关于Python中的"HttpClient"，可以参考《爬虫及其Python实现：1.发送请求获取响应》。

简介

在Java中，HttpClient，一般指的指Apache的那一款HttpClient。
官网：http://hc.apache.org

迄今为止，HttpClient有三个大版本：

commons-httpclient是3版本及之前的。
org.apache.httpcomponents是4版本的。
org.apache.httpcomponents.client5是5版本的，

在本章，我们以使用最多的4版本为例。

原生方式

除了HttpClient，JDK本身当然也支持发HTTP请求。我们简单的举一个JDK的原生方式。

示例代码：

package com.kakawanyifan;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.nio.charset.StandardCharsets;

public class Raw {
    public static void main(String[] args) throws IOException {
        // 需要请求的地址
        String urlString = "https://kakawanyifan.com";
        // 把字符串转成URL
        URL url = new URL(urlString);
        // 通过URL对象打开连接
        URLConnection urlConnection = url.openConnection();
        // 强制转换为HttpURLConnection
        HttpURLConnection httpURLConnection = (HttpURLConnection) urlConnection;
        // 获取输入流
        InputStream inputStream = httpURLConnection.getInputStream();

        InputStreamReader inputStreamReader = new InputStreamReader(inputStream, StandardCharsets.UTF_8);
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
        String line;
        while ((line = bufferedReader.readLine()) != null){
            System.out.println(line);
        }
    }
}

运行结果：

<!DOCTYPE html><html lang="zh-CN" data-theme="light"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width,initial-scale=1"><title>Kaka Wan Yifan</title><meta name="description" content=""><meta name="author" content="Kaka Wan Yifan,i@m.kakawanyifan.com"><meta name="copyright" content="Kaka Wan Yifan"><meta name="format-detection" content="telephone=no"><link rel="shortcut icon" href="/img/favicon.ico"><meta http-equiv="Cache-Control" content="no-transform"><meta http-equiv="Cache-Control" content="no-siteapp"><link rel="preconnect" href="//cdn.jsdelivr.net"/><link rel="preconnect" href="https://fonts.googleapis.com" crossorigin="crossorigin"/><meta name="google-site-verification" content="SzZHj5G5vHwv9JUmJD-bxmThc7a6YoZAsaNhwcD-BmM"/><meta name="msvalidate.01" content="1DD984606A0A3BC45A692A32685321AB"/><meta name="baidu-site-verification" content="99Pgg3yv8a"/><meta name="360-site-verification" content="273e85da5f4d732881979af78473b941"/><meta name="twitter:card" content="summary"><meta name="twitter:title" content="Kaka Wan Yifan"><meta name="twitter:description" content=""><meta name="twitter:image" content="https://kakawanyifan.com/img/avatar.jpg"><meta property="og:type" content="website"><meta property="og:title" content="Kaka Wan Yifan"><meta property="og:url" content="https://kakawanyifan.com/"><meta property="og:site_name" content="Kaka Wan Yifan"><meta property="og:description" content=""><meta property="og:image" content="https://kakawanyifan.com/img/avatar.jpg"><script src="//unpkg.com/js-cookie/dist/js.cookie.min.js"></script><script>var autoChangeMode = 'false'
var t = Cookies.get("theme")
if (autoChangeMode == '1'){
  var isDarkMode = window.matchMedia("(prefers-color-scheme: dark)").matches
  var isLightMode = window.matchMedia("(prefers-color-scheme: light)").matches

【部分运行结果略】

  mermaid.initialize({
      theme: 'default',
  })
})
}</script></body></html>

JDK原生的方式，也支持做更多设置，例如：

代理：url.openConnection(【代理】);
请求方法：httpURLConnection.setRequestMethod();
请求头：httpURLConnection.setRequestProperty();
超时时间：
- httpURLConnection.setConnectTimeout();
- httpURLConnection.setReadTimeout();

Get

引入JAR包

首先，我们需要引入HttpClient的JAR包，POM坐标如下：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
</dependency>

无参

我们以最简单的无参的Get请求为例，列举：

发请求的过程
获取响应状态码
获取响应头
获取响应体

package com.kakawanyifan;

import org.apache.http.Header;
import org.apache.http.HttpEntity;
import org.apache.http.StatusLine;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;
import java.nio.charset.StandardCharsets;

public class Get {
    public static void main(String[] args) throws IOException {
        // 创建http客户端
        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        // 创建get对象
        String urlString = "https://kakawanyifan.com";
        HttpGet httpGet = new HttpGet(urlString);
        // 执行请求，获取响应体
        CloseableHttpResponse closeableHttpResponse = closeableHttpClient.execute(httpGet);

