使用Spring的RestTemplate进行接口调用

引自：http://www.zimug.com/

1.常见的http服务的通信方式

经常使用的方式有HttpClient、OkHttp、RestTemplate。其中RestTemplate是一种更优雅的调用RESTful服务的方式。

RestTemplate使用了模版方法的设计模式，借助 RestTemplate，Spring应用可以很方便地访问REST资源。

2.主要的方法

get请求常用方法：
getForObject  //返回响应内容
getForEntity  //返回响应体

post请求常用方法：
postForObject  //返回响应内容
postForEntity  //返回响应体

二合一的方法：
exchange //该方法的参数可以设置不同请求方法，可以选择get或者post

3.客户端和服务端

3.1 服务端

新建一个spring-boot项目。引入依赖。

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>fastjson</artifactId>
        <version>1.2.73</version>
    </dependency>
</dependencies>

server:
  port: 8090

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

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedReader;
import java.io.IOException;
import java.util.Enumeration;

@RestController
@CrossOrigin
public class IndexController {

    @GetMapping("/getData")
    public String getData() {
        return "hello, get method";
    }

    @PostMapping("/postData")
    public String postData(HttpServletRequest request, HttpServletResponse response) throws IOException {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        System.out.println(request.getRemoteUser());
        System.out.println(request.getAuthType());
        System.out.println(request.getContentType());
        System.out.println(request.getContextPath());
        System.out.println(request.getRemoteAddr());
        System.out.println(request.getRemoteHost());
        System.out.println(request.getRemotePort());
         //1.读取header中的数据，通过key来获取
        System.out.println(request.getHeader("username"));
        System.out.println("=====================");
        BufferedReader reader = request.getReader();
        //2.读取body中的数据
        String line = null;
        while ((line = reader.readLine()) != null){
            System.out.println(line);
        }
        return "hello, post method";
    }
}

3.2 客户端

新建一个客户端的项目。

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.4.1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.yqd</groupId>
    <artifactId>hello-rest-template</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <name>hello-rest-template</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.73</version>
        </dependency>
        <dependency>
            <groupId>com.squareup.okhttp3</groupId>
            <artifactId>okhttp</artifactId>
            <version>3.14.4</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

server:
  port: 8091

添加RestTemplate的配置类

@Configuration
public class RestTemplateConfig {
    @Bean
    public RestTemplate restTemplate(ClientHttpRequestFactory factory) {
        RestTemplate restTemplate = new RestTemplate(factory);
        // 支持中文编码
        restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(Charset.forName("UTF-8")));
        return restTemplate;
    }

    /**RestTemplate 支持至少三种HTTP客户端库：JDK自带的HttpURLConnection，Apache HttpComponents，OkHttp。
     * 从各种HTTP客户端性能以及易用程度评测来看，OkHttp 优于 Apache HttpComponents、Apache HttpComponents优于HttpURLConnection。
     * 所以我个人更建议大家将底层HTTP实现切换为okHTTP。
     */
    @Bean
    public ClientHttpRequestFactory myClientHttpRequestFactory() {
        OkHttp3ClientHttpRequestFactory factory= new OkHttp3ClientHttpRequestFactory(); //此处使用自定义的OkHttp客户端，需要引入okhttp依赖，已在pom中引入
        factory.setReadTimeout(2000);//从服务器获取数据超时时间 单位为ms
        factory.setConnectTimeout(2000);//连接超时时间 单位为ms
        return factory;
    }
}

4.客户端发送get请求

@Autowired
private RestTemplate restTemplate;

