在写网络程序的时候，经常会有从网址获取数据的需求，本文介绍一种Java发送http请求的工具–HttpClient。
HttpClient的介绍
HttpClient最基本的功能就是执行http方法，执行http方法包括了一次或者几次HTTP请求和相应的变化，通常也是通过HttpClient来处理的。只要用户提供一个request的对象，HttpClient就会将用户的请求发送到目标服务器上，并且返回一个respone对象，如果没有执行成功将抛出一个异常。通过文档的介绍我们可以知道，发送HTTP请求一般可以分为以下步骤：
1.取得HttpClient对象
2.封装http请求
3.执行http请求
4.处理结果
其中可以发送的请求类型有GET, HEAD, POST, PUT, DELETE, TRACE 和 OPTIONS
官方文档中的示例
//1.获得一个httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();
//2.生成一个get请求
HttpGet httpget = new HttpGet("http://localhost/");
//3.执行get请求并返回结果
CloseableHttpResponse response = httpclient.execute(httpget);
try {
//4.处理结果
} finally {
response.close();
}
介绍一下最常用的HttpGet和HttpPost。
RESTful提倡，通过HTTP请求对应的POST、GET、PUT、DELETE来完成对应的CRUD操作。
所以本文介绍一下通过GET获取数据和POST提交数据的实现方法。
发送HttpGet
先介绍发送HttpGet请求
/**
* 发送HttpGet请求
* @param url
* @return
*/
public static String sendGet(String url) {
//1.获得一个httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();
//2.生成一个get请求
HttpGet httpget = new HttpGet(url);
CloseableHttpResponse response = null;
try {
//3.执行get请求并返回结果
response = httpclient.execute(httpget);
} catch (IOException e1) {
e1.printStackTrace();
}
String result = null;
try {
//4.处理结果，这里将结果返回为字符串
HttpEntity entity = response.getEntity();
if (entity != null) {
result = EntityUtils.toString(entity);
}
} catch (ParseException | IOException e) {
e.printStackTrace();
} finally {
try {
response.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return result;
}
发送HttpPost
发送HttpPost的方法和发送HttpGet很类似，只是将请求类型给位HttpPost即可。
代码如下
/**
* 发送不带参数的HttpPost请求
* @param url
* @return
*/
public static String sendPost(String url) {
//1.获得一个httpclient对象
CloseableHttpClient httpclient = HttpClients.createDefault();
//2.生成一个post请求
HttpPost httppost = new HttpPost(url);
CloseableHttpResponse response = null;
try {
//3.执行get请求并返回结果
response = httpclient.execute(httppost);
} catch (IOException e) {
e.printStackTrace();
}
//4.处理结果，这里将结果返回为字符串
HttpEntity entity = response.getEntity();
String result = null;
try {
result = EntityUtils.toString(entity);
} catch (ParseException | IOException e) {
e.printStackTrace();
}
return result;
}
带参数的HttpPost，发送带参数的HttpPost
HttpClient通过UrlEncodedFormEntity，来提交带参数的请求
将需要提交的参数放在map里
代码如下
/**
* 发送HttpPost请求，参数为map
* @param url
* @param map
* @return
*/
public static String sendPost(String url, Map<String, String> map) {
CloseableHttpClient httpclient = HttpClients.createDefault();
List<NameValuePair> formparams = new ArrayList<NameValuePair>();
for (Map.Entry<String, String> entry : map.entrySet()) {
//给参数赋值
formparams.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
}
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formparams, Consts.UTF_8);
HttpPost httppost = new HttpPost(url);
httppost.setEntity(entity);
CloseableHttpResponse response = null;
try {
response = httpclient.execute(httppost);
} catch (IOException e) {
e.printStackTrace();
}
HttpEntity entity1 = response.getEntity();
String result = null;
try {
result = EntityUtils.toString(entity1);
} catch (ParseException | IOException e) {
e.printStackTrace();
}
return result;
}
完成代码如下，用到的jar包有httpclient-4.5.1.jar，httpcore-4.4.3.jar，
依赖的jar有commons-logging-1.2.jar
注意是Apache HttpClient，不是commons-httpclient
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import org.apache.http.Consts;
import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.ParseException;
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;
/**
* @author GWCheng
*
*/
public class HttpUtil {
private static final CloseableHttpClient httpclient = HttpClients.createDefault();
/**
* 发送HttpGet请求
* @param url
* @return
*/
public static String sendGet(String url) {
HttpGet httpget = new HttpGet(url);
CloseableHttpResponse response = null;
try {
response = httpclient.execute(httpget);
} catch (IOException e1) {
e1.printStackTrace();
}
String result = null;
try {
HttpEntity entity = response.getEntity();
if (entity != null) {
result = EntityUtils.toString(entity);
}
} catch (ParseException | IOException e) {
e.printStackTrace();
} finally {
try {
response.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return result;
}
/**
* 发送HttpPost请求，参数为map
* @param url
* @param map
* @return
*/
public static String sendPost(String url, Map<String, String> map) {
List<NameValuePair> formparams = new ArrayList<NameValuePair>();