        // 获取状态码
        StatusLine statusLine = closeableHttpResponse.getStatusLine();
        System.out.println("状态码：" + statusLine.getStatusCode());

        // 获取响应头
        Header[] allHeaders = closeableHttpResponse.getAllHeaders();
        for (Header header: allHeaders) {
            System.out.println("响应头：" + header.getName() + ":" + header.getValue());
        }

        // 获取响应体
        HttpEntity entity = closeableHttpResponse.getEntity();
        System.out.println("响应体：");
        System.out.println(EntityUtils.toString(entity, StandardCharsets.UTF_8));
        // 确保关闭
        EntityUtils.consume(entity);

        if (null != closeableHttpResponse){
            closeableHttpResponse.close();
        }

        if (null != closeableHttpClient){
            closeableHttpClient.close();
        }
    }
}

运行结果：

状态码：200
响应头：X-Powered-By:Hexo
响应头：Content-Type:text/html
响应头：Date:Tue, 22 Nov 2022 00:28:11 GMT
响应头：Connection:keep-alive
响应头：Keep-Alive:timeout=5
响应头：Transfer-Encoding:chunked
响应体：
<!DOCTYPE html><html lang="zh-CN" data-theme="light"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width,initial-scale=1"><title>Kaka Wan Yifan</title><meta name="description" content=""><meta name="author" content="Kaka Wan Yifan,i@m.kakawanyifan.com"><meta name="copyright" content="Kaka Wan Yifan"><meta name="format-detection" content="telephone=no"><link rel="shortcut icon" href="/img/favicon.ico"><meta http-equiv="Cache-Control" content="no-transform"><meta http-equiv="Cache-Control" content="no-siteapp"><link rel="preconnect" href="//cdn.jsdelivr.net"/><link rel="preconnect" href="https://fonts.googleapis.com" crossorigin="crossorigin"/><meta name="google-site-verification" content="SzZHj5G5vHwv9JUmJD-bxmThc7a6YoZAsaNhwcD-BmM"/><meta name="msvalidate.01" content="1DD984606A0A3BC45A692A32685321AB"/><meta name="baidu-site-verification" content="99Pgg3yv8a"/><meta name="360-site-verification" content="273e85da5f4d732881979af78473b941"/><meta name="twitter:card" content="summary"><meta name="twitter:title" content="Kaka Wan Yifan"><meta name="twitter:description" content=""><meta name="twitter:image" content="https://kakawanyifan.com/img/avatar.jpg"><meta property="og:type" content="website"><meta property="og:title" content="Kaka Wan Yifan"><meta property="og:url" content="https://kakawanyifan.com/"><meta property="og:site_name" content="Kaka Wan Yifan"><meta property="og:description" content=""><meta property="og:image" content="https://kakawanyifan.com/img/avatar.jpg"><script src="//unpkg.com/js-cookie/dist/js.cookie.min.js"></script><script>var autoChangeMode = 'false'
var t = Cookies.get("theme")
if (autoChangeMode == '1'){
  var isDarkMode = window.matchMedia("(prefers-color-scheme: dark)").matches
  var isLightMode = window.matchMedia("(prefers-color-scheme: light)").matches

【部分运行结果略】

  mermaid.initialize({
      theme: 'default',
  })
})
}</script></body></html>

HttpEntity不仅可以作为返回结果，还可以作为请求参数。
在判断HTTP状态码的时候，可以直接利用org.apache.http.HttpStatus的预置好的常量。
例如：
1
2
3
if (HttpStatus.SC_OK == statusLine.getStatusCode()){

}
获取Content-Type，除了通过Headers获取，还可以通过响应体获取。
1
entity.getContentType();

有参

服务端

假设存在一个后台应用，代码如下：

package com.kakawanyifan;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Enumeration;

@WebServlet("/request")
public class RequestDemo extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) {

        Enumeration<String> parameterNames = req.getParameterNames();
        while (parameterNames.hasMoreElements()) {
            String key = parameterNames.nextElement();
            System.out.println(key + ":");
            System.out.println(req.getParameter(key));
        }
    }
}

客户端

现在，我们要以Get请求的方式传递参数。

把参数以如下的格式拼接在URL上即可

1	?【参数名-1】=【参数值-1】&【参数名-2】=【参数值-2】

示例代码：

package com.kakawanyifan;

import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.IOException;

public class Get {
    public static void main(String[] args) throws IOException {
        // 创建http客户端
        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        // 创建get对象
        String urlString = "http://localhost:8080/hcs/request";
        urlString = urlString + "?" + "u=123";
        System.out.println(urlString);
        HttpGet httpGet = new HttpGet(urlString);
        // 执行请求，获取响应体
        closeableHttpClient.execute(httpGet);

        if (null != closeableHttpClient){
            closeableHttpClient.close();
        }
    }
}

