springboot调用第三方接口

1. 了解：
   在发送请求头时：
   （1）Content-Type: 发送端（客户端、服务端）发送的实体数据类型
   （2）Accept : 客户端想要接收的数据类型
   （3）Content-Type:application/x-www-form-urlencoded：指的是key=value&key=value ，get和post方式都是这个类型，只是get多了个？，post方式把参数放在请求体内
   （4）Accept中经常能看到 image/gif 等等 ，其中 / ，表示接受所有类型
   （5）请求头中存在 Connect：Keep-Alive 实际上它是一种TCP复用，每次http请求都需要tcp三次握手，浪费资源和时间，因此我们可以保持tcp通道连接一段时间，这样一次tcp连接就可以维持几次http请求。
   （6）请求头中的User-Agent： 大体指支持的浏览器，所有浏览器都想伪装成mozilla，避免代码被阉割，部分功能无法实现
   （7）具体参考：http请求参数详情
2. 使用spring3.0提供的HTTP 请求工具RestTemplate进行接口的调用：

package xiamen.yyr.interfacecall.util;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import org.springframework.http.*;
import org.springframework.util.MultiValueMap;
import org.springframework.web.client.RestTemplate;

import java.util.HashMap;
import java.util.Map;

/** * @Description: 调用接口 * @Author： * @Date：2021/5/13 */
public class HttpUtil { 
    public static final String HTTPGETMETHOD = "GET";
    public static final String HTTPPOSTMETHOD = "POST";

    /*****************************x-www-form-urlencoded*******************************/

    //MultiValueMap HttpEntity中的参数就是这个，表示一个键对应多个值，value是一个list集合
    public static <T> T postRequestByUrlencoded(String url , MultiValueMap<String , String> params , Class<T> clazz) { 
        RestTemplate restTemplate = new RestTemplate();
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
        HttpEntity<MultiValueMap<String, String>> httpEntity = new HttpEntity<>(params, headers);
        ResponseEntity<String> response = restTemplate.exchange(url , HttpMethod.POST , httpEntity , String.class);
        if (response!=null && response.getStatusCode()==HttpStatus.OK){ 
            String body = response.getBody();
            if (body != null){ 
                Gson gson = new GsonBuilder().create();
                return gson.fromJson(body , clazz);
            }
            return  null;
        }
        return null;
    }


    public static <T> T getRequestByUrlencoded(String url , HashMap<String , Object> params , Class<T> clazz){ 
        RestTemplate restTemplate = new RestTemplate();

        //params 请求参数拼接
        if (params!=null && params.size()>0){ 
                StringBuilder urlbuilder = new StringBuilder(url);
            urlbuilder.append("?");
            for (Map.Entry<String , Object> param : params.entrySet()){ 
                urlbuilder.append(param.getKey()).append("=").append(param.getValue()).append("&");
            }
            url = urlbuilder.substring(0 , urlbuilder.length() - 1);
        }

        String result = restTemplate.getForObject(url , String.class);

        if (result != null){ 
            Gson gson = new GsonBuilder().create();
            return gson.fromJson(result , clazz);
        }
        return null;
    }


    /*****************************json*******************************/

    public static <T> T postRequestByJson(String url , String jsonObject , Class<T> clazz) { 
        RestTemplate restTemplate = new RestTemplate();
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        HttpEntity<Object> httpEntity = new HttpEntity<>(jsonObject, headers);
        ResponseEntity<String> response = restTemplate.exchange(url , HttpMethod.POST , httpEntity , String.class);
        if (response!=null && response.getStatusCode()==HttpStatus.OK){ 
            String body = response.getBody();
            if (body != null){ 
                Gson gson = new GsonBuilder().create();
                return gson.fromJson(body , clazz);
            }
            return  null;
        }
        return null;
    }
}

3.使用java.net自带的HttpURLConnection进行第三方接口的调用：

package xiamen.yyr.interfacecall.util;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import org.apache.logging.log4j.util.Strings;
import org.springframework.util.CollectionUtils;
import org.springframework.util.StringUtils;

import java.io.*;
import java.lang.reflect.Type;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

