转：https://www.cnblogs.com/brokencolor/p/8575440.html

Java的URL类(二)

实例：

Java 通过HttpURLConnection Post方式提交json，并从服务端返回json数据

package Demo.Test;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class App {

    public static void readParse(String urlPath,String str) throws Exception {
        System.out.println(str);

        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        byte[] data = new byte[1024];
        int len = 0;

        URL url = new URL(urlPath);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        // 设置传递方式
        conn.setRequestMethod("POST");
        //代理
        conn.addRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");

        conn.setRequestProperty("Content-Type", "application/json");
        conn.setDoOutput(true);
        conn.setDoInput(true);
        // 设置不用缓存
        conn.setUseCaches(false);
        //权限
        conn.setRequestProperty("Authorization", " Bearer fc58be57c46b32f9a2c32e5393684ac0");

         // 开始连接请求
        conn.connect();
        OutputStream  out = conn.getOutputStream();
        // 写入请求的字符串
        out.write((str).getBytes());
        out.flush();
        out.close();

        // 请求返回的状态
        if (conn.getResponseCode() == 200) {
            System.out.println("连接成功");
            // 请求返回的数据
            InputStream in = conn.getInputStream();
            String a = null;
            try {
                byte[] data1 = new byte[in.available()];
                in.read(data1);
                // 转成字符串
                a = new String(data1);
                System.out.println(a);
            } catch (Exception e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
        } else {
            System.out.println(conn.getResponseCode()+":no++");
        }

    }
    public static void main(String[] args) throws Exception {//地址
        String url = "http://...";
        //查询参数
        String str = "{\"ids\":[15410,15402]}";
        readParse(url,str);
    }
}

注：如果你的代码报错：java.io.IOException: Server returned HTTP response code: 403 for URL https://...... 访问被拒绝

　　你需要在代码中加入请求头信息

// 设置允许输出
conn.setDoOutput(true);

conn.setDoInput(true);

// 设置不用缓存
conn.setUseCaches(false);
// 设置传递方式
conn.setRequestMethod("POST");
// 设置维持长连接
conn.setRequestProperty("Connection", "Keep-Alive");
// 设置文件字符集:
conn.setRequestProperty("Charset", "UTF-8");

// 设置文件长度
conn.setRequestProperty("Content-Length", String.valueOf(data.length));

// 设置文件类型:
conn.setRequestProperty("contentType", "application/json");
//代理
conn.addRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");
//权限---需要根据自己情况进行修改
conn.setRequestProperty("Authorization", " Bearer fc58be57c46b32f9a2c32e5393684ac0");

GET方式访问weatherAPI接口实例

 1 import java.io.InputStream;
 2 import java.net.URL;
 3 import java.net.URLConnection;
 4
 5 public class WeatherAPI {
 6
 7     public static void main(String[] args) throws Exception {
 8         // TODO Auto-generated method stub
 9         WeatherAPI.json("北京");
10         //3秒后继续执行
11         Thread.sleep(3000);
12         WeatherAPI.xml("东京");
13     }
14     public static void json(String strcity) throws Exception{
15         //参数url化
16         String city = java.net.URLEncoder.encode(strcity, "utf-8");
17         //拼地址
18         String apiUrl = String.format("https://www.sojson.com/open/api/weather/json.shtml?city=%s",city);
19         //开始请求
20         URL url= new URL(apiUrl);
21         URLConnection open = url.openConnection();
22         InputStream input = open.getInputStream();
23         //这里转换为String，带上包名，怕你们引错包
24         String result = org.apache.commons.io.IOUtils.toString(input,"utf-8");
25         //输出
26         System.out.println(result);
27     }
28
29     public static void xml(String strcity) throws Exception{
30         //参数url化
31         String city = java.net.URLEncoder.encode(strcity, "utf-8");
32         //拼地址
33         String apiUrl = String.format("https://www.sojson.com/open/api/weather/xml.shtml?city=%s",city);
34         //开始请求
35         URL url= new URL(apiUrl);
36         URLConnection open = url.openConnection();
37         InputStream input = open.getInputStream();
38         //这里转换为String，带上包名，怕你们引错包
39         String result = org.apache.commons.io.IOUtils.toString(input,"utf-8");
40         //输出
41         System.out.println(result);
42     }
43 }

原文地址：https://www.cnblogs.com/wenhuang/p/9891223.html