运行结果：

1	http://localhost:8080/hcs/request?u=123

同时，我们会看到后台应用有打印日志：

1
2

u:
123

假如，我们传递的有中文呢？
例如，http://localhost:8080/hcs/request?u=中文字符。
这也没问题，后台应用打印的日志如下：

1
2

u:
中文字符

(在《13.Servlet、Filter和Listener》，我们讨论的Get请求中的乱码的时候，提到过：8版本的Tomcat的默认配置中，已经不会复现了。)

URLEncode

但，如果有特殊符号呢？
例如，http://localhost:8080/hcs/request?u=中文字符&p=1+2+3。
后台应用打印的日志如下：

u:
中文字符
p:
1 2 3

+号没了？

这是因为对于特殊字符，我们需要做urlencode。

示例代码：

String urlString = "http://localhost:8080/hcs/request";
urlString = urlString + "?";
urlString = urlString + "u=" + URLEncoder.encode("中文字符", StandardCharsets.UTF_8.name());
urlString = urlString + "&";
urlString = urlString + "p=" + URLEncoder.encode("1+2+3", StandardCharsets.UTF_8.name());

后台打印：

u:
中文字符
p:
1+2+3

保存网络图片到本地

现在存在一张图片，地址如下：
https://kakawanyifan.com/img/avatar.jpg

现在，我们要保存网络图片到本地。
方法是，将响应体转为字节流，并写入文件。

示例代码：

package com.kakawanyifan;

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.FileOutputStream;
import java.io.IOException;

public class Get {
    public static void main(String[] args) throws IOException {
        // 创建http客户端
        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        // 创建get对象
        String urlString = "https://kakawanyifan.com/img/avatar.jpg";

        HttpGet httpGet = new HttpGet(urlString);
        // 执行请求，获取响应体
        CloseableHttpResponse closeableHttpResponse = closeableHttpClient.execute(httpGet);
        // 获取响应体
        HttpEntity httpEntity = closeableHttpResponse.getEntity();

        // 获取Content-Type的值
        String contentTypeValue = httpEntity.getContentType().getValue();

        String suffix = ".jpg";
        if (contentTypeValue.contains("jpg") || contentTypeValue.contains("jpeg")) {
            suffix = ".jpg";
        } else if (contentTypeValue.contains("bmp") || contentTypeValue.contains("bitmap")) {
            suffix = ".bmp";
        } else if (contentTypeValue.contains("png")) {
            suffix = ".png";
        } else if (contentTypeValue.contains("gif")) {
            suffix = ".gif";
        }

        // 获取文件字节流
        byte[] bytes = EntityUtils.toByteArray(httpEntity);
        String filePath = "pic" + suffix;
        FileOutputStream fileOutputStream = new FileOutputStream(filePath);
        fileOutputStream.write(bytes);
        fileOutputStream.close();
    }
}

设置访问代理

假设我们现在访问一个地址，该地址的访问受限，需要通过代码才能访问。

没有代理的情况，示例代码：

package com.kakawanyifan;

import org.apache.http.StatusLine;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import java.io.IOException;

public class Get {
    public static void main(String[] args) throws IOException {
        // 创建http客户端
        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        // 创建get对象
        String urlString = "【受限地址】";
        
        HttpGet httpGet = new HttpGet(urlString);
        // 执行请求，获取响应
        CloseableHttpResponse closeableHttpResponse = closeableHttpClient.execute(httpGet);
        
        // 获取状态码
        StatusLine statusLine = closeableHttpResponse.getStatusLine();
        System.out.println("状态码：" + statusLine.getStatusCode());
        
    }
}

运行结果：

Exception in thread "main" org.apache.http.conn.HttpHostConnectException: Connect to 【受限地址】:443 [【受限地址】/101.230.202.141, 【受限地址】/2408:8026:b0:5d:0:0:0:2] failed: Connection timed out: connect

【部分运行结果略】

Caused by: java.net.ConnectException: Connection timed out: connect

【部分运行结果略】

添加代理，示例代码：

HttpHost proxy = new HttpHost(【代理IP】, 【代理端口】);        
RequestConfig requestConfig = RequestConfig.custom().setProxy(proxy).build();

httpGet.setConfig(requestConfig);

运行结果：

状态码：200

设置超时时间

在上文，我们看到没有代理的时候，报错是Connection timed out: connect。
HttpClient的默认超时时间是30秒，我们也可以自定义超时时间。

超时时间一共有3种：

.setConnectTimeout：连接超时，单位ms，指完成tcp的3次握手的时间。
.setSocketTimeout：读取超时，单位ms，表示从请求的地址获取响应的时间间隔。
.setConnectionRequestTimeout：从连接池获取connection的超时时间

