How does java initiate an http request and call the post and get interfaces?

1. Java calls the post interface

1. Use URLConnection or HttpURLConnection

java comes with it, no need to download other jar packages

Called in URLConnection mode, if the interface response code is modified by the server, the return message cannot be received. The return message can only be received when the response code is correct

public static String sendPost(String url, String param) {
        OutputStreamWriter out = null;
        BufferedReader in = null;
        StringBuilder result = new StringBuilder("");
        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("Content-Type","application/json;charset=UTF-8");
            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
            out = new OutputStreamWriter(conn.getOutputStream(), "UTF-8");
            // 发送请求参数
            out.write(param);
            // flush输出流的缓冲
            out.flush();
            // 定义BufferedReader输入流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(conn.getInputStream(),"UTF-8"));
            String line;
            while ((line = in.readLine()) != null) {
                result.append(line);
            }
        } catch (Exception e) {
            System.out.println("发送 POST 请求出现异常！"+e);
            e.printStackTrace();
        }
        //使用finally块来关闭输出流、输入流
        finally{
        	if(out!=null){ try { out.close(); }catch(Exception ex){} }
        	if(in!=null){ try { in.close(); }catch(Exception ex){} }
        }
        return result.toString();
    }

HttpURLConnection method called

//ms超时毫秒,url地址,json入参
public static String httpJson(int ms,String url,String json) throws Exception{
		String err = "00", line = null;
		StringBuilder sb = new StringBuilder();
		HttpURLConnection conn = null;
		BufferedWriter out = null;
		BufferedReader in = null;
		try{
			conn = (HttpURLConnection) (new URL(url.replaceAll("／","/"))).openConnection();
			conn.setRequestMethod("POST");
			conn.setDoOutput(true);
			conn.setDoInput(true);
			conn.setUseCaches(false);
			conn.setConnectTimeout(ms);
			conn.setReadTimeout(ms);
			conn.setRequestProperty("Content-Type","application/json;charset=utf-8");
			conn.connect();
			out = new BufferedWriter(new OutputStreamWriter(conn.getOutputStream(),"utf-8"));
			out.write(new String(json.getBytes(), "utf-8"));
			out.flush();//发送参数
			int code = conn.getResponseCode();
			if (conn.getResponseCode()==200){
				in = new BufferedReader(new InputStreamReader(conn.getInputStream(),"UTF-8"));
				while ((line=in.readLine())!=null)
					sb.append(line);
			}//接收返回值
			
		}catch(Exception ex){
			err=ex.getMessage();
		}
		try{ if (out!=null) out.close(); }catch(Exception ex){}; 
		try{ if (in!=null) in.close(); }catch(Exception ex){};
		try{ if (conn!=null) conn.disconnect();}catch(Exception ex){}
		if (!err.equals("00")) throw new Exception(err);
		return sb.toString();
	}

2. Use the jar package used by CloseableHttpClient

<dependency>
    <groupId>com.alibaba.csb.sdk</groupId>
    <artifactId>http-client</artifactId>
    <version>1.1.5.1</version>
</dependency>

public static String httpPostJson(String url,String json) throws Exception{
		String data=""; 
		CloseableHttpClient httpClient = null;
		CloseableHttpResponse response = null;
		try {
			httpClient = HttpClients.createDefault();
			HttpPost httppost = new HttpPost(url);
			httppost.setHeader("Content-Type", "application/json;charset=UTF-8");
			StringEntity se = new StringEntity(json,Charset.forName("UTF-8"));
	        se.setContentType("text/json");
	        se.setContentEncoding("UTF-8");
	        httppost.setEntity(se);
	        response = httpClient.execute(httppost);
	        int code = response.getStatusLine().getStatusCode();
	        System.out.println("接口响应码:"+code);
	        data = EntityUtils.toString(response.getEntity(), "utf-8");
	        EntityUtils.consume(response.getEntity());
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			if(response!=null){ try{response.close();}catch (IOException e){} }
			if(httpClient!=null){ try{httpClient.close();}catch(IOException e){} }
		}
		return data;
	}

3. Use the jar package used by HttpCaller

is the same as the jar package in the second one.

public static String sendPost(){
		String result = "";
		HttpParameters.Builder builder = HttpParameters.newBuilder();
		builder.requestURL("URL") // 设置请求的URL
        		.api("api") // 设置服务名
        		.version("version") // 设置版本号
        		.method("post") // 设置调用方式, get/post
        		.accessKey("ak").secretKey("sk"); // 设置accessKey 和 设置secretKey
		// 设置请求参数（json格式)
        Map<String,String> param = new HashMap<String,String>();
        param.put("key1","value1");
        param.put("key2","value2");
        //加密，没有加密则不需要encryptParam，直接用param
        Map<String,String> encryptParam = new HashMap<String,String>();
        encryptParam.put("key3", getData(JSON.toJSONString(param)));
        ContentBody cb = new ContentBody(JSON.toJSONString(encryptParam));
        builder.contentBody(cb);
        
        try {
        	result = HttpCaller.invoke(builder.build());
		} catch (Exception e) {
			e.printStackTrace();
		}
		
        return result;
	}
	
	//自己的加密方式
	public static String getData(String data1){
		return "加密后的密文";
	}

2. Java calls the get interface

Use the URLConnection that comes with java

//将map型转为请求参数型
public static String getUrlData(Map<Object, Object> data) throws Exception{
	StringBuffer sb = new StringBuffer();
	try {
		Set<Map.Entry<Object, Object>> entries = data.entrySet();
		Iterator<Map.Entry<Object, Object>> iterators = entries.iterator();
		while(iterators.hasNext()){
			Map.Entry<Object, Object> next = iterators.next();
			sb.append(next.getKey().toString().trim()).append("=").append(URLEncoder.encode(next.getValue() + "", "UTF-8").trim()).append("&");
		}
		sb.deleteCharAt(sb.length() - 1);
	} catch (Exception e) {
		sb.append(e.toString());
	}
	return sb.toString();
}

//strUrl截止到?，例：http://127.0.0.1:8080/api/method?
public static String httpGet(String strUrl){
	Map<Object, Object> params = new HashMap<Object, Object>();
	params.put("key1", "value1");
	params.put("key2", "value2");
	String url=strUrl + getUrlData(params);
	
  	StringBuilder result = new StringBuilder();
    BufferedReader in = null;
    try {
        URL realUrl = new URL(url);
        // 打开和URL之间的连接
        URLConnection connection = realUrl.openConnection();
        // 设置通用的请求属性
        connection.setRequestProperty("accept", "*/*");
        connection.setRequestProperty("connection", "Keep-Alive");
        connection.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
        // 建立实际的连接
        connection.connect();
        // 获取所有响应头字段
        // 定义 BufferedReader输入流来读取URL的响应
        in = new BufferedReader(new InputStreamReader(connection.getInputStream(),"UTF-8"));
        String line;
        while ((line = in.readLine()) != null) {
            result.append(line);
        }
    } catch (Exception e) {
        System.out.println("发送GET请求出现异常！" + e);
        e.printStackTrace();
    }
    finally {
    	if (in != null){ try { in.close(); }catch(Exception e2){} }
    }
    return result.toString();
}

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