/** * @Description: * @Author： * @Date：2021/5/17 */
public class HttpUtil2 { 

    /****************************************x-www-form-urlencoded*********************************************/
    public static <T> T getRequestByUrlencoded(String path , HashMap<String , Object> params, Type clazz){ 
        HttpURLConnection conn = null;
        BufferedReader br = null;
        InputStream is = null;
        String body = "";
        StringBuffer sb = new StringBuffer(path);
        //请求参数拼接到路径上
        if (!CollectionUtils.isEmpty(params)){ 
            sb.append("?");
            for (Map.Entry<String , Object> entry : params.entrySet()){ 
                sb.append(entry.getKey()).append("=").append(entry.getValue()).append("&");
            }
            body = sb.substring(0 , sb.length()-1);
        }
        try { 
            URL url = new URL(body);
            //打开与url之间的连接
            conn = (HttpURLConnection) url.openConnection();
            //不设置默认使用get
            conn.setRequestMethod("GET");
            conn.setRequestProperty("accept" , "*/*");
            conn.setRequestProperty("user-agent" , "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
            conn.setRequestProperty("content-Type" , "application/x-www-form-urlencoded");
            conn.setRequestProperty("connection" , "keep-Alive");

            //本次连接是否自动使用重定向
            conn.setInstanceFollowRedirects(true);
            is = conn.getInputStream();
            br = new BufferedReader(new InputStreamReader(is));
            StringBuffer result = new StringBuffer();
            while ((body=br.readLine()) != null){ 
                result.append(body);
            }
            body = result.toString();
            if (Strings.isNotBlank(body)){ 
                Gson gson = new GsonBuilder().create();
                return gson.fromJson(body , clazz);
            }
        } catch (MalformedURLException e) { 
            e.printStackTrace();
        } catch (IOException e) { 
            e.printStackTrace();
        }finally { 
            if (br != null){ 
                try { 
                    br.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }

            if (is != null){ 
                try { 
                    is.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }

            if (conn != null){ 
                conn.disconnect();
            }
        }
        return null;
    }


    public static <T> T postRequestByUrlencoded(String path , HashMap<String , String> headers , Type clazz){ 
        DataOutputStream out = null;
        BufferedReader br = null;
        InputStream is = null;
        HttpURLConnection conn = null;
        StringBuffer sb = new StringBuffer();
        StringBuffer result = new StringBuffer();
        String body = "";
        try { 
            URL url = new URL(path);
            //打开与url之间的连接
            conn = (HttpURLConnection) url.openConnection();
            //设置请求方式
            conn.setRequestMethod("POST");
            // Post 请求不能使用缓存
            conn.setUseCaches(false);
            //设置本次连接是否自动重定向
            conn.setInstanceFollowRedirects(true);
            //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)");
            conn.setRequestProperty("content-Type" , "application/x-www-form-urlencoded");

            if (!CollectionUtils.isEmpty(headers)){ 
                for (Map.Entry<String , String> entry : headers.entrySet()){ 
                    sb.append(entry.getKey()).append("=").append(entry.getValue()).append("&");
                }
                body =  sb.substring(0 , sb.length()-1);
            }

            //setDoOutput设置是否向httpUrlConnection输出，setDoInput设置是否向httpUrlConnection读入，发送post请求必须设置这两个属性
            conn.setDoOutput(true);
            conn.setDoInput(true);

            //获取URLConnection对象对应的输出流
            out = new DataOutputStream(conn.getOutputStream());
            //发送请求参数即数据
            out.writeBytes(body);
            out.flush();
            //获取URLConnection对象对应的输入流
            is = conn.getInputStream();
            br = new BufferedReader(new InputStreamReader(is));
            String str = "";
            while ((str=br.readLine())!=null){ 
                result.append(str);
            }
            str = result.toString();
            if (Strings.isNotBlank(str)){ 
                Gson gson = new GsonBuilder().create();
                return gson.fromJson(str , clazz);
            }