@Test
void getMethod() {
    String url = "http://localhost:8090/getData";
    //String result = restTemplate.getForObject(url, String.class); //直接返回响应内容
    ResponseEntity<String> responseEntity = restTemplate.getForEntity(url, String.class);//返回响应体
    System.out.println(responseEntity.getStatusCode()); //200 OK
    System.out.println(responseEntity.getStatusCodeValue()); 200
    System.out.println(responseEntity.getBody());//hello, get method
    System.out.println(responseEntity.getClass()); //class org.springframework.http.ResponseEntity
    System.out.println(responseEntity.getHeaders());//[Vary:"Origin", "Access-Control-Request-Method", "Access-Control-Request-Headers", Content-Type:"text/plain;charset=UTF-8", Content-Length:"17", Date:"Mon, 11 Jan 2021 12:04:14 GMT", Keep-Alive:"timeout=60", Connection:"keep-alive"]
}

5.客户端发送post请求

@Test
public void testPost() throws UnsupportedEncodingException {

    String url = "http://localhost:8090/postData";
    //1、header
    HttpHeaders header = new HttpHeaders();
    header.add("username", "tom");
    header.add("charset", "utf-8");
    header.add("Content-Type", "application/json");

    //2、body 有两种数据封装方式，第一种是使用MultiValueMap，第二种是直接用JSONObject发送json对象
    //        MultiValueMap<String, String> requestBody = new LinkedMultiValueMap<>();
    //        requestBody.add("data", "123456");
    JSONObject requestBody = new JSONObject();//放入body中的json参数
    requestBody.put("data", "123456");

    //3、把header和body封装到请求中
    HttpEntity<JSONObject> httpEntity = new HttpEntity<>(requestBody, header);

    //4、提交请求,得到响应
    //String response = restTemplate.postForObject(url, httpEntity, String.class); //直接返回响应内容
    ResponseEntity<String> responseEntity = restTemplate.postForEntity(url, httpEntity, String.class);//返回响应体
    System.out.println(responseEntity.toString()); //<200,hello, post method,[Vary:"Origin", "Access-Control-Request-Method", "Access-Control-Request-Headers", Content-Type:"text/plain;charset=UTF-8", Content-Length:"18", Date:"Mon, 11 Jan 2021 12:05:42 GMT", Keep-Alive:"timeout=60", Connection:"keep-alive"]>
}

6.使用exchange方法

只需要把getForEntity、postForEntity等方法换成exchange就可以了

@Test
public void testExchage() throws UnsupportedEncodingException {

    String url = "http://localhost:8090/postData";
    //1、header
    HttpHeaders header = new HttpHeaders();
    header.add("username", "tom");
    header.add("charset", "utf-8");
    header.add("Content-Type", "application/json");

    //2、body 有两种数据封装方式，第一种是使用MultiValueMap，第二种是直接用JSONObject发送json对象
    //        MultiValueMap<String, String> requestBody = new LinkedMultiValueMap<>();
    //        requestBody.add("data", "123456");
    JSONObject requestBody = new JSONObject();//放入body中的json参数
    requestBody.put("data", "123456");

    //3、把header和body封装到请求中
    HttpEntity<JSONObject> entity = new HttpEntity<JSONObject>(requestBody, header);

    //4、提交请求
    ResponseEntity<String> exchange = restTemplate.exchange(url, HttpMethod.POST, entity, String.class);
    System.out.println(exchange.toString());
}

7.如何自定义请求拦截器

7.1 增加CustomInterceptor类

public class CustomInterceptor implements ClientHttpRequestInterceptor {
    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
        HttpHeaders headers = request.getHeaders();
        // 加入自定义请求头
        headers.add("xy","1024" );
        System.out.println("通过请求拦截器查看请求头："+headers);
        // 请求继续被执行
        return execution.execute(request, body);
    }
}

7.2 在RestTemplate配置类中增加配置

RestTemplateConfig中增加如下拦截器配置。

@Bean
public RestTemplate restTemplate(ClientHttpRequestFactory factory) {
    RestTemplate restTemplate = new RestTemplate(factory);
    //配置自定义的请求拦截处理器
    restTemplate.setInterceptors(Arrays.asList(new CustomInterceptor()));
    // 支持中文编码
    restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(Charset.forName("UTF-8")));
    return restTemplate;
}

