使用CloseableHttpClient 模拟发送HttpGet和HttpPost请求

项目中经常会用到模拟Http请求，而jdk 下的 rt.jar核心库中也有 java.net提供了这方面的功能，但是总体而言，功能还是缺少灵活性和全面性，HttpClient的出现就是弥补了其缺失的功能。HttpClient不是浏览器客户端，而是一个客户端和服务端实现通信的Http组件库。本篇文章主要讲解CloseableHttpClient 的使用。

1. 项目中添加依赖的jar包

        <dependency>
            <groupId>org.apache.httpcomponentsgroupId>
            <artifactId>httpclientartifactId>
            <version>4.5.5version>
            <exclusions>
                <exclusion>
                    <artifactId>commons-codecartifactId>
                    <groupId>commons-codecgroupId>
                exclusion>
            exclusions>
        dependency>

2. 上代码，代码中详细介绍每个部分的作用

2.1 模拟HttpGet请求 

/**
 * 模拟HttpGet 请求
 * @param url
 * @return
 */
public static String HttpGet(String url){
    //单位毫秒
    RequestConfig requestConfig = RequestConfig.custom()
        .setConnectionRequestTimeout(3000).setConnectTimeout(3000)
        .setSocketTimeout(3000).build();//设置请求的状态参数

    CloseableHttpClient httpclient = HttpClients.createDefault();//创建 CloseableHttpClient 
    HttpGet httpGet = new HttpGet(url);
    httpGet.setConfig(requestConfig);

    CloseableHttpResponse response = null;
    try {
        response = httpclient.execute(httpGet);//返回请求执行结果
        int statusCode = response.getStatusLine().getStatusCode();//获取返回的状态值
        if (statusCode != HttpStatus.SC_OK) {
            return null;
        } else {
            String result = EntityUtils.toString(response.getEntity(), "UTF-8");
            return result;
        }
    } catch (Exception e) {
        logger.error("httpget Exception handle-- > " + e);
    } finally {
        if (response != null){
            try {
                response.close();//关闭response
            } catch (IOException e) {
                logger.error("httpget IOException handle-- > " + e);
            }
        }
        if(httpclient != null){
            try {
                httpclient.close();//关闭httpclient
            } catch (IOException e) {
                logger.error("httpget IOException handle-- > " + e);
            }
        }
    }
    return null;
}

2.2 模拟HttpPost请求

/**
 * 模拟HttpPost请求
 * @param url
 * @param jsonString
 * @return
 */
public static String HttpPost(String url, String jsonString){
    CloseableHttpResponse response = null;
    CloseableHttpClient httpClient = HttpClientBuilder.create().build();//创建CloseableHttpClient
    HttpPost httpPost = new HttpPost(url);//实现HttpPost
    RequestConfig requestConfig = RequestConfig.custom().setSocketTimeout(3000).setConnectTimeout(3000).build();
    httpPost.setConfig(requestConfig); //设置httpPost的状态参数
    httpPost.addHeader("Content-Type", "application/json");//设置httpPost的请求头中的MIME类型为json
    StringEntity requestEntity = new StringEntity(jsonString, "utf-8");
    httpPost.setEntity(requestEntity);//设置请求体
    try {
        response = httpClient.execute(httpPost, new BasicHttpContext());//执行请求返回结果
        if (response.getStatusLine().getStatusCode() != HttpStatus.SC_OK) {
            return null;
        }
        HttpEntity entity = response.getEntity();
        if (entity != null) {
            String resultStr = EntityUtils.toString(entity, "utf-8");
            return resultStr;
        } else {
            return null;
        }
    } catch (Exception e) {
        logger.error("httpPost method exception handle-- > " + e);
        return null;
    } finally {
        if (response != null){
            try {
                response.close();//最后关闭response
            } catch (IOException e) {
                logger.error("httpPost method IOException handle -- > " + e);
            }
        }if(httpClient != null){try {httpClient.close();} catch (IOException e) {logger.error("httpPost method exception handle-- > " + e);}
        }
    }
}

不设置参数的简版写法：

    public byte[] get(String url) {
        CloseableHttpResponse response = null;
        try {
            HttpGet httpget = new HttpGet(url);
            response = httpClient.execute(httpget);
            int status = response.getStatusLine().getStatusCode();
            if (status >= 200 && status < 300) {
                ByteArrayOutputStream out = new ByteArrayOutputStream();
                response.getEntity().writeTo(out);
                return out.toByteArray();
            } else {
                throw new ClientProtocolException("Unexpected response status: " + status);
            }
        } catch (IOException e) {
            logger.error("httpClient --> simpleGet IO超时", e);
            throw BusinessException.asBusinessException(BusinessErrorCode.HTTP_IO_EXCEPTION);
        } catch (Exception e) {
            logger.error("httpClient --> simpleGet 未知异常", e);
            throw BusinessException.asBusinessException(BusinessErrorCode.HTTP_UNKNOWN_EXCEPTION);
        } finally {
            if (response != null) {
                try {
                    response.close();
                } catch (IOException var3) {
                    logger.error("closeResponse execute error!!");
                }
            }
        }
    }

public String simplePost(String url, String stringEntity) {
        logger.info("httpClient -> simplePost start, url={},stringEntity={}", url, stringEntity);
        CloseableHttpResponse response = null;
        try {
            HttpPost httpPost = new HttpPost(url);
            StringEntity paramEntity = new StringEntity(stringEntity);
            paramEntity.setContentEncoding("UTF-8");
            paramEntity.setContentType("application/json");
            httpPost.setEntity(paramEntity);
            response = httpClient.execute(httpPost);
            logger.info("httpClient -> simplePost, response={},s={}", response.toString(), JsonUtil.toJSONString(response));
            logger.info("");
            int status = response.getStatusLine().getStatusCode();
            if (status >= 200 && status < 300) {
                HttpEntity httpEntity = response.getEntity();
                return EntityUtils.toString(httpEntity, defaultCharset);//取出应答字符串
            } else {
                throw new ClientProtocolException("Unexpected response status: " + status);
            }
        } catch (IOException e) {
            logger.error("httpClient --> simplePost IO超时", e);
            throw BusinessException.asBusinessException(BusinessErrorCode.HTTP_IO_EXCEPTION);
        } catch (Exception e) {
            logger.error("httpClient --> simplePost 未知异常", e);
            throw BusinessException.asBusinessException(BusinessErrorCode.HTTP_UNKNOWN_EXCEPTION);
        } finally {
            if (response != null) {
                try {
                    response.close();
                } catch (IOException var3) {
                    logger.error("closeResponse execute error!!");
                }
            }
        }
    }

需要注意的是：如果参数 stringEntity 想以对象的形式作为入参，要这样写，使用JSONObject创建对象：

            List<String> testList = new ArrayList();
            testList.add("testString123");
            JSONObject jsonObject = new JSONObject();
            jsonObject.put("testList",testList);
            String stringEntity = jsonObject.toJSONString();

而不能这样写，这样写是一个字符串，不是对象：

            String stringEntity = sonUtil.toJSONString(testList);