#IT明星不是梦#【从0开始Web开发实战】SpringBoot集成HttpClient，开发进阶

目录：

1. SpringBoot集成HttpClient

2. 封装服务HttpService.java，处理请求参数

3. 封装ResponseHandler<T>，处理返回结果

4. 单元测试

5. 功能调用

6. 常见问题和解决方法

HttpClient是Apache Jakarta Common下的子项目，是一个高效的、功能丰富的HTTP客户端编程工具包，以编程的方式通过API传输和接收HTTP消息。主要功能：

l 支持HTTP方法：GET, POST, PUT, DELETE, HEAD, OPTIONS等

l 支持HTTPS协议

l 支持多线程应用和连接管理，可设置最大连接数

l 支持KeepAlive持久连接

l 支持自定义Cookie策略

l 支持代理服务器：ngnix等

l 支持自动跳转

l ......

本文分享SpringBoot集成和配置HttpClient的方法，并封装HttpService调用请求和ResponseHandler处理返回结果，添加REST接口，演示项目中实际应用。

	代码文件	功能要点
SpringBoot集成HttpClient	pom.xml	引入HttpClient依赖：org.apache.httpcomponents包里的httpclient, httpcore, httpmime
	application.yml	配置HTTP连接属性
	HttpConfig.java	配置Bean: HttpClient，以及RequestConfig和HttpClientConnectionManager
封装服务HttpService	HttpService.java	处理HTTP请求参数，调用HttpClient发送请求
处理返回结果ResponseHandler<T>	RespStr.java RespJsonObj.java RespJsonArr.java RespFile.java	对HttpResponse进行处理，读取HttpEntity并对返回内容进行转换
单元测试	HttpServiceTest.java	测试HttpService发送请求和处理返回结果
功能调用	CheckController.java	增加REST接口/chk/http，发送HTTP请求并返回结果。

代码下载：https://github.com/jextop/StarterApi/

一，SpringBoot集成HttpClient

1. 在pom.xml中添加httpclient, httpcore, httpmime依赖。

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.2</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpcore</artifactId>
    <version>4.4.4</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpmime</artifactId>
    <version>4.5</version>
</dependency>

2. 在application.yml中配置HTTP连接属性，指定最大连接数、超时时间等：

http:
  maxTotal: 100
  maxPerRoute: 20
  socketTimeout: 5000
  connectTimeout: 5000
  requestTimeout: 5000

3. 在HttpConfig.java中配置Bean，读取HTTP连接属性配置，声明RequestConfig和HttpClientConnectionManager，并且创建HttpClient实例：

@Configuration
@ConfigurationProperties("http")
public class HttpConfig {
    private Integer maxTotal;
    private Integer maxPerRoute;
    private Integer socketTimeout;
    private Integer connectTimeout;
    private Integer requestTimeout;

    @Bean
    public HttpClientConnectionManager httpClientConnectionManager() {
        PoolingHttpClientConnectionManager connMgr = new PoolingHttpClientConnectionManager();
        connMgr.setMaxTotal(maxTotal);
        connMgr.setDefaultMaxPerRoute(maxPerRoute);
        return connMgr;
    }

    @Bean
    public RequestConfig requestConfig() {
        return RequestConfig.custom()
                .setSocketTimeout(socketTimeout)
                .setConnectTimeout(connectTimeout)
                .setConnectionRequestTimeout(requestTimeout)
                .build();
    }

    @Bean
    public HttpClient httpClient(HttpClientConnectionManager manager, RequestConfig config) {
        return HttpClientBuilder.create()
                .setConnectionManager(manager)
                .setDefaultRequestConfig(config)
                .build();
    }

}

二，封装服务HttpService.java，处理请求参数，调用HttpClient发送请求。

@Service
public class HttpService {
    @Autowired
    private HttpClient httpClient;

    public <T> T sendRequest(HttpRequestBase httpRequest, ResponseHandler<T> handler) {
        try {
            return httpClient.execute(httpRequest, handler);
        } catch (ClientProtocolException e) {
            LogUtil.error("Error when sendRequest", e.getMessage());
        } catch (IOException e) {
            LogUtil.error("Error when sendRequest", e.getMessage());
        }
        return null;
    }

    public <T> T sendHttpGet(String url, ResponseHandler<T> handler) {
        return sendRequest(new HttpGet(url), handler);
    }

    public String sendHttpGet(String url) {
        return sendHttpGet(url, new RespStr());
    }

    public <T> T sendHttpGet(String url, Map<String, String> headers, ResponseHandler<T> handler) {
        HttpGet httpGet = new HttpGet(url);
        fillHeaders(httpGet, headers);
        return sendRequest(httpGet, handler);
    }

    private static void fillHeaders(HttpRequestBase request, Map<String, String> headers) {
        for (Map.Entry<String, String> header : headers.entrySet()) {
            request.addHeader(header.getKey(), header.getValue());
        }
    }
}