测试的时候会发现每次打印请求头信息，说明请求经过了拦截器。如果在请求时有其他需求，比如动态增加头部信息，校验头部信息等可以在拦截器中修改。

8.如何自定义请求异常处理

8.1 增加CustomErrorHandler类

public class CustomErrorHandler implements ResponseErrorHandler {

    private static final Logger LOGGER = LoggerFactory.getLogger(CustomErrorHandler.class);

    /**
     * 返回false表示不管response的status是多少都返回没有错
     * 这里可以自己定义那些status code你认为是可以抛Error
     */
    @Override
    public boolean hasError(ClientHttpResponse response) throws IOException {
        return response.getStatusCode().value() != 200 && response.getStatusCode().value() !=302;
    }

    /**
     * 这里面可以实现你自己遇到了Error进行合理的处理
     */
    @Override
    public void handleError(ClientHttpResponse response) throws IOException {
        System.out.println("请求中有错误");
    }

    /**
     * 重载方法
     */
    @Override
    public void handleError(URI url, HttpMethod method, ClientHttpResponse response) throws IOException {
        LOGGER.error("=======================ERROR============================");
        LOGGER.error("DateTime：{}", DateUtil.generateTimeFormatter(response.getHeaders().getDate(),"yyyy-MM-dd HH:mm:ss"));
        LOGGER.error("HOST:{},URI：{}", url.getHost(),url.getPath());
        LOGGER.error("Method：{}", method.name());
        LOGGER.error("Exception：{}", response.getStatusCode());
        LOGGER.error("========================================================");
    }
}

8.2 在RestTemplate配置类中增加配置

@Bean
public RestTemplate restTemplate(ClientHttpRequestFactory factory) {
    RestTemplate restTemplate = new RestTemplate(factory);
    //配置自定义的请求拦截处理器
    restTemplate.setInterceptors(Arrays.asList(new CustomInterceptor()));
    //配置自定义的请求异常处理器
    restTemplate.setErrorHandler(new CustomErrorHandler());
    // 支持中文编码
    restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(Charset.forName("UTF-8")));
    return restTemplate;
}

测试的时候，启动服务器，请求的url设置一个错误参数，可以看到错误信息，而不会报RestTemplate默认的异常。

默认异常：（后台报红）

org.springframework.web.client.HttpClientErrorException$NotFound: 404

配置之后的异常：（后台不会报红）

拦截器查看请求头：[Accept:"text/plain, application/json, application/*+json, */*", username:"tom", charset:"utf-8", Content-Type:"application/json", Content-Length:"17", xy:"1024"]
2021-01-14 19:05:24.024 ERROR 22768 --- [           main] com.yqd.config.CustomErrorHandler        : =======================ERROR============================
2021-01-14 19:05:24.025 ERROR 22768 --- [           main] com.yqd.config.CustomErrorHandler        : DateTime：2021-01-14 19:05:23
2021-01-14 19:05:24.025 ERROR 22768 --- [           main] com.yqd.config.CustomErrorHandler        : HOST:localhost,URI：/postData1
2021-01-14 19:05:24.025 ERROR 22768 --- [           main] com.yqd.config.CustomErrorHandler        : Method：POST
2021-01-14 19:05:24.025 ERROR 22768 --- [           main] com.yqd.config.CustomErrorHandler        : Exception：404 NOT_FOUND
2021-01-14 19:05:24.025 ERROR 22768 --- [           main] com.yqd.config.CustomErrorHandler        : ========================================================
HTTP 响应状态：404 NOT_FOUND
<404,{"timestamp":"2021-01-14T11:05:24.024+00:00","status":404,"error":"Not Found","message":"","path":"/postData1"},[Connection:"keep-alive", Content-Type:"application/json", Date:"Thu, 14 Jan 2021 11:05:23 GMT", Keep-Alive:"timeout=60", Transfer-Encoding:"chunked", Vary:"Origin", "Access-Control-Request-Method", "Access-Control-Request-Headers"]>