目前JAVA实现HTTP请求的方法用的最多的有两种：
一种是通过HTTPClient这种第三方的开源框架去实现。HTTPClient对HTTP的封装性比较不错，通过它基本上能够满足我们大部分的需求，HttpClient3.1 是 org.apache.commons.httpclient下操作远程 url的工具包，虽然已不再更新，但实现工作中使用httpClient3.1的代码还是很多，HttpClient4.5是org.apache.http.client下操作远程 url的工具包，最新的；
另一种则是通过HttpURLConnection去实现，HttpURLConnection是JAVA的标准类，是JAVA比较原生的一种实现方式。
第一种方式：java原生HttpURLConnection
package com.powerX.httpClient; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.OutputStream; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; public class HttpClient { public static String doGet(String httpurl) { HttpURLConnection connection = null; InputStream is = null; BufferedReader br = null; String result = null;// 返回结果字符串 try { // 创建远程url连接对象 URL url = new URL(httpurl); // 通过远程url连接对象打开一个连接，强转成httpURLConnection类 connection = (HttpURLConnection) url.openConnection(); // 设置连接方式：get connection.setRequestMethod("GET"); // 设置连接主机服务器的超时时间：15000毫秒 connection.setConnectTimeout(15000); // 设置读取远程返回的数据时间：60000毫秒 connection.setReadTimeout(60000); // 发送请求 connection.connect(); // 通过connection连接，获取输入流 if (connection.getResponseCode() == 200) { is = connection.getInputStream(); // 封装输入流is，并指定字符集 br = new BufferedReader(new InputStreamReader(is, "UTF-8")); // 存放数据 StringBuffer sbf = new StringBuffer(); String temp = null; while ((temp = br.readLine()) != null) { sbf.append(temp); sbf.append(" "); } result = sbf.toString(); } } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { // 关闭资源 if (null != br) { try { br.close(); } catch (IOException e) { e.printStackTrace(); } } if (null != is) { try { is.close(); } catch (IOException e) { e.printStackTrace(); } } connection.disconnect();// 关闭远程连接 } return result; } public static String doPost(String httpUrl, String param) { HttpURLConnection connection = null; InputStream is = null; OutputStream os = null; BufferedReader br = null; String result = null; try { URL url = new URL(httpUrl); // 通过远程url连接对象打开连接 connection = (HttpURLConnection) url.openConnection(); // 设置连接请求方式 connection.setRequestMethod("POST"); // 设置连接主机服务器超时时间：15000毫秒 connection.setConnectTimeout(15000); // 设置读取主机服务器返回数据超时时间：60000毫秒 connection.setReadTimeout(60000); // 默认值为：false，当向远程服务器传送数据/写数据时，需要设置为true connection.setDoOutput(true); // 默认值为：true，当前向远程服务读取数据时，设置为true，该参数可有可无 connection.setDoInput(true); // 设置传入参数的格式:请求参数应该是 name1=value1&name2=value2 的形式。 connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // 设置鉴权信息：Authorization: Bearer da3efcbf-0845-4fe3-8aba-ee040be542c0 connection.setRequestProperty("Authorization", "Bearer da3efcbf-0845-4fe3-8aba-ee040be542c0"); // 通过连接对象获取一个输出流 os = connection.getOutputStream(); // 通过输出流对象将参数写出去/传输出去,它是通过字节数组写出的 os.write(param.getBytes()); // 通过连接对象获取一个输入流，向远程读取 if (connection.getResponseCode() == 200) { is = connection.getInputStream(); // 对输入流对象进行包装:charset根据工作项目组的要求来设置 br = new BufferedReader(new InputStreamReader(is, "UTF-8")); StringBuffer sbf = new StringBuffer(); String temp = null; // 循环遍历一行一行读取数据 while ((temp = br.readLine()) != null) { sbf.append(temp); sbf.append(" "); } result = sbf.toString(); } } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { // 关闭资源 if (null != br) { try { br.close(); } catch (IOException e) { e.printStackTrace(); } } if (null != os) { try { os.close(); } catch (IOException e) { e.printStackTrace(); } } if (null != is) { try { is.close(); } catch (IOException e) { e.printStackTrace(); } } // 断开与远程地址url的连接 connection.disconnect(); } return result; } }
第二种方式：apache HttpClient3.1（已不再更新）
