什么是httpclient

时间 2019-11-19

原文原文链接

1.

1.1. 什么是httpclient

HTTP 协议多是如今 Internet 上使用得最多、最重要的协议了，愈来愈多的 Java 应用程序须要直接经过 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，可是对于大部分应用程序来讲，JDK 库自己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，而且它支持 HTTP 协议最新的版本和建议。
下载地址：html

http://hc.apache.org/java

1.2. 功能介绍

如下列出的是 HttpClient 提供的主要的功能，要知道更多详细的功能能够参见 HttpClient 的主页。apache

（1）实现了全部 HTTP 的方法（GET,POST,PUT,HEAD 等）编程

（2）支持自动转向服务器

（3）支持 HTTPS 协议网络

（4）支持代理服务器等工具

1.3. 导入依赖

1.4. 执行GET请求

public class DoGET {

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

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

        // 建立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();
        }

    }

}

1.5. 执行GET带参数

public class DoGETParam {

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

        // 建立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);

        // 建立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();
        }

    }

}

1.6. 执行post请求

public class DoPOST {

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

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

        // 建立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();
        }

    }

}

1.7. 带参数的post请求

public class DoPOSTParam {

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

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

        // 建立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();
        }

    }

}

1.8. 封装HttpClient通用工具类

public class HttpClientUtil {

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

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

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

			// 建立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) {
		// 建立Httpclient对象
		CloseableHttpClient httpClient = HttpClients.createDefault();
		CloseableHttpResponse response = null;
		String resultString = "";
		try {
			// 建立Http Post请求
			HttpPost httpPost = new HttpPost(url);
			// 建立参数列表
			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);
	}
}

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