RPC (3): HttpClient implements RPC GET request

1HttpClientIntroduction

The java.net package in the JDK provides basic functions for user HTTP access, but it lacks flexibility or functions required by many applications.

HttpClient was originally a sub-project of Apache Jakarta Common. It is used to provide an efficient, up-to-date, feature-rich client programming toolkit that supports the HTTP protocol, and it supports the latest version of the HTTP protocol. Became a top project in 2007.

Popular explanation: HttpClient can use Java code to complete standard HTTP requests and responses.

2 Create a new server project

Create a new project httpclient_rpc_server

2.1 Modify maven configuration file

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.3.2.RELEASE</version>
                <scope>import</scope>
                <type>pom</type>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

2.2 Create a new controller

package com.example.httpclientserver.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class TestController {

    /*
    * 带参数的get请求
    */
    @RequestMapping(value="/params", produces = {"application/json;charset=UTF-8"})
    @ResponseBody
    public String params(String name, String password){
        System.out.println("name - " + name + " ; password - " + password);
        return "{\"msg\":\"登录成功\", \"user\":{\"name\":\""+name+"\",\"password\":\""+password+"\"}}";
    }
    /*
     * 不带参数的get请求
     */
    @RequestMapping(value="/test",produces = {"application/json;charset=UTF-8"})
    @ResponseBody
    public String test(){
        return "{\"msg\":\"处理返回\"}";
    }
}

2.3 Create a new launcher

package com.example.httpclientserver;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class ServerApp {
    public static void main(String[] args) {
        SpringApplication.run(ServerApp.class, args);
    }
}

2.4 Modify the port in application.yml (optional operation)

server:
  port: 80

2.5 Testing

3 Create a new client project

Create a new client project httpclient_rpc_client

3.1 Add maven dependencies

    <dependencies>
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
            <version>4.5.12</version>
        </dependency>
    </dependencies>

3.2 Create a new main class for httpclient access

package com.example.httpclient;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.ArrayList;
import java.util.List;

public class TestHttpClient {
    public static void main(String[] args) throws Exception {
        //访问无参数GET请求
        testGetNoParams();
        //访问有参数GET请求
        testGetNoParams();
    }

    /**
     * 有参数GET请求
     * @throws IOException
     */
    public static void testGetParams() throws IOException, URISyntaxException {
        HttpClient client = HttpClients.createDefault();
        // 基于Builder构建请求地址
        URIBuilder builder = new URIBuilder("http://localhost:80/params");
        // 基于单参数传递，构建请求地址
//        builder.addParameter("name", "bjsxt");
//        builder.addParameter("password", "admin123");
//        URI uri = builder.build();

        // 基于多参数传递，构建请求地址
        List<NameValuePair> nvps = new ArrayList<NameValuePair>();
        nvps.add(new BasicNameValuePair("name","bjsxt"));
        nvps.add(new BasicNameValuePair("password", "admin123"));
        builder.addParameters(nvps);
        URI uri = builder.build();
        System.out.println(uri.toASCIIString());

        String result = EntityUtils.toString(client.execute(new HttpGet(uri)).getEntity());
        System.out.println(result);
    }

    /**
     * 无参数GET请求
     * 使用浏览器，访问网站的过程是：
     *  1、 打开浏览器
     *  2、 输入地址
     *  3、 访问
     *  4、 看结果
     * 使用HttpClient，访问WEB服务的过程：
     *  1、 创建客户端，相当于打开浏览器
     *  2、 创建请求地址， 相当于输入地址
     *  3、 发起请求， 相当于访问网站（回车键）
     *  4、 处理响应结果， 相当于浏览器显示结果
     */
    public static void testGetNoParams() throws IOException {
        // 创建客户端对象
        HttpClient client = HttpClients.createDefault();
        // 创建请求地址
        HttpGet get = new HttpGet("http://localhost:80/test");
        // 发起请求，接收响应对象
        HttpResponse response = client.execute(get);
        // 获取响应体。 响应数据是一个基于HTTP协议标准字符串封装的对象。
        // 所以，响应体和响应头，都是封装的HTTP协议数据。直接使用可能有乱码或解析错误
        HttpEntity entity = response.getEntity();

        // 通过HTTP实体工具类，转换响应体数据。 使用的字符集是UTF-8
        String responseString = EntityUtils.toString(entity, "UTF-8");

        System.out.println("服务器响应数据是 - [ " + responseString + " ]");

        // 回收资源
        client = null;

    }
}

There are two parameter-based request methods. One is based on single parameter transfer and constructs the request address, as follows:

        // 基于单参数传递，构建请求地址
        builder.addParameter("name", "bjsxt");
        builder.addParameter("password", "admin123");
        URI uri = builder.build();

One is to build the request address based on multi-parameter passing, as follows:

        // 基于多参数传递，构建请求地址
        List<NameValuePair> nvps = new ArrayList<NameValuePair>();
        nvps.add(new BasicNameValuePair("name","bjsxt"));
        nvps.add(new BasicNameValuePair("password", "admin123"));
        builder.addParameters(nvps);
        URI uri = builder.build();

4 tests

Start httpclient_rpc_server and httpclient_rpc_client. The httpclient_rpc_client console output is as follows:

GET request successful.