package com.powerX.httpClient; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.UnsupportedEncodingException; import java.util.Iterator; import java.util.Map; import java.util.Map.Entry; import java.util.Set; import org.apache.commons.httpclient.DefaultHttpMethodRetryHandler; import org.apache.commons.httpclient.HttpClient; import org.apache.commons.httpclient.HttpStatus; import org.apache.commons.httpclient.NameValuePair; import org.apache.commons.httpclient.methods.GetMethod; import org.apache.commons.httpclient.methods.PostMethod; import org.apache.commons.httpclient.params.HttpMethodParams; public class HttpClient3 { public static String doGet(String url) { // 输入流 InputStream is = null; BufferedReader br = null; String result = null; // 创建httpClient实例 HttpClient httpClient = new HttpClient(); // 设置http连接主机服务超时时间：15000毫秒 // 先获取连接管理器对象，再获取参数对象,再进行参数的赋值 httpClient.getHttpConnectionManager().getParams().setConnectionTimeout(15000); // 创建一个Get方法实例对象 GetMethod getMethod = new GetMethod(url); // 设置get请求超时为60000毫秒 getMethod.getParams().setParameter(HttpMethodParams.SO_TIMEOUT, 60000); // 设置请求重试机制，默认重试次数：3次，参数设置为true，重试机制可用，false相反 getMethod.getParams().setParameter(HttpMethodParams.RETRY_HANDLER, new DefaultHttpMethodRetryHandler(3, true)); try { // 执行Get方法 int statusCode = httpClient.executeMethod(getMethod); // 判断返回码 if (statusCode != HttpStatus.SC_OK) { // 如果状态码返回的不是ok,说明失败了,打印错误信息 System.err.println("Method faild: " + getMethod.getStatusLine()); } else { // 通过getMethod实例，获取远程的一个输入流 is = getMethod.getResponseBodyAsStream(); // 包装输入流 br = new BufferedReader(new InputStreamReader(is, "UTF-8")); StringBuffer sbf = new StringBuffer(); // 读取封装的输入流 String temp = null; while ((temp = br.readLine()) != null) { sbf.append(temp).append(" "); } result = sbf.toString(); } } catch (IOException e) { e.printStackTrace(); } finally { // 关闭资源 if (null != br) { try { br.close(); } catch (IOException e) { e.printStackTrace(); } } if (null != is) { try { is.close(); } catch (IOException e) { e.printStackTrace(); } } // 释放连接 getMethod.releaseConnection(); } return result; } public static String doPost(String url, Map<String, Object> paramMap) { // 获取输入流 InputStream is = null; BufferedReader br = null; String result = null; // 创建httpClient实例对象 HttpClient httpClient = new HttpClient(); // 设置httpClient连接主机服务器超时时间：15000毫秒 httpClient.getHttpConnectionManager().getParams().setConnectionTimeout(15000); // 创建post请求方法实例对象 PostMethod postMethod = new PostMethod(url); // 设置post请求超时时间 postMethod.getParams().setParameter(HttpMethodParams.SO_TIMEOUT, 60000); NameValuePair[] nvp = null; // 判断参数map集合paramMap是否为空 if (null != paramMap && paramMap.size() > 0) {// 不为空 // 创建键值参数对象数组，大小为参数的个数 nvp = new NameValuePair[paramMap.size()]; // 循环遍历参数集合map Set<Entry<String, Object>> entrySet = paramMap.entrySet(); // 获取迭代器 Iterator<Entry<String, Object>> iterator = entrySet.iterator(); int index = 0; while (iterator.hasNext()) { Entry<String, Object> mapEntry = iterator.next(); // 从mapEntry中获取key和value创建键值对象存放到数组中 try { nvp[index] = new NameValuePair(mapEntry.getKey(), new String(mapEntry.getValue().toString().getBytes("UTF-8"), "UTF-8")); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } index++; } } // 判断nvp数组是否为空 if (null != nvp && nvp.length > 0) { // 将参数存放到requestBody对象中 postMethod.setRequestBody(nvp); } // 执行POST方法 try { int statusCode = httpClient.executeMethod(postMethod); // 判断是否成功 if (statusCode != HttpStatus.SC_OK) { System.err.println("Method faild: " + postMethod.getStatusLine()); } // 获取远程返回的数据 is = postMethod.getResponseBodyAsStream(); // 封装输入流 br = new BufferedReader(new InputStreamReader(is, "UTF-8")); StringBuffer sbf = new StringBuffer(); String temp = null; while ((temp = br.readLine()) != null) { sbf.append(temp).append(" "); } result = sbf.toString(); } catch (IOException e) { e.printStackTrace(); } finally { // 关闭资源 if (null != br) { try { br.close(); } catch (IOException e) { e.printStackTrace(); } } if (null != is) { try { is.close(); } catch (IOException e) { e.printStackTrace(); } } // 释放连接 postMethod.releaseConnection(); } return result; } }