HttpService中使用RespStr处理HttpResponse，返回字符串。

三，封装ResponseHandler<T>，处理返回结果

ResponseHandler<T>是httpclient包内提供的接口，实现函数handleResponse()处理HTTP返回结果，封装处理逻辑。

package org.apache.http.client;

import java.io.IOException;
import org.apache.http.HttpResponse;

public interface ResponseHandler<T> {
    T handleResponse(HttpResponse var1) throws ClientProtocolException, IOException;
}

封装的4个HTTP返回结果处理类，简化逻辑，提高开发效率。

代码文件	HTTP返回结果类型
RespStr.java	返回字符串
RespJsonObj.java	返回JSONObject
RespJsonArr.java	返回JSONArray
RespFile.java	返回二进制文件

1. RespStr.java：读取HttpResponse返回的内容，格式化为String字符串

- 调用httpResponse.getEntiry()获取返回结果

- 调用ContentType.get()获取内容类型

- 调用ContentType.getCharset()获取编码格式

- 调用EntityUtils.toString()将返回结果格式化为字符串

public class RespStr implements ResponseHandler<String> {
    @Override
    public String handleResponse(HttpResponse httpResponse) throws ClientProtocolException, IOException {
        HttpEntity entity = httpResponse.getEntity();
        ContentType contentType = ContentType.getOrDefault(entity);
        Charset charset = contentType.getCharset();
        return EntityUtils.toString(entity, charset);
    }
}

2. RespJsonObj.java：在返回结果为JSON对象时，转换成JSONObject返回

public class RespJsonObj implements ResponseHandler<JSONObject> {
    @Override
    public JSONObject handleResponse(HttpResponse resp) throws ClientProtocolException, IOException {
        HttpEntity entity = resp.getEntity();
        ContentType contentType = ContentType.getOrDefault(entity);
        Charset charset = contentType.getCharset();
        String jsonStr = EntityUtils.toString(entity, charset);

        // parse JSON object
        return JsonUtil.parseObj(jsonStr);
    }
}

3. RespJsonArr.java：将HTTP请求返回结果转换成JSONArray返回

public class RespJsonArr implements ResponseHandler<JSONArray> {
    @Override
    public JSONArray handleResponse(HttpResponse resp) throws ClientProtocolException, IOException {
        HttpEntity entity = resp.getEntity();
        ContentType contentType = ContentType.getOrDefault(entity);
        Charset charset = contentType.getCharset();
        String jsonStr = EntityUtils.toString(entity, charset);

        // parse JSON array
        return JsonUtil.parseArr(jsonStr);
    }
}

4. RespFile.java：在HTTP返回二进制文件时，从Entity中读取二进制内容，并可从Header中获取文件名称。

public class RespFile implements ResponseHandler<byte[]> {
    private static final String fileNameFlag = "attachment;fileName=";

    private byte[] bytes;
    private String fileName;

    public byte[] getBytes() {
        return bytes;
    }

    public String getFileName() {
        return fileName;
    }

    @Override
    public byte[] handleResponse(HttpResponse response) throws ClientProtocolException, IOException {
        // Header: Content-Disposition: attachment;fileName=abc.txt
        Header header = response.getFirstHeader("Content-Disposition");
        String headerValue = header.getValue();
        if (headerValue.startsWith(fileNameFlag)) {
            fileName = headerValue.substring(fileNameFlag.length(), headerValue.length());
        }

        HttpEntity entity = response.getEntity();
        bytes = EntityUtils.toByteArray(entity);
        return bytes;
    }
}

四，单元测试，调用HttpService发送请求和处理返回结果

 

五，功能调用

1. 增加RestController：CheckController.java

2. 增加REST接口/chk/http，发送HTTP请求并返回结果。

@GetMapping(value = "/chk/http", produces = "application/json")
public Object http() {
    String strCourse = httpService.sendHttpGet("https://edu.51cto.com/lecturer/13841865.html");
    String[] courses = StrUtil.parse(strCourse, "[1-9]\\d*人学习");

    return new HashMap<String, Object>() {{
        put("chk", "http");
        put("course", courses);
    }};
}

3. REST接口调用HttpSevice示例

 

六，常见问题和解决方法

l HTTP返回结果乱码，设置UTF-8仍然不能解决？

原因：处理HTTP请求返回结果时，出现乱码是因为设置Charset编码格式不正确，通常设置UTF-8可以解决大部分情况，但并不是所有HTTP服务器都一定使用UTF-8格式。

解决：正确的方法是获取内容编码时的格式：

- 调用httpResponse.getEntiry()获取返回结果

- 调用ContentType.get()获取内容类型

- 调用ContentType.getCharset()获取编码格式

- 调用EntityUtils.toString()将返回结果格式化为字符串

public class RespStr implements ResponseHandler<String> {
    @Override
    public String handleResponse(HttpResponse httpResponse) throws ClientProtocolException, IOException {
        HttpEntity entity = httpResponse.getEntity();
        ContentType contentType = ContentType.getOrDefault(entity);
        Charset charset = contentType.getCharset();
        return EntityUtils.toString(entity, charset);
    }
}

ResponseHandler<T>是httpclient包内提供的接口，实现函数handleResponse()处理HTTP返回结果。