();
        httpResponse.close();

上面例子是可以支持访问签名要求没那么高的接口，然后访问自签名https的站点，那就要建立一个自定义的SSLContext对象，该对象要有可以存储信任密钥的容器，还要有判断当前连接是否受信任的策略，以及在SSL连接工厂中取消对所有主机名的验证，如果还是使用默认的HttpClient是会有下面的异常：

> PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

给出解决方法：

public static CloseableHttpClient getClient() {
    		RegistryBuilder<ConnectionSocketFactory> registryBuilder = RegistryBuilder.create();
    		ConnectionSocketFactory plainSF = new PlainConnectionSocketFactory();
    		registryBuilder.register("http", plainSF);
    		// 指定信任密钥存储对象和连接套接字工厂
    		try {
    			KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
    			// 信任任何链接
    			TrustStrategy anyTrustStrategy = new TrustStrategy() {
    				@Override
    				public boolean isTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
    					return true;
    				}
    			};
    			SSLContext sslContext = SSLContexts.custom().useTLS().loadTrustMaterial(trustStore, anyTrustStrategy).build();
    			LayeredConnectionSocketFactory sslSF = new SSLConnectionSocketFactory(sslContext, SSLConnectionSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER);
    			registryBuilder.register("https", sslSF);
    		} catch (KeyStoreException e) {
    			throw new RuntimeException(e);
    		} catch (KeyManagementException e) {
    			throw new RuntimeException(e);
    		} catch (NoSuchAlgorithmException e) {
    			throw new RuntimeException(e);
    		}
    		Registry<ConnectionSocketFactory> registry = registryBuilder.build();
    		// 设置连接管理器
    		PoolingHttpClientConnectionManager connManager = new PoolingHttpClientConnectionManager(registry);
    		RequestConfig requestConfig = RequestConfig.custom().setSocketTimeout(TIMEOUT_SECONDS * 1000).setConnectTimeout(TIMEOUT_SECONDS * 1000).build();
    		return HttpClientBuilder.create().setConnectionManager(connManager).setMaxConnTotal(POOL_SIZE).setMaxConnPerRoute(POOL_SIZE).setDefaultRequestConfig(requestConfig).build();
    	}

然后CloseableHttpClient httpClient = getClient()就可以

然后HttpClient语法相对比较繁杂？如果觉得比较麻烦，可以用Spring框架的RestTemplate，这里要创建一个自定义的bean，根据需要创建，代码示例：

//访问自签名https的要点
    HttpComponentsClientHttpRequestFactory requestFactory = 
    					new HttpComponentsClientHttpRequestFactory(HttpClientUtil.getClient());
    		 RestTemplate restTemplate = new RestTemplate(requestFactory);*/
    		 
    			Bean result= restTemplate.getForObject(digitalgdOauthUrl, Bean.class);