如何使用HttpClient

一、简介

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。HttpClient已经应用在很多的项目中，比如Apache Jakarta上很著名的另外两个开源项目Cactus和HTMLUnit都使用了HttpClient。

二、特性

1. 基于标准、纯净的java语言。实现了Http1.0和Http1.1

2. 以可扩展的面向对象的结构实现了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。

3. 支持HTTPS协议。

4. 通过Http代理建立透明的连接。

5. 利用CONNECT方法通过Http代理建立隧道的https连接。

6. Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO/Kerberos认证方案。

7. 插件式的自定义认证方案。

8. 便携可靠的套接字工厂使它更容易的使用第三方解决方案。

9. 连接管理器支持多线程应用。支持设置最大连接数，同时支持设置每个主机的最大连接数，发现并关闭过期的连接。

10. 自动处理Set-Cookie中的Cookie。

11. 插件式的自定义Cookie策略。

12. Request的输出流可以避免流中内容直接缓冲到socket服务器。

13. Response的输入流可以有效的从socket服务器直接读取相应内容。

14. 在http1.0和http1.1中利用KeepAlive保持持久连接。

15. 直接获取服务器发送的response code和 headers。

16. 设置连接超时的能力。

17. 实验性的支持http1.1 response caching。

18. 源代码基于Apache License 可免费获取。

三、使用方法

使用HttpClient发送请求、接收响应很简单，一般需要如下几步即可。

1. 创建HttpClient对象。

2. 创建请求方法的实例，并指定请求URL。如果需要发送GET请求，创建HttpGet对象；如果需要发送POST请求，创建HttpPost对象。

3. 如果需要发送请求参数，可调用HttpGet、HttpPost共同的setParams(HetpParams params)方法来添加请求参数；对于HttpPost对象而言，也可调用setEntity(HttpEntity entity)方法来设置请求参数。

4. 调用HttpClient对象的execute(HttpUriRequest request)发送请求，该方法返回一个HttpResponse。

5. 调用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可获取服务器的响应头；调用HttpResponse的getEntity()方法可获取HttpEntity对象，该对象包装了服务器的响应内容。程序可通过该对象获取服务器的响应内容。

6. 释放连接。无论执行方法是否成功，都必须释放连接

package com.test

import java.io.File

import java.io.FileInputStream

import java.io.IOException

import java.io.UnsupportedEncodingException

import java.security.KeyManagementException

import java.security.KeyStore

import java.security.KeyStoreException

import java.security.NoSuchAlgorithmException

import java.security.cert.CertificateException

import java.util.ArrayList

import java.util.List

import javax.net.ssl.SSLContext

import org.apache.http.HttpEntity

import org.apache.http.NameValuePair

import org.apache.http.ParseException

import org.apache.http.client.ClientProtocolException

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.conn.ssl.SSLConnectionSocketFactory

import org.apache.http.conn.ssl.SSLContexts

import org.apache.http.conn.ssl.TrustSelfSignedStrategy

import org.apache.http.entity.ContentType

import org.apache.http.entity.mime.MultipartEntityBuilder

import org.apache.http.entity.mime.content.FileBody

import org.apache.http.entity.mime.content.StringBody

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

import org.junit.Test

public class HttpClientTest {

@Test

public void jUnitTest() {

get()

}

/**

* HttpClient连接SSL

*/

public void ssl() {

CloseableHttpClient httpclient = null

try {

KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType())

FileInputStream instream = new FileInputStream(new File("d:\\tomcat.keystore"))

try {

// 加载keyStore d:\\tomcat.keystore

trustStore.load(instream, "123456".toCharArray())

} catch (CertificateException e) {

e.printStackTrace()

} finally {

try {

instream.close()

} catch (Exception ignore) {

}

}

// 相信自己的CA和所有自签名的证书

SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build()

// 只允许使用TLSv1协议

SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[] { "TLSv1" }, null,

SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER)

httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build()

