Httpclient简介

什么是httpclient

HTTP 协议可能是现在 Internet 上使用得最多、最重要的协议了，越来越多的 Java 应用程序需要直接通过 HTTP 协议来访问网络资源。虽然在 JDK 的 java net包中已经提供了访问 HTTP 协议的基本功能，但是对于大部分应用程序来说，JDK 库本身提供的功能还不够丰富和灵活。HttpClient 是 Apache Jakarta Common 下的子项目，用来提供高效的、最新的、功能丰富的支持 HTTP 协议的客户端编程工具包，并且它支持 HTTP 协议最新的版本和建议。

下载地址：

http://hc.apache.org/

功能介绍

以下列出的是 HttpClient 提供的主要的功能，要知道更多详细的功能可以参见 HttpClient 的主页。
（1）实现了所有 HTTP 的方法（GET,POST,PUT,HEAD 等）
（2）支持自动转向
（3）支持 HTTPS 协议
（4）支持代理服务器等

导入依赖

执行GET请求

public class DoGET {

public static void main(String[] args) throws Exception {

// 创建Httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();

// 创建http GET请求
HttpGet httpGet = new HttpGet("http://www.baidu.com/");

CloseableHttpResponse response = null;
try {
// 执行请求
response = httpclient.execute(httpGet);
// 判断返回状态是否为200
if (response.getStatusLine().getStatusCode() == 200) {
String content = EntityUtils.toString(response.getEntity(), "UTF-8");
System.out.println("内容长度：" + content.length());
//                FileUtils.writeStringToFile(new File("C:\\baidu.html"), content);
}
} finally {
if (response != null) {
response.close();
}
httpclient.close();
}

}

}

执行GET带参数

public class DoGETParam {

public static void main(String[] args) throws Exception {

// 创建Httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();

// 定义请求的参数
URI uri = new URIBuilder("http://www.baidu.com/s").setParameter("wd", "java").build();

System.out.println(uri);

// 创建http GET请求
HttpGet httpGet = new HttpGet(uri);

CloseableHttpResponse response = null;
try {
// 执行请求
response = httpclient.execute(httpGet);
// 判断返回状态是否为200
if (response.getStatusLine().getStatusCode() == 200) {
String content = EntityUtils.toString(response.getEntity(), "UTF-8");
System.out.println(content);
}
} finally {
if (response != null) {
response.close();
}
httpclient.close();
}

}

}

执行post请求

public class DoPOST {

public static void main(String[] args) throws Exception {

// 创建Httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();

// 创建http POST请求
HttpPost httpPost = new HttpPost("http://www.oschina.net/");

CloseableHttpResponse response = null;
try {
// 执行请求
response = httpclient.execute(httpPost);
// 判断返回状态是否为200
if (response.getStatusLine().getStatusCode() == 200) {
String content = EntityUtils.toString(response.getEntity(), "UTF-8");
System.out.println(content);
}
} finally {
if (response != null) {
response.close();
}
httpclient.close();
}

}

}

带参数的post请求

public class DoPOSTParam {

public static void main(String[] args) throws Exception {

// 创建Httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();

// 创建http POST请求
HttpPost httpPost = new HttpPost("http://www.oschina.net/search");

// 设置2个post参数，一个是scope、一个是q
List<NameValuePair> parameters = new ArrayList<NameValuePair>(0);
parameters.add(new BasicNameValuePair("scope", "project"));
parameters.add(new BasicNameValuePair("q", "java"));
// 构造一个form表单式的实体
UrlEncodedFormEntity formEntity = new UrlEncodedFormEntity(parameters);
// 将请求实体设置到httpPost对象中
httpPost.setEntity(formEntity);

CloseableHttpResponse response = null;
try {
// 执行请求
response = httpclient.execute(httpPost);
// 判断返回状态是否为200
if (response.getStatusLine().getStatusCode() == 200) {
String content = EntityUtils.toString(response.getEntity(), "UTF-8");
System.out.println(content);
}
} finally {
if (response != null) {
response.close();
}
httpclient.close();
}

}

}

封装HttpClient通用工具类

public class HttpClientUtil {

public static String doGet(String url, Map<String, String> param) {

// 创建Httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();

String resultString = "";
CloseableHttpResponse response = null;
try {
// 创建uri
URIBuilder builder = new URIBuilder(url);
if (param != null) {
for (String key : param.keySet()) {
builder.addParameter(key, param.get(key));
}
}
URI uri = builder.build();

// 创建http GET请求
HttpGet httpGet = new HttpGet(uri);

// 执行请求
response = httpclient.execute(httpGet);
// 判断返回状态是否为200
if (response.getStatusLine().getStatusCode() == 200) {
resultString = EntityUtils.toString(response.getEntity(), "UTF-8");
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (response != null) {
response.close();
}
httpclient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return resultString;
}

public static String doGet(String url) {
return doGet(url, null);
}

public static String doPost(String url, Map<String, String> param) {
// 创建Httpclient对象
CloseableHttpClient httpClient = HttpClients.createDefault();
CloseableHttpResponse response = null;
String resultString = "";
try {
// 创建Http Post请求
HttpPost httpPost = new HttpPost(url);
// 创建参数列表
if (param != null) {
List<NameValuePair> paramList = new ArrayList<>();
for (String key : param.keySet()) {
paramList.add(new BasicNameValuePair(key, param.get(key)));
}
// 模拟表单
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList);
httpPost.setEntity(entity);
}
// 执行http请求
response = httpClient.execute(httpPost);
resultString = EntityUtils.toString(response.getEntity(), "utf-8");
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
response.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

return resultString;
}

public static String doPost(String url) {
return doPost(url, null);
}
}