【Java】发起一个HTTP请求 GET/POST 调用网络API接口

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package httprequest;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.URL;
import java.net.URLConnection;
import java.util.List;
import java.util.Map;
/**
* java发送http的get和post请求
*/
public class HttpRequest {
/**
* 向指定URL发送GET方式的请求
* @param url 发送请求的URL
* @param param 请求参数 
* @return URL 代表远程资源的响应
*/
public static String sendGet(String url){
String result = "";
String urlName = url;
try{
URL realUrl = new URL(urlName);
//打开和URL之间的连接
URLConnection conn = realUrl.openConnection();
//设置通用的请求属性
conn.setRequestProperty("accept", "*/*");
conn.setRequestProperty("connection", "Keep-Alive");
conn.setRequestProperty("user-agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
//建立实际的连接
conn.connect();
//获取所有的响应头字段
Map<String,List<String>> map = conn.getHeaderFields();
//遍历所有的响应头字段
for (String key : map.keySet()) {
System.out.println(key + "-->" + map.get(key));
}
// 定义 BufferedReader输入流来读取URL的响应
BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
result += line;
}
} catch (Exception e) {
System.out.println("发送GET请求出现异常" + e);
e.printStackTrace();
}
return result;
}

/**
* 向指定URL发送POST方式的请求
* @param url 发送请求的URL
* @param param 请求参数 
* @return URL 代表远程资源的响应
*/
public static String sendPost(String url, String param){
String result = "";
try{
URL realUrl = new URL(url);
//打开和URL之间的连接
URLConnection conn = realUrl.openConnection();
//设置通用的请求属性
conn.setRequestProperty("accept", "*/*");
conn.setRequestProperty("connection", "Keep-Alive");
conn.setRequestProperty("user-agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
//发送POST请求必须设置如下两行
conn.setDoOutput(true);
conn.setDoInput(true);
//获取URLConnection对象对应的输出流
PrintWriter out = new PrintWriter(conn.getOutputStream());
//发送请求参数
out.print(param);
//flush输出流的缓冲
out.flush();
// 定义 BufferedReader输入流来读取URL的响应
BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream(), "utf-8"));
String line;
while ((line = in.readLine()) != null) {
result += "\n" + line;
}
} catch (Exception e) {
System.out.println("发送POST请求出现异常" + e);
e.printStackTrace();
}
return result;
}

//测试发送GET和POST请求
public static void main(String[] args) {
//发送GET请求
String s = HttpRequest.sendGet("https://b.julym.com/time.php");
System.out.println(s);
//发送POST请求
String s1 = HttpRequest.sendPost("https://b.julym.com/time.php", "canshu=null");
System.out.println(s1);
}
}