// 创建http请求(get方式)

HttpGet httpget = new HttpGet("https://localhost:8443/myDemo/Ajax/serivceJ.action")

System.out.println("executing request" + httpget.getRequestLine())

CloseableHttpResponse response = httpclient.execute(httpget)

try {

HttpEntity entity = response.getEntity()

System.out.println("----------------------------------------")

System.out.println(response.getStatusLine())

if (entity != null) {

System.out.println("Response content length: " + entity.getContentLength())

System.out.println(EntityUtils.toString(entity))

EntityUtils.consume(entity)

}

} finally {

response.close()

}

} catch (ParseException e) {

e.printStackTrace()

} catch (IOException e) {

e.printStackTrace()

} catch (KeyManagementException e) {

e.printStackTrace()

} catch (NoSuchAlgorithmException e) {

e.printStackTrace()

} catch (KeyStoreException e) {

e.printStackTrace()

} finally {

if (httpclient != null) {

try {

httpclient.close()

} catch (IOException e) {

e.printStackTrace()

}

}

}

}

/**

* post方式提交表单（模拟用户登录请求）

*/

public void postForm() {

// 创建默认的httpClient实例.

CloseableHttpClient httpclient = HttpClients.createDefault()

// 创建httppost

HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action")

// 创建参数队列

List<namevaluepair>formparams = new ArrayList<namevaluepair>()

formparams.add(new BasicNameValuePair("username", "admin"))

formparams.add(new BasicNameValuePair("password", "123456"))

UrlEncodedFormEntity uefEntity

try {

uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8")

httppost.setEntity(uefEntity)

System.out.println("executing request " + httppost.getURI())

CloseableHttpResponse response = httpclient.execute(httppost)

try {

HttpEntity entity = response.getEntity()

if (entity != null) {

System.out.println("--------------------------------------")

System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"))

System.out.println("--------------------------------------")

}

} finally {

response.close()

}

} catch (ClientProtocolException e) {

e.printStackTrace()

} catch (UnsupportedEncodingException e1) {

e1.printStackTrace()

} catch (IOException e) {

e.printStackTrace()

} finally {

// 关闭连接,释放资源

try {

httpclient.close()

} catch (IOException e) {

e.printStackTrace()

}

}

}

/**

* 发送 post请求访问本地应用并根据传递参数不同返回不同结果

*/

public void post() {

// 创建默认的httpClient实例.

CloseableHttpClient httpclient = HttpClients.createDefault()

// 创建httppost

HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action")

// 创建参数队列

List<namevaluepair>formparams = new ArrayList<namevaluepair>()

formparams.add(new BasicNameValuePair("type", "house"))

UrlEncodedFormEntity uefEntity

try {

uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8")

httppost.setEntity(uefEntity)

System.out.println("executing request " + httppost.getURI())

CloseableHttpResponse response = httpclient.execute(httppost)

try {

HttpEntity entity = response.getEntity()

if (entity != null) {

System.out.println("--------------------------------------")

System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"))

System.out.println("--------------------------------------")

}

} finally {

response.close()

}

} catch (ClientProtocolException e) {

e.printStackTrace()

} catch (UnsupportedEncodingException e1) {

e1.printStackTrace()

} catch (IOException e) {

e.printStackTrace()

} finally {

// 关闭连接,释放资源

try {

httpclient.close()

} catch (IOException e) {

e.printStackTrace()

}

}

}

/**

* 发送 get请求

*/

public void get() {

CloseableHttpClient httpclient = HttpClients.createDefault()

try {

// 创建httpget.

HttpGet httpget = new HttpGet("具体的网址")

System.out.println("executing request " + httpget.getURI())

// 执行get请求.