for (Map.Entry<String, String> entry : map.entrySet()) {
formparams.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
}
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formparams, Consts.UTF_8);
HttpPost httppost = new HttpPost(url);
httppost.setEntity(entity);
CloseableHttpResponse response = null;
try {
response = httpclient.execute(httppost);
} catch (IOException e) {
e.printStackTrace();
}
HttpEntity entity1 = response.getEntity();
String result = null;
try {
result = EntityUtils.toString(entity1);
} catch (ParseException | IOException e) {
e.printStackTrace();
}
return result;
}
/**
* 发送不带参数的HttpPost请求
* @param url
* @return
*/
public static String sendPost(String url) {
HttpPost httppost = new HttpPost(url);
CloseableHttpResponse response = null;
try {
response = httpclient.execute(httppost);
} catch (IOException e) {
e.printStackTrace();
}
HttpEntity entity = response.getEntity();
String result = null;
try {
result = EntityUtils.toString(entity);
} catch (ParseException | IOException e) {
e.printStackTrace();
}
return result;
}
}
测试用例
服务器端代码
@Controller
@RequestMapping("/test")
// /test/**
public class TestController {
// /test/view post 提交数据，模拟表单
@RequestMapping(value = "/view", method = RequestMethod.POST)
public void viewTest(PrintWriter out, HttpServletResponse response, @RequestParam("param1") String param1,
@RequestParam("param2") String param2) {
response.setContentType("application/json;charset=UTF-8");
Gson gson = new GsonBuilder().create();
Map<String, Object> map = new HashMap<String, Object>();
map.put("param1", param1);
map.put("param2", param2);
System.out.println(gson.toJson(map));
out.print(gson.toJson(map));
}
// /test/view?param1=aaa¶m2=bbb get
@RequestMapping(value = "/view", method = RequestMethod.GET)
public void viewTest3(PrintWriter out, HttpServletResponse response, @RequestParam("param1") String param1,
@RequestParam("param2") String param2) {
response.setContentType("application/json;charset=UTF-8");
Gson gson = new GsonBuilder().create();
Map<String, Object> map = new HashMap<String, Object>();
map.put("param1", param1);
map.put("param2", param2);
System.out.println(gson.toJson(map));
out.print(gson.toJson(map));
}
// /test/view2/{courseId}
@RequestMapping(value = "/view2/{param}", method = RequestMethod.GET)
public void viewTest1(PrintWriter out, HttpServletResponse response, @PathVariable("param") String param) {
response.setContentType("application/json;charset=UTF-8");
Gson gson = new GsonBuilder().create();
Map<String, Object> map = new HashMap<String, Object>();
map.put("param", param);
out.print(gson.toJson(map));
}
// /test/view3
@RequestMapping(value = "/view3", method = RequestMethod.POST)
public void viewTest2(PrintWriter out, HttpServletResponse response) {
response.setContentType("application/json;charset=UTF-8");
Gson gson = new GsonBuilder().create();
Map<String, Object> map = new HashMap<String, Object>();
map.put("status", "success");
out.print(gson.toJson(map));
}
}
测试代码
public class HttpClientTest {
@Test
public void testGet() {
//百度天气的api
//String url1 = "http://api.map.baidu.com/telematics/v3/weather?location=%E5%8C%97%E4%BA%AC&output=json&ak=W69oaDTCfuGwzNwmtVvgWfGH";
String url1 = "http://localhost:8080/wechat/test/view2/你好世界";
String result1 = HttpUtil.sendGet(url1);
System.out.println(result1);
//输出{"param":"你好世界"}
}
@Test
public void testPost() throws UnsupportedEncodingException{
String url = "http://localhost:8080/wechat/test/view";
Map<String,String> map = new HashMap<String,String>();
map.put("param1", "你好世界");
map.put("param2", "哈哈");
String result = HttpUtil.sendPost(url, map);
System.out.println(result);
//输出结果{"param1":"你好世界","param2":"哈哈"}
}
@Test
public void testPost1() throws UnsupportedEncodingException{
String url = "http://localhost:8080/wechat/test/view3";
String result = HttpUtil.sendPost(url);
System.out.println(result);
//输出结果{"status":"success"}
}
}
建议通过HttpGet获取信息，HttpPost提交信息，
而HttpGet获取信息时需要提交的参数一般会在url中体现，
或者以？传参，或者在url中传参，所以就没写HttpGet带参数的。
也希望大家能遵循Http的设计原则，通过HttpGet, HttpPost, HttpPut, HttpDelete,
来实现获取数据，提交数据，修改数据，和删除数据的方法。
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本文来自 GW_Cheng 的CSDN 博客 ，全文地址请点击：https://blog.csdn.net/frankcheng5143/article/details/50070591
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