示例代码：

// 设置超时时间
RequestConfig requestConfig = RequestConfig.custom()
        // 连接超时，单位ms，指完成tcp的3次握手的时间
        .setConnectTimeout(5000)
        // 读取超时，单位ms，表示从请求的地址获取响应的时间间隔
        .setSocketTimeout(5000)
        // 从连接池获取connection的超时时间
        .setConnectionRequestTimeout(5000)
        .build();
httpGet.setConfig(requestConfig);

设置请求头

有时候，如果我们需要反爬，或者想防止被防盗链的话，设置请求头会有些作用。

// 设置User-Agent，伪装成浏览器
httpGet.addHeader("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.141 Safari/537.36");
// 防止被防盗链
httpGet.addHeader("Referer","https://www.baidu.com/");

上述的很多例子，对于Post请求，同样适用。

Post

常见的Post请求有3种：

application/x-www-form-urlencoded
以表单的形式提交。
application/json
以JSON的形式提交。
multipart/form-data
上传文件。

application/x-www-form-urlencoded

application/x-www-form-urlencoded，以表单的形式提交。

服务端

假设存在后端应用如下：

package com.kakawanyifan;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.Enumeration;

@WebServlet("/request")
public class RequestDemo extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
        Enumeration<String> headerNames = req.getHeaderNames();
        while (headerNames.hasMoreElements()) {
            String key = headerNames.nextElement();
            System.out.println(key + " : " + req.getHeader(key));
        }

        Enumeration<String> parameterNames = req.getParameterNames();
        while (parameterNames.hasMoreElements()) {
            String key = parameterNames.nextElement();
            System.out.println(key + " : " + req.getParameter(key));
        }
    }
}

web.xml文件的内容如下：

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
</web-app>

客户端

表单方式提交，主要利用NameValuePair和UrlEncodedFormEntity。

示例代码：

package com.kakawanyifan;

import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
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 java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;

public class Post {
    public static void main(String[] args) throws IOException {

        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        String urlString = "http://localhost:8080/hcs/request";
        HttpPost httpPost = new HttpPost(urlString);

        List<NameValuePair> nameValuePairList = new ArrayList<>();
        nameValuePairList.add(new BasicNameValuePair("u", "中文字符"));
        nameValuePairList.add(new BasicNameValuePair("p", "1+2+3"));
        UrlEncodedFormEntity urlEncodedFormEntity = new UrlEncodedFormEntity(nameValuePairList, StandardCharsets.UTF_8);
        httpPost.setEntity(urlEncodedFormEntity);

        closeableHttpClient.execute(httpPost);

        if (null != closeableHttpClient) {
            closeableHttpClient.close();
        }

    }
}

我们会看到后台服务打印日志：

content-length : 50
content-type : application/x-www-form-urlencoded; charset=UTF-8
host : localhost:8080
connection : Keep-Alive
user-agent : Apache-HttpClient/4.5.13 (Java/1.8.0_333)
accept-encoding : gzip,deflate
u : 中文字符
p : 1+2+3

挺正常的，没啥问题，中文也没乱码。

在《13.Servlet、Filter和Listener》，我们讨论乱码的时候，我们说： 因为客户端将数据发送给服务端后，并没有告诉服务端需要采取何种编码方式，这时候服务端会采取默认的ISO-8859-1。

在这里，我们的content-type，application/x-www-form-urlencoded; charset=UTF-8，指明了用UTF-8，所以没有乱码。

如果我们将

1	UrlEncodedFormEntity urlEncodedFormEntity = new UrlEncodedFormEntity(nameValuePairList, Consts.UTF_8);

改为

1	UrlEncodedFormEntity urlEncodedFormEntity = new UrlEncodedFormEntity(nameValuePairList);

即去除StandardCharsets.UTF_8，会有乱码。

content-length : 26
content-type : application/x-www-form-urlencoded
host : localhost:8080
connection : Keep-Alive
user-agent : Apache-HttpClient/4.5.13 (Java/1.8.0_333)
accept-encoding : gzip,deflate
u : ????
p : 1+2+3

如果我们用Postman默认的设置发，也有乱码，也是因为没有指明用UTF-8。

此时，后台打印的日志如下：

user-agent : PostmanRuntime/7.28.4
accept : */*
postman-token : 7b5d2c32-fb0c-4d13-b4a1-e6b0d25718b0
host : localhost:8080
accept-encoding : gzip, deflate, br
connection : keep-alive
content-type : application/x-www-form-urlencoded
content-length : 50
u : æ³¾å·ææ±
p : 1+2+3

application/json

application/json，以JSON的形式提交。

服务端

此时，服务端接收方式也要改，需要以"流"的方式读取，而不是在请求体中就直接有了。示例代码：

package com.kakawanyifan;

import com.alibaba.fastjson2.JSONObject;

import javax.servlet.ServletInputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Enumeration;