CloseableHttpResponse response = httpclient.execute(httpget)

try {

// 获取响应实体

HttpEntity entity = response.getEntity()

System.out.println("--------------------------------------")

// 打印响应状态

System.out.println(response.getStatusLine())

if (entity != null) {

// 打印响应内容长度

System.out.println("Response content length: " + entity.getContentLength())

// 打印响应内容

System.out.println("Response content: " + EntityUtils.toString(entity))

}

System.out.println("------------------------------------")

} finally {

response.close()

}

} catch (ClientProtocolException e) {

e.printStackTrace()

} catch (ParseException e) {

e.printStackTrace()

} catch (IOException e) {

e.printStackTrace()

} finally {

// 关闭连接,释放资源

try {

httpclient.close()

} catch (IOException e) {

e.printStackTrace()

}

}

}

/**

* 上传文件

*/

public void upload() {

CloseableHttpClient httpclient = HttpClients.createDefault()

try {

HttpPost httppost = new HttpPost("http: //localhost:8080/myDemo/Ajax/serivceFile.action")

FileBody bin = new FileBody(new File("F:\\image\\sendpix0.jpg"))

StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN)

HttpEntity reqEntity = MultipartEntityBuilder.create().addPart("bin", bin).addPart("comment", comment).build()

httppost.setEntity(reqEntity)

System.out.println("executing request " + httppost.getRequestLine())

CloseableHttpResponse response = httpclient.execute(httppost)

try {

System.out.println("----------------------------------------")

System.out.println(response.getStatusLine())

HttpEntity resEntity = response.getEntity()

if (resEntity != null) {

System.out.println("Response content length: " + resEntity.getContentLength())

}

EntityUtils.consume(resEntity)

} finally {

response.close()

}

} catch (ClientProtocolException e) {

e.printStackTrace()

} catch (IOException e) {

e.printStackTrace()

} finally {

try {

httpclient.close()

} catch (IOException e) {

e.printStackTrace()

}

}

}

}</namevaluepair></namevaluepair></namevaluepair></namevaluepair>

由于HttpClient内置支持HTTPBasic认证方式，因而使用HttpClient通过HTTPBasic认证的步骤显得较为简单。

1.为HttpClient的状态对象添加用户名/密码对。可以注意到在setCredentials方法中的另一个参数为AuthScope对象。事实上我们添加的每个用户名/密码对都与一个AuthScope对象相关联。AuthScope对象确定了此用户名/密码对的适用站点，在示例中所给出的用户名/密码对将只适用于www.sample.com位于80端口上的资源。HttpClient在与其他站点交互时将不会使用此用户名/密码对，这样有效地防止了机密数据被传送至不必要的站点。

2.开启HttpClient提供的占先式（Preemptive）认证功能。开启了这个功能后，HttpClient对于那些处在之前请求过的URI空间范围内的资源，会主动地随请求一起向服务器发送Basic认证数据，而不是等待服务器返回是否需要认证的响应后再提交认证。在多数情况下，能够减少请求-响应传递的次数，从而间接提高了服务器的响应能力。值得注意的是在这种情况下必须在AuthScope对象中明确指定适用站点，以避免向不相关的站点泄漏敏感数据。3.创建GetMethod对象，此对象将使用GET方式对保护资源发出HTTP请求。

4.setDoAuthentication(true)语句将告知HttpClient在服务器端发回需要认证的请求后，自动将我们在步骤1中设置的用户名/密码对发送至服务器，以完成认证过程。

5.执行GET请求，获取和处理受保护资源的内容。

4种为HttpClient添加默认请求头的方式。下面详细的介绍；

第一种方式

直接在创建的HttpClient对象的DefaultRequestHeaders集合中添加报头。

class Program

{undefined

static Task Main()=>SendAsync1()

private static async Task SendAsync1()

{undefined

var httpClient = new HttpClient()

AddDefaultHeaders(httpClient)

await httpClient.GetStringAsync("http://localhost:5000/")

}

private static void AddDefaultHeaders(HttpClient httpClient)

{undefined

httpClient.DefaultRequestHeaders.Add("x-www-foo", "123")

httpClient.DefaultRequestHeaders.Add("x-www-bar", "456")

httpClient.DefaultRequestHeaders.Add("x-www-baz", "789")