        } catch (MalformedURLException e) { 
            e.printStackTrace();
        } catch (IOException e) { 
            e.printStackTrace();
        }finally { 
            if(is != null){ 
                try { 
                    is.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (br != null){ 
                try { 
                    br.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (out != null){ 
                try { 
                    out.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (conn != null){ 
                conn.disconnect();
            }
        }
        return null;
    }

/*************************************application/json*************************************************/
   //此方法可以使用，但具体是否正确有待商榷
   //首先：get请求方式传递json数据应该放在请求协议包的哪里，其次：setDoOutput方法要设置为true，即使是get方式，否则无法向URLConnection发送数据
    public static <T> T getRequestByJson(String path , String data ,Type clazz){ 
        OutputStreamWriter out = null;
        BufferedReader br = null;
        InputStream is = null;
        HttpURLConnection conn = null;
        StringBuffer sb = new StringBuffer();
        String result = "";

        try { 
            URL url = new URL(path);
            conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");

            conn.setRequestProperty("accept" , "*/*");
            conn.setRequestProperty("connection" , "keep-Alive");
            conn.setRequestProperty("user-agent" , "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
            conn.setRequestProperty("content-Type" , "application/json;charset=utf-8");
            
            //从源码看，应该是检查是否连接，未连接的话进行连接
            conn.setDoOutput(true);
            conn.setDoInput(true);

            out = new OutputStreamWriter(conn.getOutputStream() , "UTF-8");
            out.write(data);
            out.flush();

            is = conn.getInputStream();
            br = new BufferedReader(new InputStreamReader(is));
            String body = "";
            while ((body=br.readLine())!=null){ 
                sb.append(body);
            }
            result = sb.toString();
            if (Strings.isNotBlank(result)){ 
                Gson gson = new GsonBuilder().create();
                return gson.fromJson(result , clazz);
            }
        } catch (MalformedURLException e) { 
            e.printStackTrace();
        } catch (IOException e) { 
            e.printStackTrace();
        }finally { 
            if(is != null){ 
                try { 
                    is.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (br != null){ 
                try { 
                    br.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (out != null){ 
                try { 
                    out.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (conn != null){ 
                conn.disconnect();
            }
        }
        return null;
    }



    public static <T> T postRequestByJson(String path , String data , Type clazz){ 
        OutputStreamWriter out = null;
        BufferedReader br = null;
        InputStream is = null;
        HttpURLConnection conn = null;
        StringBuffer sb = new StringBuffer();
        String result = "";
        try { 
            URL url = new URL(path);
            //打开与url之间的连接
            conn = (HttpURLConnection) url.openConnection();
            //设置请求方式
            conn.setRequestMethod("POST");
            //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)");
            conn.setRequestProperty("content-Type" , "application/json;charset=utf-8");

            //setDoOutput设置是否向httpUrlConnection输出，setDoInput设置是否向httpUrlConnection读入，发送post请求必须设置这两个属性
            conn.setDoOutput(true);
            conn.setDoInput(true);

            //获取URLConnection对象对应的输出流
            out = new OutputStreamWriter(conn.getOutputStream() , "UTF-8");
            //发送请求参数即数据
            out.write(data);
            out.flush();

            //获取URLConnection对象对应的输入流
            is = conn.getInputStream();
            br = new BufferedReader(new InputStreamReader(is));
            String str = "";
            while ((str=br.readLine())!=null){ 
                sb.append(str);
            }
            str = sb.toString();
            if (Strings.isNotBlank(str)){ 
               Gson gson = new GsonBuilder().create();
               return gson.fromJson(sb.toString() , clazz);
            }

        } catch (MalformedURLException e) { 
            e.printStackTrace();
        } catch (IOException e) { 
            e.printStackTrace();
        }finally { 
            if(is != null){ 
                try { 
                    is.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (br != null){ 
                try { 
                    br.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (out != null){ 
                try { 
                    out.close();
                } catch (IOException e) { 
                    e.printStackTrace();
                }
            }
            if (conn != null){ 
                conn.disconnect();
            }
        }
        return null;
    }
}

1. java11使用了HttpClient调用第三方接口：相比HttpURLConnection，其方法更简便，并且支持发送异步请求（具体参考疯狂java讲义P836）