Java中发送Http请求之httpClient

HTTP 协议是 Internet 上使用得最多、最重要的协议之一，越来越多的 Java 应用程序需要直接通过 HTTP 协议来访问网络资源, JDK 的 java net包中已经提供了访问 HTTP 协议的基本功能，但是对于大部分应用程序来说，JDK 库本身提供的功能还不够丰富和灵活.

1 httpClient的简介

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.

其主要特性:

• 实现了所有 HTTP 的方法（GET,POST,PUT,DELETE,HEAD 等)
• 支持自动转向
• 支持 HTTPS 协议
• 支持代理服务器(Nginx等)

使用步骤:

1 创建HttpClient对象

2 创建请求方法对象, 如发送GET请求, 则创建HttpGet对象; 如发送POST请求,则创建HttpPost对象

3 添加请求参数,可通过setParams方法添加普通请求参数, 对于POST请求,请求体参数,采用setEntity方法添加请求体参数

4 使用HttpClient对象的execute方法发送请求,返回HttpResponse响应对象

5 响应对象HttpResponse的方法, 可以获取服务器的响应头,响应体等信息

2 httpClient的案列

@Slf4j
public class HttpClientDemo {
    
    
    // 使用HttpClients工具类生成
    // HttpClient  httpClient = HttpClients.createDefault();

    /**
     * 无参GET请求
     */
    public static String doGetTestByNotParam() {
    
    
        String url = "http://localhost:8889/consumer/get";

        // 1 获取httpClient客户端
       HttpClient httpClient = HttpClients.createDefault();
        
        HttpClient httpClient = HttpClientBuilder.create().build();
        // 2 创建请求
        HttpGet httpGet = new HttpGet(url);

        // 3 发送请求
        HttpResponse httpResponse = null;
        try {
    
    
            httpResponse = httpClient.execute(httpGet);

            // 4 响应状态码 响应信息
            int statusCode = httpResponse.getStatusLine().getStatusCode();
            log.info("响应状态码为: {} ", statusCode);

            // 响应信息
            HttpEntity httpEntity = httpResponse.getEntity();
            log.info("响应内容为: {} ", EntityUtils.toString(httpEntity));

            //释放资源
            EntityUtils.consume(httpEntity);
            return EntityUtils.toString(httpEntity);
        } catch (IOException e) {
    
    
            log.info("请求异常, 错误信息为: {} ", e.getMessage());
            return null;
        }

    }

    /**
     * 有参GET请求 添加请求配置
     */
    public static String doGetTestByParam() {
    
    
        String url = "http://localhost:8889/consumer/get";

        String param = "key=1234545&id=123123123";

        //  获取httpClient客户端
        HttpClient httpClient = HttpClientBuilder.create().build();
        //  创建GET请求
        HttpGet httpGet = new HttpGet(url + "?" + param);

        // 配置请求信息
        RequestConfig requestConfig = RequestConfig.custom()
                .setConnectTimeout(5000) // 连接超时时间
                .setConnectionRequestTimeout(5000) //请求超时时间
                .setSocketTimeout(5000) // 读写超时时间
                .setRedirectsEnabled(true) // 是否重定向 默认true开启
                .build();
        httpGet.setConfig(requestConfig);

        //  发送请求
        HttpResponse httpResponse = null;
        try {
    
    
            httpResponse = httpClient.execute(httpGet);

            // 4 响应状态码 响应信息
            int statusCode = httpResponse.getStatusLine().getStatusCode();
            log.info("响应状态码为: {} ", statusCode);

            // 响应信息
            HttpEntity httpEntity = httpResponse.getEntity();
            log.info("响应内容为: {} ", EntityUtils.toString(httpEntity));

            //释放资源
            EntityUtils.consume(httpEntity);
            return EntityUtils.toString(httpEntity);
        } catch (IOException e) {
    
    
            log.info("请求异常, 错误信息为: {} ", e.getMessage());
            return null;
        }

    }

    /**
     * 有参GET请求 添加请求配置
     */
    public static String doGetTestByURI() {
    
    
        String url = "http://localhost:8889/consumer/get";