@WebServlet("/request")
public class RequestDemo extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        Enumeration<String> headerNames = req.getHeaderNames();
        while (headerNames.hasMoreElements()) {
            String key = headerNames.nextElement();
            System.out.println(key + " : " + req.getHeader(key));
        }

        Enumeration<String> parameterNames = req.getParameterNames();
        while (parameterNames.hasMoreElements()) {
            String key = parameterNames.nextElement();
            System.out.println(key + " : " + req.getParameter(key));
        }

        BufferedReader br = new BufferedReader(new InputStreamReader((ServletInputStream) req.getInputStream(), "utf-8"));
        StringBuffer sb = new StringBuffer("");
        String temp;
        while ((temp = br.readLine()) != null) {
            sb.append(temp);
        }
        br.close();

        String json = sb.toString();
        JSONObject jo = JSONObject.parseObject(json);
        System.out.println(jo);
    }
}

上述流的方式，有一种更简洁的写法：

1 2	BufferedReader reader = req.getReader(); String json = reader.readLine();

关于该部分，可以参考我们在《5.IO流》的讨论。

客户端

客户端以JSON的形式提交，主要利用StringEntity.

示例代码：

package com.kakawanyifan;

import com.alibaba.fastjson2.JSONObject;
import org.apache.http.Consts;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.IOException;

public class Post {
    public static void main(String[] args) throws IOException {

        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        String urlString = "http://localhost:8080/hcs/request";
        HttpPost httpPost = new HttpPost(urlString);

        JSONObject jo = new JSONObject();
        jo.put("u","中文字符");
        jo.put("p","1+2+3");

        StringEntity stringEntity = new StringEntity(jo.toString(),Consts.UTF_8);
        httpPost.setEntity(stringEntity);
        closeableHttpClient.execute(httpPost);

        if (null != closeableHttpClient) {
            closeableHttpClient.close();
        }

    }
}

服务端打印：

content-length : 32
content-type : text/plain; charset=UTF-8
host : localhost:8080
connection : Keep-Alive
user-agent : Apache-HttpClient/4.5.13 (Java/1.8.0_333)
accept-encoding : gzip,deflate
{"u":"中文字符","p":"1+2+3"}

注意content-type : text/plain; charset=UTF-8，虽然不影响，但还是建议改掉。

1
2
3

stringEntity.setContentType("application/json; charset=utf-8");
// 设置entity的编码
stringEntity.setContentEncoding(Consts.UTF_8.name());

com.alibaba.fastjson2.JSONObject的引入：

<dependency>
    <groupId>com.alibaba.fastjson2</groupId>
    <artifactId>fastjson2</artifactId>
    <version>2.0.19</version>
</dependency>

multipart/form-data

multipart/form-data，上传文件。

服务端

服务端接收文件的示例代码：

package com.kakawanyifan;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.util.Enumeration;
import java.util.List;

@WebServlet("/request")
public class RequestDemo extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
        Enumeration<String> headerNames = req.getHeaderNames();
        while (headerNames.hasMoreElements()) {
            String key = headerNames.nextElement();
            System.out.println(key + " : " + req.getHeader(key));
        }

        boolean isMultipart = ServletFileUpload.isMultipartContent(req);

        if (isMultipart) {
            DiskFileItemFactory factory = new DiskFileItemFactory();
            String path = getServletContext().getRealPath("/");
            factory.setRepository(new File(path));
            ServletFileUpload servletFileUpload = new ServletFileUpload(factory);

            try {
                // 解析请求，获取文件项
                List<FileItem> fileItemList = servletFileUpload.parseRequest(req);
                for (FileItem fileItem : fileItemList) {
                    System.out.println("fileItem :" + fileItem);
                    if (!fileItem.isFormField()) {
                        // 获取上传文件的参数
                        String fieldName = fileItem.getFieldName();
                        String fileName = fileItem.getName();
                        String contentType = fileItem.getContentType();

                        System.out.println("fieldName : " + fieldName);
                        System.out.println("fileName : " + fileName);
                        System.out.println("contentType : " + contentType);

                        // 写入文件
                        File file = new File(path + fileName);
                        fileItem.write(file);
                    }
                }
            } catch (FileUploadException e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }
}

客户端

客户端通过Post上传文件。

主要利用MultipartEntityBuilder。

示例代码：

package com.kakawanyifan;

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.File;
import java.io.IOException;

public class Post {
    public static void main(String[] args) throws IOException {

        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        String urlString = "http://localhost:8080/hcs/request";
        HttpPost httpPost = new HttpPost(urlString);