第三种方式：apache httpClient4.5
package com.powerX.httpClient; import java.io.IOException; import java.io.UnsupportedEncodingException; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Map.Entry; import java.util.Set; import org.apache.http.HttpEntity; import org.apache.http.NameValuePair; import org.apache.http.client.ClientProtocolException; import org.apache.http.client.config.RequestConfig; import org.apache.http.client.entity.UrlEncodedFormEntity; import org.apache.http.client.methods.CloseableHttpResponse; import org.apache.http.client.methods.HttpGet; import org.apache.http.client.methods.HttpPost; import org.apache.http.impl.client.CloseableHttpClient; import org.apache.http.impl.client.HttpClients; import org.apache.http.message.BasicNameValuePair; import org.apache.http.util.EntityUtils; public class HttpClient4 { public static String doGet(String url) { CloseableHttpClient httpClient = null; CloseableHttpResponse response = null; String result = ""; try { // 通过默认配置创建一个httpClient实例 httpClient = HttpClients.createDefault(); // 创建httpGet远程连接实例 HttpGet httpGet = new HttpGet(url); // 设置请求头信息，鉴权 httpGet.setHeader("Authorization", "Bearer da3efcbf-0845-4fe3-8aba-ee040be542c0"); // 设置配置请求参数 RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(35000)// 连接主机服务超时时间 .setConnectionRequestTimeout(35000)// 请求超时时间 .setSocketTimeout(60000)// 数据读取超时时间 .build(); // 为httpGet实例设置配置 httpGet.setConfig(requestConfig); // 执行get请求得到返回对象 response = httpClient.execute(httpGet); // 通过返回对象获取返回数据 HttpEntity entity = response.getEntity(); // 通过EntityUtils中的toString方法将结果转换为字符串 result = EntityUtils.toString(entity); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { // 关闭资源 if (null != response) { try { response.close(); } catch (IOException e) { e.printStackTrace(); } } if (null != httpClient) { try { httpClient.close(); } catch (IOException e) { e.printStackTrace(); } } } return result; } public static String doPost(String url, Map<String, Object> paramMap) { CloseableHttpClient httpClient = null; CloseableHttpResponse httpResponse = null; String result = ""; // 创建httpClient实例 httpClient = HttpClients.createDefault(); // 创建httpPost远程连接实例 HttpPost httpPost = new HttpPost(url); // 配置请求参数实例 RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(35000)// 设置连接主机服务超时时间 .setConnectionRequestTimeout(35000)// 设置连接请求超时时间 .setSocketTimeout(60000)// 设置读取数据连接超时时间 .build(); // 为httpPost实例设置配置 httpPost.setConfig(requestConfig); // 设置请求头 httpPost.addHeader("Content-Type", "application/x-www-form-urlencoded"); // 封装post请求参数 if (null != paramMap && paramMap.size() > 0) { List<NameValuePair> nvps = new ArrayList<NameValuePair>(); // 通过map集成entrySet方法获取entity Set<Entry<String, Object>> entrySet = paramMap.entrySet(); // 循环遍历，获取迭代器 Iterator<Entry<String, Object>> iterator = entrySet.iterator(); while (iterator.hasNext()) { Entry<String, Object> mapEntry = iterator.next(); nvps.add(new BasicNameValuePair(mapEntry.getKey(), mapEntry.getValue().toString())); } // 为httpPost设置封装好的请求参数 try { httpPost.setEntity(new UrlEncodedFormEntity(nvps, "UTF-8")); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } } try { // httpClient对象执行post请求,并返回响应参数对象 httpResponse = httpClient.execute(httpPost); // 从响应对象中获取响应内容 HttpEntity entity = httpResponse.getEntity(); result = EntityUtils.toString(entity); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { // 关闭资源 if (null != httpResponse) { try { httpResponse.close(); } catch (IOException e) { e.printStackTrace(); } } if (null != httpClient) { try { httpClient.close(); } catch (IOException e) { e.printStackTrace(); } } } return result; } }
有时候我们在使用post请求时，可能传入的参数是json或者其他格式，此时我们则需要更改请求头及参数的设置信息，
以httpClient4.5为例，更改下面两列配置：httpPost.setEntity(new StringEntity("你的json串")); httpPost.addHeader("Content-Type", "application/json")。