        String param = "key=1234545&id=123123123";

        //  获取httpClient客户端
        HttpClient httpClient = HttpClientBuilder.create().build();

        List<NameValuePair> params = new ArrayList<>();
        params.add(new BasicNameValuePair("key", "123456"));
        params.add(new BasicNameValuePair("id", "123123"));

        //  发送请求
        HttpResponse httpResponse = null;
        URI uri = null;
        try {
    
    

            uri = new URIBuilder()
                    .setScheme("http")
                    .setHost("localhost")
                    .setPort(8898)
                    .setPath("/test")
                    .setParameters(params)
                    .build();
            //  创建GET请求
            HttpGet httpGet = new HttpGet(uri);

            httpResponse = httpClient.execute(httpGet);

            // 配置请求信息
            RequestConfig requestConfig = RequestConfig.custom()
                    .setConnectTimeout(5000) // 连接超时时间
                    .setConnectionRequestTimeout(5000) //请求超时时间
                    .setSocketTimeout(5000) // 读写超时时间
                    .setRedirectsEnabled(true) // 是否重定向 默认true开启
                    .build();
            httpGet.setConfig(requestConfig);

            // 4 响应状态码 响应信息
            int statusCode = httpResponse.getStatusLine().getStatusCode();
            log.info("响应状态码为: {} ", statusCode);

            // 响应信息
            HttpEntity httpEntity = httpResponse.getEntity();
            log.info("响应内容为: {} ", EntityUtils.toString(httpEntity));

            //释放资源
            EntityUtils.consume(httpEntity);
            return EntityUtils.toString(httpEntity);
        } catch (Exception e) {
    
    
            log.info("请求异常, 错误信息为: {} ", e.getMessage());
            return null;
        }

    }

    /**
     * 无参POST请求
     */
    public static String doPostTestByNotParam() {
    
    
        // 请求地址
        String url = "http://localhost:8889/consumer/post";

        //  获取httpClient客户端
        HttpClient httpClient = HttpClientBuilder.create().build();
        //  创建请求
        HttpPost httpPost = new HttpPost(url);

        //  发送请求
        HttpResponse httpResponse = null;
        try {
    
    
            httpResponse = httpClient.execute(httpPost);

            //  响应状态码 响应信息
            int statusCode = httpResponse.getStatusLine().getStatusCode();
            log.info("响应状态码为: {} ", statusCode);

            // 响应信息
            HttpEntity httpEntity = httpResponse.getEntity();
            log.info("响应内容为: {} ", EntityUtils.toString(httpEntity));

            //释放资源
            EntityUtils.consume(httpEntity);
            return EntityUtils.toString(httpEntity);
        } catch (IOException e) {
    
    
            log.info("请求异常, 错误信息为: {} ", e.getMessage());
            return null;
        }

    }

    /**
     * 有参POST请求
     */
    public static String doPostTestByParam() {
    
    

        // 请求地址
        String url = "http://localhost:8889/consumer/post";

        // post请求
        HttpClient httpClient = null;
        HttpPost postMethod = null;
        HttpResponse response = null;
        String responseContent = null;

        try {
    
    
            // 获取http客户端
            httpClient = HttpClients.createDefault();
            postMethod = new HttpPost(url);

            // 自定义对象
            User user = new User();

            // 设置请求头
            postMethod.addHeader("Content-Type", "application/json;charset=utf8");
            // 封装请求体
            postMethod
                    .setEntity(new StringEntity(JSON.toJSONString(user), Charset.forName("UTF-8")));

            // 发送请求
            response = httpClient.execute(postMethod);

            // 获取响应结果
            int statusCode = response.getStatusLine().getStatusCode();

            // 响应对象
            HttpEntity httpEntity = response.getEntity();

            // 响应的字符串
            responseContent = EntityUtils.toString(httpEntity, "UTF-8");

