概述

Java可以实现HTTP请求的方法有很多，下面我列举了一些：

  1. RestTemplate，这个是Spring提供的，可以减少引入的依赖
  2. HTTPClient
  3. Hutool工具类库，这个使用最方便且有详细的中文文档
  4. OkHttp

要测试的接口

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package com.ledao.springbootdemo.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:30
 */
@RestController
@RequestMapping("/hello")
public class HelloController {

    @GetMapping("/doGet")
    public String doGet(String city) {
        return "Hello " + city;
    }

    @PostMapping("/doPost")
    public String doPost(String str) {
        return str;
    }
}

RestTemplate

介绍

RestTemplate是Spring用于同步client端的核心类，简化了与http服务的通信，并满足RestFul原则，程序代码可以给它提供URL，并提取结果

代码实现

get请求

参数既可以直接拼接在url中，也可以使用Map设置并传入（使用Map感觉更麻烦）

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package com.ledao.springbootdemo;

import org.springframework.web.client.RestTemplate;

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

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) {
        //创建RestTemplate对象
        RestTemplate restTemplate = new RestTemplate();
        //请求的url,这里需要拼接参数,不然无法传参成功
        String url = "http://localhost:8080/hello/doGet?city={city}";
        //设置参数
        Map<String, String> params = new HashMap<>(16);
        params.put("city", "北京");
        //得到请求的结果
        String result = restTemplate.getForObject(url, String.class, params);
        //打印结果
        System.out.println(result);
    }
}

自动拼接Map中的参数，url中只需要写接口

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package com.ledao.springbootdemo;

import org.springframework.web.client.RestTemplate;

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

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) {
        //创建RestTemplate对象
        RestTemplate restTemplate = new RestTemplate();
        //设置参数
        Map<String, Object> params = new HashMap<>(16);
        params.put("city", "北京");
        //请求的url
        StringBuilder url = new StringBuilder("http://localhost:8080/hello/doGet");
        //用于记录当前是第几个参数
        int index = 0;
        //开始拼接参数
        for (String key : params.keySet()) {
            //第一个参数前要加上一个问号
            if (index == 0) {
                url.append("?").append(key).append("=").append(params.get(key)).append("&");
            } else {
                url.append(key).append("=").append(params.get(key)).append("&");
            }
            index++;
        }
        //得到请求的结果
        String result = restTemplate.getForObject(url.toString(), String.class);
        //打印结果
        System.out.println(result);
    }
}

封装拼接参数的代码

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package com.ledao.springbootdemo.util;

import java.util.Map;

/**
 * @author LeDao
 * @company
 * @create 2023-01-16 19:27
 */
public class MyUtil {

    /**
     * 获得自动拼接参数后的url
     *
     * @param url
     * @param params
     * @return
     */
    public static String getUrl(String url, Map<String, Object> params) {
        //请求的url
        StringBuilder resultUrl = new StringBuilder(url);
        //用于记录当前是第几个参数
        int index = 0;
        //开始拼接参数
        for (String key : params.keySet()) {
            //第一个参数前要加上一个问号
            if (index == 0) {
                resultUrl.append("?").append(key).append("=").append(params.get(key)).append("&");
            } else {
                resultUrl.append(key).append("=").append(params.get(key)).append("&");
            }
            index++;
        }
        return resultUrl.toString();
    }
}

使用封装的方法

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package com.ledao.springbootdemo;

import com.ledao.springbootdemo.util.MyUtil;
import org.springframework.web.client.RestTemplate;

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

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) {
        //创建RestTemplate对象
        RestTemplate restTemplate = new RestTemplate();
        //设置参数
        Map<String, Object> params = new HashMap<>(16);
        params.put("city", "北京");
        //得到请求的结果
        String result = restTemplate.getForObject(MyUtil.getUrl("http://localhost:8080/hello/doGet", params), String.class);
        //打印结果
        System.out.println(result);
    }
}

post请求

这里有个坑，不能使用HashMap传参，要使用LinkedMultiValueMap

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package com.ledao.springbootdemo;

import org.springframework.util.LinkedMultiValueMap;
import org.springframework.web.client.RestTemplate;