        MultipartEntityBuilder multipartEntityBuilder = MultipartEntityBuilder.create();
        multipartEntityBuilder.addBinaryBody("AttachName", new File("pic.jpg"));
        HttpEntity httpEntity = multipartEntityBuilder.build();
        httpPost.setEntity(httpEntity);
        closeableHttpClient.execute(httpPost);

        if (null != closeableHttpClient) {
            closeableHttpClient.close();
        }

    }
}

content-length : 142661
content-type : multipart/form-data; boundary=sapnWb-jKfAsXd1DXLM5lNdOwaWchj
host : localhost:8080
connection : Keep-Alive
user-agent : Apache-HttpClient/4.5.13 (Java/1.8.0_333)
accept-encoding : gzip,deflate
fileItem : name=pic.jpg, StoreLocation=/Users/kaka/Documents/apache-tomcat-8.5.81/webapps/hcs/upload_35ec497b_9b7f_4b1d_8c80_cd465a0cc44f_00000004.tmp, size=142441 bytes, isFormField=false, FieldName=AttachName
fieldName : AttachName
fileName : pic.jpg
contentType : application/octet-stream

绕过不安全的HTTPS

如果HTTPS是安全的，那很简单，直接请求，和我们上文的讨论没有区别。

但如果是不安全的呢？
示例代码：

package com.kakawanyifan;

import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.IOException;

public class Get {

    public static void main(String[] args) throws IOException {
        CloseableHttpClient closeableHttpClient = HttpClients.createDefault();
        String urlString = "【不安全的https地址】";
        HttpGet httpGet = new HttpGet(urlString);
        CloseableHttpResponse closeableHttpResponse = closeableHttpClient.execute(httpGet);
        System.out.println(closeableHttpResponse.getStatusLine().getStatusCode());
    }
}

运行结果：

Exception in thread "main" javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.ssl.Alert.createSSLException(Alert.java:131)

【部分运行结果略】

	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108)
	at com.kakawanyifan.Get.main(Get.java:14)
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:439)
	at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:306)
	at sun.security.validator.Validator.validate(Validator.java:271)
	at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:312)
	at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:221)
	at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:128)
	at sun.security.ssl.CertificateMessage$T12CertificateConsumer.checkServerCerts(CertificateMessage.java:636)
	... 24 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:141)
	at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:126)
	at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:434)
	... 30 more

最常见的方法是：绕过。

重写isTrusted方法，直接返回true。

示例代码：

package com.kakawanyifan;

import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.config.Registry;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.socket.ConnectionSocketFactory;
import org.apache.http.conn.socket.PlainConnectionSocketFactory;
import org.apache.http.conn.ssl.NoopHostnameVerifier;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.BasicHttpClientConnectionManager;
import org.apache.http.ssl.SSLContextBuilder;
import org.apache.http.ssl.TrustStrategy;

import javax.net.ssl.SSLContext;
import java.io.IOException;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;

public class Get {

    /**
     * 构造安全连接工厂
     * @return SSLConnectionSocketFactory
     */
    private static ConnectionSocketFactory trustHttpsCertificates() {
        SSLContextBuilder sslContextBuilder = new SSLContextBuilder();
        try {
            sslContextBuilder.loadTrustMaterial(null, new TrustStrategy() {
                // 判断是否信任url
                @Override
                public boolean isTrusted(X509Certificate[] chain, String authType) throws CertificateException {
                    return true;
                }
            });
            SSLContext sslContext = sslContextBuilder.build();
            return new SSLConnectionSocketFactory(sslContext,
                    new String[]{"SSLv2Hello","SSLv3","TLSv1","TLSv1.1","TLSv1.2"}
                    ,null, NoopHostnameVerifier.INSTANCE);
        } catch (Exception e) {
            throw new RuntimeException("构造安全连接工厂失败");
        }
    }

    public static void main(String[] args) throws IOException {
        Registry<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory>create()
                .register("http", PlainConnectionSocketFactory.INSTANCE)
                .register("https", trustHttpsCertificates())
                .build();
        BasicHttpClientConnectionManager basic = new BasicHttpClientConnectionManager(registry);
        HttpClientBuilder httpClientBuilder = HttpClients.custom().setConnectionManager(basic);
        CloseableHttpClient closeableHttpClient = httpClientBuilder.build();
        String urlString = "【不安全的https】";
        HttpGet httpGet = new HttpGet(urlString);
        CloseableHttpResponse closeableHttpResponse = closeableHttpClient.execute(httpGet);
        System.out.println(closeableHttpResponse.getStatusLine().getStatusCode());
    }
}