            //释放资源
            EntityUtils.consume(httpEntity);
            return responseContent;
        } catch (IOException e) {
    
    
            log.info("请求异常, 错误信息为: {} ", e.getMessage());
            return null;
        }

    }

}

HttpClients对象

HttpClients的createDefault()方法,也是调用了HttpClientBuilder.create().build();构造器模式创建了一个CloseableHttpClient对象.

public class HttpClients {
    
    
    private HttpClients() {
    
    
    }

    public static HttpClientBuilder custom() {
    
    
        return HttpClientBuilder.create();
    }

    public static CloseableHttpClient createDefault() {
    
    
        return HttpClientBuilder.create().build();
    }

    public static CloseableHttpClient createSystem() {
    
    
        return HttpClientBuilder.create().useSystemProperties().build();
    }

    public static CloseableHttpClient createMinimal() {
    
    
        return new MinimalHttpClient(new PoolingHttpClientConnectionManager());
    }

    public static CloseableHttpClient createMinimal(HttpClientConnectionManager connManager) {
    
    
        return new MinimalHttpClient(connManager);
    }
}

CloseableHttpClient对象

它是HttpClient接口的唯一抽象类.发送请求时,调用execute方法,

public abstract class CloseableHttpClient implements HttpClient, Closeable {
    
    
    private final Log log = LogFactory.getLog(this.getClass());

    public CloseableHttpClient() {
    
    
    }

    public CloseableHttpResponse execute(HttpUriRequest request) throws IOException, ClientProtocolException {
    
    
        return this.execute(request, (HttpContext)null);
    }
    
    public CloseableHttpResponse execute(HttpUriRequest request, HttpContext context) throws IOException, ClientProtocolException {
    
    
        Args.notNull(request, "HTTP request");
        return this.doExecute(determineTarget(request), request, context);
    }
    
    protected abstract CloseableHttpResponse doExecute(HttpHost var1, HttpRequest var2, HttpContext var3) throws IOException, ClientProtocolException;


}

HttpGet对象

继承自HttpRequestBase对象,HttpGet请求对象,用来发送GET请求. 查阅代码,发现其构造方法有如下三种.

public class HttpGet extends HttpRequestBase {
    
    
    public static final String METHOD_NAME = "GET";

    public HttpGet() {
    
    
    }

    public HttpGet(URI uri) {
    
    
        this.setURI(uri);
    }

    public HttpGet(String uri) {
    
    
        this.setURI(URI.create(uri));
    }

    public String getMethod() {
    
    
        return "GET";
    }
}

HttpPost对象

继承自HttpEntityEnclosingRequestBase对象,HttpPost请求对象,用来发送POST请求. 查阅代码,发现其构造方法有如下三种.

public class HttpPost extends HttpEntityEnclosingRequestBase {
    
    
    public static final String METHOD_NAME = "POST";

    public HttpPost() {
    
    
    }

    public HttpPost(URI uri) {
    
    
        this.setURI(uri);
    }

    public HttpPost(String uri) {
    
    
        this.setURI(URI.create(uri));
    }

    public String getMethod() {
    
    
        return "POST";
    }
}

HttpResponse对象

请求响应对象, 主要使用的是其实现类BasicHttpResponse.

public interface HttpResponse extends HttpMessage {
    
    
    StatusLine getStatusLine();

    void setStatusLine(StatusLine var1);

    void setStatusLine(ProtocolVersion var1, int var2);

    void setStatusLine(ProtocolVersion var1, int var2, String var3);

    void setStatusCode(int var1) throws IllegalStateException;

    void setReasonPhrase(String var1) throws IllegalStateException;

    HttpEntity getEntity();

    void setEntity(HttpEntity var1);

    Locale getLocale();

    void setLocale(Locale var1);
}

BasicHttpResponse对象

其中常用的属性有StatusLine响应状态码,HttpEntity响应信息对象等.

public class BasicHttpResponse extends AbstractHttpMessage implements HttpResponse {
    
    
    // 状态码
    private StatusLine statusline;
    private ProtocolVersion ver;
    private int code;
    private String reasonPhrase;
    // 响应信息对象
    private HttpEntity entity;
    private final ReasonPhraseCatalog reasonCatalog;
    private Locale locale;
    // ...
}