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) {
        //创建RestTemplate对象
        RestTemplate restTemplate = new RestTemplate();
        //请求的url
        String url = "http://localhost:8080/hello/doPost";
        //设置参数
        LinkedMultiValueMap<String, Object> params = new LinkedMultiValueMap<>();
        params.add("str", "12345678910");
        //得到请求的结果
        String result = restTemplate.postForObject(url, params, String.class);
        //打印结果
        System.out.println(result);
    }
}

HTTPClient

引入依赖

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<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.14</version>
</dependency>

代码实现

工具类

把get和post请求封装成工具类以便调用

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package com.ledao.springbootdemo.util;

import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
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.client.utils.URIBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;
import java.net.URISyntaxException;
import java.util.List;
import java.util.Map;

/**
 * HttpClient工具类
 *
 * @author LeDao
 * @company
 * @create 2023-01-12 6:13
 */
public class HttpClientUtil {

    /**
     * 发送get请求
     *
     * @param url    请求的url
     * @param params 参数
     * @return
     * @throws Exception
     */
    public static String sendGet(String url, List<NameValuePair> params) throws Exception {
        //创建一个HttpClient对象
        CloseableHttpClient httpClient = HttpClients.createDefault();
        //创建一个url对象
        URIBuilder builder = new URIBuilder(url);
        //设置参数
        builder.addParameters(params);
        //创建GET请求
        HttpGet get = new HttpGet(builder.build());
        //执行请求
        CloseableHttpResponse response = httpClient.execute(get);
        //状态码
        int code = response.getStatusLine().getStatusCode();
        System.out.println(code);
        //得到的结果
        String content = EntityUtils.toString(response.getEntity(), "utf-8");
        //关闭连接
        response.close();
        httpClient.close();
        //返回结果
        return content;
    }

    /**
     * 发送post请求
     *
     * @param url 请求的url
     * @param params 参数
     * @return
     * @throws Exception
     */
    public static String sendPost(String url, List<NameValuePair> params) throws Exception {
        //创建一个HttpClient对象
        CloseableHttpClient httpClient = HttpClients.createDefault();
        //创建一个url对象
        URIBuilder builder = new URIBuilder(url);
        //设置参数
        builder.addParameters(params);
        //创建GET请求
        HttpPost post = new HttpPost(builder.build());
        //执行请求
        CloseableHttpResponse response = httpClient.execute(post);
        //状态码
        int code = response.getStatusLine().getStatusCode();
        System.out.println(code);
        //得到的结果
        String content = EntityUtils.toString(response.getEntity(), "utf-8");
        //关闭连接
        response.close();
        httpClient.close();
        //返回结果
        return content;
    }
}

测试

get请求
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package com.ledao.springbootdemo;

import com.ledao.springbootdemo.util.HttpClientUtil;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;

import java.util.ArrayList;
import java.util.List;

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) throws Exception {
        //请求的url
        String url = "http://localhost:8080/hello/doGet";
        //设置参数
        List<NameValuePair> params = new ArrayList<>();
        params.add(new BasicNameValuePair("city", "北京"));
        //得到请求的结果
        String content = HttpClientUtil.sendGet(url, params);
        //打印结果
        System.out.println(content);
    }
}
post请求
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package com.ledao.springbootdemo;

import com.ledao.springbootdemo.util.HttpClientUtil;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;

import java.util.ArrayList;
import java.util.List;

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) throws Exception {
        //请求的url
        String url = "http://localhost:8080/hello/doPost";
        //设置参数
        List<NameValuePair> params = new ArrayList<>();
        params.add(new BasicNameValuePair("str", "123456"));
        //得到请求的结果
        String content = HttpClientUtil.sendPost(url, params);
        //打印结果
        System.out.println(content);
    }
}

