一、HttpClient

两个系统间如何互相访问？两个tomcat上的项目如何互相访问？

       采用HttpClient实现跨系统的接口调用。

介绍：

官网：http://hc.apache.org/index.html

现在也叫：HttpComponents

HttpClient可以发送get、post、put、delete、...等请求

使用：

导入坐标

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.4</version>
</dependency>

//1、使用HttpClient发起Get请求
public class DoGET {

    public static void main(String[] args) throws Exception {
        // 创建Httpclient对象,相当于打开了浏览器
        CloseableHttpClient httpclient = HttpClients.createDefault();

        // 创建HttpGet请求，相当于在浏览器输入地址
        HttpGet httpGet = new HttpGet("http://www.baidu.com/");

        CloseableHttpResponse response = null;
        try {
            // 执行请求，相当于敲完地址后按下回车。获取响应
            response = httpclient.execute(httpGet);
            // 判断返回状态是否为200
            if (response.getStatusLine().getStatusCode() == 200) {
                // 解析响应，获取数据
                String content = EntityUtils.toString(response.getEntity(), "UTF-8");
                System.out.println(content);
            }
        } finally {
            if (response != null) {
                // 关闭资源
                response.close();
            }
            // 关闭浏览器
            httpclient.close();
        }

    }
}


//2、使用HttpClient发起带参数的Get请求
public class DoGETParam {

    public static void main(String[] args) throws Exception {
        // 创建Httpclient对象
        CloseableHttpClient httpclient = HttpClients.createDefault();
        // 创建URI对象，并且设置请求参数
        URI uri = new URIBuilder("http://www.baidu.com/s").setParameter("wd", "java").build();
        
        // 创建http GET请求
        HttpGet httpGet = new HttpGet(uri);

        // HttpGet get = new HttpGet("http://www.baidu.com/s?wd=java");
        
        CloseableHttpResponse response = null;
        try {
            // 执行请求
            response = httpclient.execute(httpGet);
            // 判断返回状态是否为200
            if (response.getStatusLine().getStatusCode() == 200) {
                // 解析响应数据
                String content = EntityUtils.toString(response.getEntity(), "UTF-8");
                System.out.println(content);
            }
        } finally {
            if (response != null) {
                response.close();
            }
            httpclient.close();
        }
    }
}


//3、使用HttpClient发起POST请求
public class DoPOST {
    public static void main(String[] args) throws Exception {
        // 创建Httpclient对象
        CloseableHttpClient httpclient = HttpClients.createDefault();
        // 创建http POST请求
        HttpPost httpPost = new HttpPost("http://www.oschina.net/");
        // 把自己伪装成浏览器。否则开源中国会拦截访问
        httpPost.setHeader("User-Agent", "Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36");

        CloseableHttpResponse response = null;
        try {
            // 执行请求
            response = httpclient.execute(httpPost);
            // 判断返回状态是否为200
            if (response.getStatusLine().getStatusCode() == 200) {
                // 解析响应数据
                String content = EntityUtils.toString(response.getEntity(), "UTF-8");
                System.out.println(content);
            }
        } finally {
            if (response != null) {
                response.close();
            }
            // 关闭浏览器
            httpclient.close();
        }

    }
}


//4、使用HttpClient发起带有参数的POST请求
public class DoPOSTParam {

    public static void main(String[] args) throws Exception {
        // 创建Httpclient对象
        CloseableHttpClient httpclient = HttpClients.createDefault();
        // 创建http POST请求，访问开源中国
        HttpPost httpPost = new HttpPost("http://www.oschina.net/search");

        // 根据开源中国的请求需要，设置post请求参数
        List<NameValuePair> parameters = new ArrayList<NameValuePair>(0);
        parameters.add(new BasicNameValuePair("scope", "project"));
        parameters.add(new BasicNameValuePair("q", "java"));
        parameters.add(new BasicNameValuePair("fromerr", "8bDnUWwC"));
        // 构造一个form表单式的实体
        UrlEncodedFormEntity formEntity = new UrlEncodedFormEntity(parameters);
        // 将请求实体设置到httpPost对象中
        httpPost.setEntity(formEntity);

        CloseableHttpResponse response = null;
        try {
            // 执行请求
            response = httpclient.execute(httpPost);
            // 判断返回状态是否为200
            if (response.getStatusLine().getStatusCode() == 200) {
                // 解析响应体
                String content = EntityUtils.toString(response.getEntity(), "UTF-8");
                System.out.println(content);
            }
        } finally {
            if (response != null) {
                response.close();
            }
            // 关闭浏览器
            httpclient.close();
        }
    }
}

 二、RestTemplate

RestTemplate是Spring提供的用于访问Rest服务的客户端，RestTemplate提供了多种便捷访问远程Http服务的方法

HTTP开发是用apache的HttpClient开发，代码复杂，还得操心资源回收等。代码很复杂，冗余代码多。

导入坐标

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

创建RestTemplate对象

@Configuration//加上这个注解作用，可以被Spring扫描
public class RestTemplateConfig {
    /**
     * 创建RestTemplate对象，将RestTemplate对象的生命周期的管理交给Spring
     * @return
     */
    @Bean
    public RestTemplate restTemplate(){
        RestTemplate restTemplate = new RestTemplate();
        //主要解决中文乱码
        restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(StandardCharsets.UTF_8));
        return restTemplate;
    }
}

RestTempController

import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.client.RestTemplate;

import javax.annotation.Resource;

@RestController
@RequestMapping("/consumer")
public class ConsumerController {
    // 从Spring的容器中获取restTemplate
    @Resource
    private RestTemplate restTemplate;

    /**
     * 通过Get请求，保存数据
     */
    @GetMapping("/{id}")
    public ResponseEntity<String> findById(@PathVariable Integer id){
        //发起远程请求:通过RestTemplate发起get请求
        ResponseEntity<String> entity = restTemplate.getForEntity("http://localhost:8090/goods2/1", String.class);
        System.out.println("entity.getStatusCode():"+entity.getStatusCode());
        System.out.println(entity.getBody());
        return  entity;
    }

    /**
     * 通过Post请求，保存数据
     */
    @PostMapping
    public ResponseEntity<String> saveGoods(@RequestBody Goods goods){
        //通过RestTemplate发起远程请求
        /**
         * 第一个参数：远程地址URI
         * 第二个参数：数据
         * 第三个参数：返回值类型
         */
        ResponseEntity<String> entity = restTemplate.postForEntity("http://localhost:8090/goods2", goods, String.class);
        System.out.println("entity.getStatusCode():"+entity.getStatusCode());
        System.out.println(entity.getBody());
        return  entity;
    }

    @PutMapping
    public ResponseEntity<String> updateGoods(@RequestBody Goods goods){
        restTemplate.put("http://localhost:8090/goods2",goods);
        return new ResponseEntity<>("修改成功", HttpStatus.OK);
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<String> deleteById(@PathVariable Integer id){
        restTemplate.delete("http://localhost:8090/goods2/"+id);
        return new ResponseEntity<>("删除成功", HttpStatus.OK);
    }
}