Java 有多种方式可以发送 http 请求，这些方法主要分为两类，第一类是通过 Java 原生类HttpURLConnection发送请求，该方式使用起来相对繁琐一些，但底层逻辑清晰，有利于开发人员了解底层逻辑；第二类是通过第三方 Apache 旗下的专门用来发送 http 请求的 HttpClient 类，该类是对原生的HttpURLConnection类的扩展，功能强大，使用简单。
一、基于HttpURLConnection的请求发送
基于jdk1.7 HttpURLConnection 编写的发送http请求的函数，代码测试可用。顺便介绍了请求头部相关参数的细节，对于读者理解http协议具有一定的帮助，代码如下：
import com.alibaba.fastjson.JSONObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.lang.Nullable;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;
/**
* http请求工具类
*/
public class HttpUtil {
private static final Logger log = LoggerFactory.getLogger(HttpUtil.class);
/**
* http get 请求
* @param url 链接
* @return 请求返回内容
*/
public static String doGet(String url) {
HttpURLConnection connection = null;
InputStream inputStream = null;
BufferedReader reader = null;
StringBuilder response = new StringBuilder();
try {
connection = (HttpURLConnection) new URL(url).openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(15000);
connection.setReadTimeout(15000);
/// 设置请求头部
connection.setRequestProperty("appKey", "123456");
/// The "Accept: */*" header is added to tell the server that the client can understand and process all forms of response content types.
/// 对于SringBoot架构后端使用@RestController注解的类，会返回json格式的数据, 相当于connection.setRequestProperty("Accept", "application/json");
/// 当客户端未设置Accept头部时，默认值为"text/html;"，此时服务端返回内容为html格式；
connection.setRequestProperty("Accept", "*/*");
/// 发起连接请求
connection.connect();
/// 读取返回数据
inputStream = connection.getResponseCode() == 200 ? connection.getInputStream() : connection.getErrorStream();
if(inputStream != null) {
reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
String line;
while ((line = reader.readLine()) != null) {
response.append(line);
}
}
} catch (IOException e) {
log.error(e.getMessage(), e);
} finally {
if(reader != null){
try {
reader.close();
} catch (IOException e) {
log.error(e.getMessage(), e);
}
}
if(inputStream != null) {
try {
inputStream.close();
} catch (IOException e) {
log.error(e.getMessage(), e);
}
}
if(connection != null){
try {
connection.disconnect();
} catch (Exception e) {
log.error(e.getMessage(), e);
}
}
}
return response.toString();
}
/**
* http post请求
* @param url 链接
* @param params 参数内容，json格式或"name=smy&age=18&..."表单格式
* @return 请求返回内容
*/
public static String doPost(String url, @Nullable String params) {
/// 确定请求参数类型
String ContentType = "application/json";
try{
JSONObject.parseObject(params);
}catch (Exception e){
ContentType = "application/x-www-form-urlencoded";
}
StringBuilder response = new StringBuilder();
HttpURLConnection connection = null;
OutputStream outputStream = null;
InputStream inputStream = null;
BufferedReader br = null;
try {
connection= (HttpURLConnection) new URL(url).openConnection();
connection.setRequestMethod("POST");
connection.setConnectTimeout(15000);
connection.setReadTimeout(15000);
/// 设置请求头部
connection.setRequestProperty("appKey", "123456");
/// 设置是否可读取
connection.setDoOutput(true);
/// 设置响应可读取
connection.setDoInput(true);
/// 设置返回数据格式
connection.setRequestProperty("Accept", "*/*");
/// 设置请求参数类型
connection.setRequestProperty("Content-Type", ContentType);
/// 设置请求参数内容,并发送请求
if(params != null && !params.isEmpty()) {
outputStream = connection.getOutputStream();
outputStream.write(params.getBytes(StandardCharsets.UTF_8));
outputStream.flush();
}
/// 读取服务端响应
if(connection.getResponseCode() == 200){
inputStream = connection.getInputStream();
}else{
inputStream = connection.getErrorStream();
}
if(inputStream != null){
br = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
String line;
if((line = br.readLine()) != null){
response.append(line);
}
}
} catch (IOException e) {
log.error(e.getMessage(), e);
} finally {
if(br != null){
try {
br.close();
