Http接口调用示例教程

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 = "http://img.558idc.com/uploadfile/allimg/java/String.format(url, appKey);br OutputStreamWriter out = null;br BufferedReader in = null;br String result = ;br try {br 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);