Hutool工具类库

引入依赖

下面这个依赖是Hutool工具类库完整依赖，如果还使用到Hutool的其它工具类就使用完整依赖

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<!-- https://mvnrepository.com/artifact/cn.hutool/hutool-all -->
<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>5.8.11</version>
</dependency>

下面这个依赖是Hutool工具类库HTTP请求的依赖，如果只使用到Hutool工具类库的HTTP请求，就选择下面这个

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<!-- https://mvnrepository.com/artifact/cn.hutool/hutool-http -->
<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-http</artifactId>
    <version>5.8.11</version>
</dependency>

代码实现

如果要实现更复杂的请求可以去使用Http请求-HttpRequest，下面代码只是传了参数然后发起请求

get请求

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package com.ledao.springbootdemo;

import cn.hutool.http.HttpUtil;

import java.util.HashMap;

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) {
        //要请求的url
        String url = "http://localhost:8080/hello/doGet";
        //设置参数
        HashMap<String, Object> paramMap = new HashMap<>(16);
        paramMap.put("city", "北京");
        //发起请求
        String str = HttpUtil.get(url, paramMap);
        //打印结果
        System.out.println(str);
    }
}

post请求

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package com.ledao.springbootdemo;

import cn.hutool.http.HttpUtil;

import java.util.HashMap;

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) {
        //要请求的url
        String url = "http://localhost:8080/hello/doPost";
        //设置参数
        HashMap<String, Object> paramMap = new HashMap<>(16);
        paramMap.put("str", "北京");
        //发起请求
        String str = HttpUtil.post(url, paramMap);
        //打印结果
        System.out.println(str);
    }
}

OkHttp

引入依赖

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<!-- https://mvnrepository.com/artifact/com.squareup.okhttp3/okhttp -->
<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.10.0</version>
</dependency>

代码实现

工具类

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package com.ledao.springbootdemo.util;

import okhttp3.FormBody;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

import java.io.IOException;

/**
 * OkHttp工具类
 *
 * @author LeDao
 * @company
 * @create 2023-01-12 7:00
 */
public class OkHttpUtil {
    
    /**
     * 发送get请求
     *
     * @param url 请求的url
     * @return
     * @throws IOException
     */
    public static String sendGet(String url) throws IOException {
        OkHttpClient okHttpClient = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .get()
                .build();
        try (Response response = okHttpClient.newCall(request).execute()) {
            return response.body().string();
        }
    }

    /**
     * 发送post请求
     *
     * @param url      请求的url
     * @param formBody 携带参数
     * @return
     * @throws IOException
     */
    public static String sendPost(String url, FormBody formBody) throws IOException {
        OkHttpClient okHttpClient = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .post(formBody)
                .build();
        try (Response response = okHttpClient.newCall(request).execute()) {
            return response.body().string();
        }
    }
}

测试

get请求

参数拼接在url中，需要自己手动拼接，也可以使用上面RestTemplate中封装的代码来自动拼接参数

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package com.ledao.springbootdemo;

import com.ledao.springbootdemo.util.OkHttpUtil;

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) throws Exception {
        //请求的url
        String url = "http://localhost:8080/hello/doGet?city=北京";
        //得到请求的结果
        String result = OkHttpUtil.sendGet(url);
        //打印结果
        System.out.println(result);
    }
}
post请求
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package com.ledao.springbootdemo;

import com.ledao.springbootdemo.util.OkHttpUtil;
import okhttp3.FormBody;

/**
 * @author LeDao
 * @company
 * @create 2023-01-12 5:45
 */
public class Test {

    public static void main(String[] args) throws Exception {
        //请求的url
        String url = "http://localhost:8080/hello/doPost";
        //设置参数,有几个参数就有几个add()
        FormBody formBody = new FormBody.Builder()
                .add("str", "12345678910")
                .build();
        //得到请求的结果
        String result = OkHttpUtil.sendPost(url, formBody);
        //打印结果
        System.out.println(result);
    }
}