} catch (IOException e) {
log.error(e.getMessage(), e);
}
}
if(outputStream != null){
try {
outputStream.close();
} catch (IOException e) {
log.error(e.getMessage(), e);
}
}
if(inputStream != null){
try {
inputStream.close();
} catch (IOException e) {
log.error(e.getMessage(), e);
}
}
if(connection != null){
try {
connection.disconnect();
} catch (Exception e) {
log.error(e.getMessage(), e);
}
}
}
return response.toString();
}
/*****************************************
* 测试代码
****************************************/
public static void main(String[] strs){
// String response = HttpUtil.doGet("http://localhost:8081/car/getById/2");
// System.out.println("请求返回：\n" + response);
String url = "http://localhost:8081/car/getByConds1";
// String params = "brand=vw&type=oil";
String params = "{\"brand\":\"vw\", \"type\":\"oil\"}";
String str = HttpUtil.doPost(url, params);
System.out.println(str.toString());
JSONObject jsonObject = JSONObject.parseObject(str);
}
}
二、基于HttpClient的请求发送
Apache HttpClient 官网：http://hc.apache.org/httpcomponents-client-5.1.x/
下述示例代码基于Apache httpClient4.5编写：
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.*;
import java.util.Map.Entry;
import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
public class HttpUtil {
public static String doGet(String url) {
CloseableHttpClient httpClient = null;
CloseableHttpResponse httpResponse = null;
String result = "";
try {
httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet(url);
httpGet.setHeader("Authorization", "Bearer 88888888-4444-4444-4444-cccccccccccc");
RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(35000)
.setConnectionRequestTimeout(35000)
.setSocketTimeout(60000)
.build();
httpGet.setConfig(requestConfig);
httpResponse = httpClient.execute(httpGet);
HttpEntity entity = httpResponse .getEntity();
result = EntityUtils.toString(entity);
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (null != httpResponse ) {
try {
httpResponse.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (null != httpClient) {
try {
httpClient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return result;
}
public static String doPost(String url, Map<String, Object> paramMap) {
CloseableHttpClient httpClient = null;
CloseableHttpResponse httpResponse = null;
String result = "";
httpClient = HttpClients.createDefault();
HttpPost httpPost = new HttpPost(url);
/// 设置请求时限参数
RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(35000)
.setConnectionRequestTimeout(35000)
.setSocketTimeout(60000)
.build();
httpPost.setConfig(requestConfig);
/// 设置请求头部数据
httpGet.setHeader("Authorization", "Bearer 88888888-4444-4444-4444-cccccccccccc");
/// 设置请求参数类型
httpPost.addHeader("Content-Type", "application/x-www-form-urlencoded");
/// 封装post请求参数
if (null != paramMap && paramMap.size() > 0) {
List<NameValuePair> nvps = new ArrayList<NameValuePair>();
Set<Entry<String, Object>> entrySet = paramMap.entrySet();
Iterator<Entry<String, Object>> iterator = entrySet.iterator();
while (iterator.hasNext()) {
Entry<String, Object> mapEntry = iterator.next();
nvps.add(new BasicNameValuePair(mapEntry.getKey(), mapEntry.getValue().toString()));
}
try {
httpPost.setEntity(new UrlEncodedFormEntity(nvps, "UTF-8"));
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
try {
/// 发送请求，获取响应
httpResponse = httpClient.execute(httpPost);
HttpEntity entity = httpResponse.getEntity();
result = EntityUtils.toString(entity);
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (null != httpResponse) {
try {
httpResponse.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (null != httpClient) {
try {
httpClient.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return result;
}
}
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