Java获取http和https协议返回的json数据

获取HTTP/HTTPS协议返回的JSON数据可以通过Java提供的HttpClient库来实现。以下是完整的攻略：

准备工作

在使用HttpClient库之前，需要先引入该库。可以在Maven项目中添加以下依赖：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.12</version>
</dependency>

发送HTTP GET请求获取JSON数据

下面是一个示例代码，使用HttpGet方法发送HTTP GET请求获取JSON数据：

import java.io.IOException;
import java.util.Scanner;
import org.apache.http.HttpEntity;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

public class HttpJsonGetDemo {
  public static void main(String[] args) throws IOException {
    HttpClient httpClient = HttpClients.createDefault();
    HttpGet request = new HttpGet("https://jsonplaceholder.typicode.com/todos/1");

    HttpEntity responseEntity = httpClient.execute(request).getEntity();
    String responseString = EntityUtils.toString(responseEntity);

    ObjectMapper mapper = new ObjectMapper();
    JsonNode node = mapper.readTree(responseString);
    int id = node.get("id").asInt();
    String title = node.get("title").asText();
    boolean completed = node.get("completed").asBoolean();

    System.out.println("id: " + id);
    System.out.println("title: " + title);
    System.out.println("completed: " + completed);
  }
}

在这个示例中，我们使用了 HttpClient 发送了一个 HttpGet 请求，并获取返回数据后将其解析成一个 JsonNode 对象。

发送HTTPS GET请求获取JSON数据

如果需要访问HTTPS站点，需要对 HttpClient 进行配置。以下示例展示如何配置并发送HTTP GET请求：

import java.io.IOException;
import org.apache.http.HttpEntity;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.ssl.SSLContexts;
import org.apache.http.ssl.TrustStrategy;
import org.apache.http.util.EntityUtils;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

public class HttpsJsonGetDemo {
  public static void main(String[] args) throws Exception {
    HttpClient httpClient = HttpClients.custom()
        .setSSLContext(SSLContexts.custom().loadTrustMaterial(null, new TrustStrategy() {
          @Override
          public boolean isTrusted(java.security.cert.X509Certificate[] chain, String authType)
              throws java.security.cert.CertificateException {
            return true;
          }
        }).build())
        .build();

    HttpGet request = new HttpGet("https://jsonplaceholder.typicode.com/todos/1");

    HttpEntity responseEntity = httpClient.execute(request).getEntity();
    String responseString = EntityUtils.toString(responseEntity);

    ObjectMapper mapper = new ObjectMapper();
    JsonNode node = mapper.readTree(responseString);
    int id = node.get("id").asInt();
    String title = node.get("title").asText();
    boolean completed = node.get("completed").asBoolean();

    System.out.println("id: " + id);
    System.out.println("title: " + title);
    System.out.println("completed: " + completed);
  }
}

在这个示例中，我们使用自定义的 HttpClient，将其SSL使用的证书设置为信任所有证书，从而允许访问HTTPS站点。通过以上示例代码，可以方便地使用Java获取http和https协议返回的JSON数据。