介紹HttpClient庫的使用前，先介紹jdk裡HttpURLConnection，因為HttpClient是開源的第三方庫，使用方便，不過jdk裡的都是比較基本的，有時候沒有HttpClient的時候也可以使用jdk裡的HttpURLConnection，HttpURLConnection都是調jdk java.net庫的，下面給出例項程式碼：
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"); // 設定請求方式
conn.setRequestProperty("Content-Type", "application/json"); // 設定傳送資料的
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("傳送 POST 請求出現異常！" + 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);
}
}
然後介紹一下HttpClient，只給出例項程式碼，不封裝成工具類，因為理解基本用法後，自己封裝工具類也是很容易的
HttpClient的GET請求
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請求，與GET請求類似
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();上面例子是可以支援訪問簽名要求沒那麼高的介面，然後訪問自簽名https的站點，那就要建立一個自定義的SSLContext物件，該物件要有可以儲存信任金鑰的容器，還要有判斷當前連線是否受信任的策略，以及在SSL連線工廠中取消對所有主機名的驗證，如果還是使用預設的HttpClient是會有下面的異常：
PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
給出解決方法：
public static CloseableHttpClient getClient() {
RegistryBuilder<ConnectionSocketFactory> registryBuilder = RegistryBuilder.create();
ConnectionSocketFactory plainSF = new PlainConnectionSocketFactory();
registryBuilder.register("http", plainSF);
// 指定信任金鑰儲存物件和連線套接字工廠
try {
KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
// 信任任何連結
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();
// 設定連線管理器
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();
}然後CloseableHttpClient httpClient = getClient()就可以
然後HttpClient語法相對比較繁雜？如果覺得比較麻煩，可以用Spring框架的RestTemplate，這裡要建立一個自定義的bean，根據需要建立，程式碼示例：
//訪問自簽名https的要點
HttpComponentsClientHttpRequestFactory requestFactory =
new HttpComponentsClientHttpRequestFactory(HttpClientUtil.getClient());
RestTemplate restTemplate = new RestTemplate(requestFactory);*/
try {
//Bean result= restTemplate.getForObject(digitalgdOauthUrl, Bean.class);