运行结果：

连接池和工具类

在上文，我们没有去创建默认的HttpClient，而是用HttpClients.custom().setConnectionManager(basic);去自定义了一个HttpClient。
其中basic，来自BasicHttpClientConnectionManager basic = new BasicHttpClientConnectionManager(registry);。
实际上，除了BasicHttpClientConnectionManager，还有一个PoolingHttpClientConnectionManager，我们可以利用这个，创建连接池。

另外，我们可以把本章的主要代码抽出来，这样我们就了一个工具类。

package com.kakawanyifan;

import org.apache.http.*;
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.config.Registry;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.socket.ConnectionSocketFactory;
import org.apache.http.conn.socket.PlainConnectionSocketFactory;
import org.apache.http.conn.ssl.NoopHostnameVerifier;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.message.BasicHeader;
import org.apache.http.pool.PoolStats;
import org.apache.http.ssl.SSLContextBuilder;
import org.apache.http.ssl.TrustStrategy;
import org.apache.http.util.EntityUtils;

import javax.net.ssl.SSLContext;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.List;
import java.util.Map;
import java.util.Set;


public class HttpClientUtil {
    private static CloseableHttpClient closeableHttpClient;
    private static PoolingHttpClientConnectionManager cm;

    static {
        HttpClientBuilder httpClientBuilder = HttpClients.custom();
        // 绕过不安全的https请求的证书验证
        Registry<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory>create()
                .register("http", PlainConnectionSocketFactory.INSTANCE)
                .register("https", trustHttpsCertificates())
                .build();
        // 创建连接池管理对象
        cm = new PoolingHttpClientConnectionManager(registry);
        // 连接池最大有50个连接
        cm.setMaxTotal(50);
        // 域名(IP)+端口 就是一个路由
        // 每个路由最大有多少连接
        cm.setDefaultMaxPerRoute(50);
        httpClientBuilder.setConnectionManager(cm);

        // 设置超时时间
        RequestConfig requestConfig = RequestConfig.custom()
                .setConnectTimeout(5000)
                .setSocketTimeout(3000)
                .setConnectionRequestTimeout(5000)
                .build();
        httpClientBuilder.setDefaultRequestConfig(requestConfig);

        // 线程安全
        // 此处初始化一次即可
        // 通过上面的配置来生成一个用于管理多个连接的连接池closeableHttpClient
        closeableHttpClient = httpClientBuilder.build();
    }

    /**
     * 构造安全连接工厂
     *
     * @return SSLConnectionSocketFactory
     */
    private static ConnectionSocketFactory trustHttpsCertificates() {
        SSLContextBuilder sslContextBuilder = new SSLContextBuilder();
        try {
            sslContextBuilder.loadTrustMaterial(null, new TrustStrategy() {
                // 判断是否信任url
                @Override
                public boolean isTrusted(X509Certificate[] chain, String authType) throws CertificateException {
                    return true;
                }
            });
            SSLContext sslContext = sslContextBuilder.build();
            return new SSLConnectionSocketFactory(sslContext,
                    new String[]{"SSLv2Hello", "SSLv3", "TLSv1", "TLSv1.1", "TLSv1.2"}
                    , null, NoopHostnameVerifier.INSTANCE);
        } catch (Exception e) {
            throw new RuntimeException("构造安全连接工厂失败");
        }
    }

    /**
     * 发送get请求
     *
     * @param url     请求url,参数需经过URLEncode编码处理
     * @param headers 自定义请求头
     * @return 返回结果
     */
    public static String executeGet(String url, Map<String, String> headers) {
        // 构造httpGet请求对象
        HttpGet httpGet = new HttpGet(url);
        // 自定义请求头设置
        if (headers != null) {
            Set<Map.Entry<String, String>> entries = headers.entrySet();
            for (Map.Entry<String, String> entry : entries) {
                httpGet.addHeader(new BasicHeader(entry.getKey(), entry.getValue()));
            }
        }
        // 可关闭的响应
        CloseableHttpResponse response = null;
        try {
            System.out.println("prepare to execute url:" + url);
            response = closeableHttpClient.execute(httpGet);
            StatusLine statusLine = response.getStatusLine();
            if (HttpStatus.SC_OK == statusLine.getStatusCode()) {
                HttpEntity entity = response.getEntity();
                return EntityUtils.toString(entity, StandardCharsets.UTF_8);
            } else {
                System.err.println(statusLine.getStatusCode());
                HttpEntity entity = response.getEntity();
                return EntityUtils.toString(entity, StandardCharsets.UTF_8);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            consumeRes(response);
        }
        return null;
    }