}

}

第二种方式

对于.NET Core应用来说，我们更推荐的做法是采用依赖注入的方式，利用IHttpClientFactory来创建HttpClient对象，那么我们在进行相关服务注册的时候就可以设置默认请求报头。

class Program

{undefined

static Task Main()=>SendAsync2()

private static async Task SendAsync2()

{undefined

var services = new ServiceCollection()

services.AddHttpClient("", AddDefaultHeaders)

var httpClient = services

.BuildServiceProvider()

.GetRequiredService()

.CreateClient()

await httpClient.GetStringAsync("http://localhost:5000/")

}

private static void AddDefaultHeaders(HttpClient httpClient)

{undefined

httpClient.DefaultRequestHeaders.Add("x-www-foo", "123")

httpClient.DefaultRequestHeaders.Add("x-www-bar", "456")

httpClient.DefaultRequestHeaders.Add("x-www-baz", "789")

}

}

第三种方式

由于HttpClient在发送请求的时候会利用DiagnosticSource对象发送相应的诊断事件，并且将作为请求的HttpRequestMessage对象作为请求事件内容负载。我们可以订阅该事件，在请求被发送之前将其拦截下来，并添加相应的请求头即可。

class Program

{undefined

static Task Main()=>SendAsync3()

private static async Task SendAsync3()

{undefined

Func requestAccessor = null

DiagnosticListener.AllListeners.Subscribe(listener =>

{undefined

if (listener.Name == "HttpHandlerDiagnosticListener")

{undefined

listener.Subscribe(kv =>

{undefined

if (kv.Key == "System.Net.Http.HttpRequestOut.Start")

{undefined

requestAccessor ??= BuildRequestAccessor(kv.Value.GetType())

var request = requestAccessor(kv.Value)

AddDefaultHeaders(request)

}

})

}

})

var httpClient = new HttpClient()

await httpClient.GetStringAsync("http://localhost:5000/")

static Func BuildRequestAccessor(Type payloadType)

{undefined

var property = payloadType.GetProperty("Request", BindingFlags.Instance | BindingFlags.Public)

var payload = Expression.Parameter(typeof(object))

var convertedPayload = Expression.Convert(payload, payloadType)

var getRequest = Expression.Call(convertedPayload, property.GetMethod)

var convert = Expression.Convert(getRequest, typeof(HttpRequestMessage))

return Expression.Lambda>(convert, payload).Compile()

}

}

private static void AddDefaultHeaders(HttpRequestMessage request)

{undefined

request.Headers.Add("x-www-foo", "123")

request.Headers.Add("x-www-bar", "456")

request.Headers.Add("x-www-baz", "789")

}

}

第四种方式

上面这种方式可以采用强类型编程方式，具体的代码如下。

class Program

{undefined

static Task Main()=>SendAsync4()

private static async Task SendAsync4()

{undefined

DiagnosticListener.AllListeners.Subscribe(listener =>

{undefined

if (listener.Name == "HttpHandlerDiagnosticListener")

{undefined

listener.SubscribeWithAdapter(new HttpClientListener())

}

})

var httpClient = new HttpClient()

await httpClient.GetStringAsync("http://localhost:5000/")

}

private sealed class HttpClientListener

{undefined

[DiagnosticName("System.Net.Http.HttpRequestOut.Start")]

public void OnSend(HttpRequestMessage request) =>AddDefaultHeaders(request)

//Must subscribute the System.Net.Http.HttpRequestOut event.

[DiagnosticName("System.Net.Http.HttpRequestOut")]

public void OnSend() { }

}

private static void AddDefaultHeaders(HttpRequestMessage request)

{undefined

request.Headers.Add("x-www-foo", "123")

request.Headers.Add("x-www-bar", "456")

request.Headers.Add("x-www-baz", "789")

}

}

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