    /**
     * 发送表单类型的post请求
     *
     * @param url     要请求的url
     * @param list    参数列表
     * @param headers 自定义头
     * @return 返回结果
     */
    public static String postForm(String url, List<NameValuePair> list, Map<String, String> headers) {
        HttpPost httpPost = new HttpPost(url);
        if (headers != null) {
            Set<Map.Entry<String, String>> entries = headers.entrySet();
            for (Map.Entry<String, String> entry : entries) {
                httpPost.addHeader(new BasicHeader(entry.getKey(), entry.getValue()));
            }
        }
        // 确保请求头一定是form类型
        httpPost.addHeader("Content-Type", "application/x-www-form-urlencoded; charset=utf-8");
        // 给post对象设置参数
        UrlEncodedFormEntity formEntity = new UrlEncodedFormEntity(list, Consts.UTF_8);
        httpPost.setEntity(formEntity);
        // 响应处理
        CloseableHttpResponse response = null;
        try {
            System.out.println("prepare to execute url:" + httpPost.getRequestLine());
            response = closeableHttpClient.execute(httpPost);
            StatusLine statusLine = response.getStatusLine();
            if (HttpStatus.SC_OK == statusLine.getStatusCode()) {
                HttpEntity entity = response.getEntity();
                return EntityUtils.toString(entity, StandardCharsets.UTF_8);
            } else {
                System.err.println(statusLine.getStatusCode());
                HttpEntity entity = response.getEntity();
                return EntityUtils.toString(entity, StandardCharsets.UTF_8);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            consumeRes(response);
        }
        return null;
    }

    /**
     * 发送json类型的post请求
     *
     * @param url     请求url
     * @param body    json字符串
     * @param headers 自定义header
     * @return 返回结果
     */
    public static String postJson(String url, String body, Map<String, String> headers) {
        HttpPost httpPost = new HttpPost(url);
        // 设置请求头
        if (headers != null) {
            Set<Map.Entry<String, String>> entries = headers.entrySet();
            for (Map.Entry<String, String> entry : entries) {
                httpPost.addHeader(new BasicHeader(entry.getKey(), entry.getValue()));
            }
        }
        // 确保请求头是json类型
        httpPost.addHeader("Content-Type", "application/json; charset=utf-8");
        /*
        设置请求体
         */
        StringEntity jsonEntity = new StringEntity(body, Consts.UTF_8);
        jsonEntity.setContentType("application/json; charset=utf-8");
        jsonEntity.setContentEncoding(Consts.UTF_8.name());
        httpPost.setEntity(jsonEntity);

        CloseableHttpResponse response = null;
        try {
            response = closeableHttpClient.execute(httpPost);
            StatusLine statusLine = response.getStatusLine();
            if (HttpStatus.SC_OK == statusLine.getStatusCode()) {
                HttpEntity entity = response.getEntity();
                return EntityUtils.toString(entity, StandardCharsets.UTF_8);
            } else {
                System.err.println(statusLine.getStatusCode());
                HttpEntity entity = response.getEntity();
                return EntityUtils.toString(entity, StandardCharsets.UTF_8);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            consumeRes(response);
        }
        return null;
    }

    public static void printStat() {
        // 连接池的最大连接数 50
        System.out.println(cm.getMaxTotal());
        // 每一个路由的最大连接数 50
        System.out.println(cm.getDefaultMaxPerRoute());

        PoolStats totalStats = cm.getTotalStats();
        // 连接池的最大连接数 50
        System.out.println(totalStats.getMax());
        // 连接池里面有多少连接是被占用了
        System.out.println(totalStats.getLeased());
        // 连接池里面有多少连接是可用的
        System.out.println(totalStats.getAvailable());
    }

    private static void consumeRes(CloseableHttpResponse response) {
        // response.close() 是关闭连接,不是归还连接到连接池
        if (response != null) {
            try {
                EntityUtils.consume(response.getEntity());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

setMaxTotal(int max)：Set the maximum number of total open connections
setMaxPerRoute(int max)：Set the total number of concurrent connections to a specific route, which is two by default。

参考资料：

https://www.bilibili.com/video/BV1W54y1s7BZ/

https://blog.csdn.net/w372426096/article/details/82713315

https://blog.csdn.net/CapMiachael/article/details/72930357

https://www.cnblogs.com/284628487a/p/5579936.html

https://www.baeldung.com/httpclient-connection-management

文章作者: Kaka Wan Yifan

文章链接: https://kakawanyifan.com/10814

评论区

简介

原生方式

Get

引入JAR包

无参

有参

服务端

客户端

URLEncode

保存网络图片到本地

设置访问代理

设置超时时间

设置请求头

Post

application/x-www-form-urlencoded

服务端

客户端

application/json

服务端

客户端

multipart/form-data

服务端

客户端

绕过不安全的HTTPS

连接池和工具类​

连接池和工具类