RestTemplate的应用

砒霜拌辣椒

发布于 2023-08-23 17:24:41

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文章被收录于专栏：HerculesHercules

Spring提供了一种简单便捷的模板类 RestTemplate 来调用 RESTful 接口。它提供了多种便捷访问HTTP服务的方法，能够大大提高客户端的编写效率。

RestTemplate方法	HTTP方法
getForEntity	GET
getForObject	GET
postForEntity	POST
postForObject	POST
put	PUT
patch	PATCH
delete	DELETE
exchange	any
execute	any

1、RESTful API接口

@RestController
@Slf4j
public class RestfulController {
    @GetMapping(value = "/getUser1", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public User getUser1() {
        return new User(1L, "zhaoxb");
    }

    @GetMapping(value = "/getUser2", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public User getUser2(User user) {
        log.info("getUser2:{}", JSONUtil.toJsonPrettyStr(user));
        return user;
    }

    @PostMapping(value = "/postUser", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public User postUser(User user) {
        log.info("postUser:{}", JSONUtil.toJsonPrettyStr(user));
        return user;
    }
    
    @PostMapping(value = "/postBody", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public User postBody(@RequestBody User user) {
        log.info("postBody:{}", JSONUtil.toJsonPrettyStr(user));
        return user;
    }
}

GET请求，不带参。
GET请求，带参。
POST请求，带参。
POST请求，带有请求体。

实体类，需要提供有参和无参构造

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Long id;
    private String name;
}

RestTemplate配置类

@Configuration
public class RestConfig {
    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder restTemplateBuilder) {
        RestTemplate restTemplate = restTemplateBuilder
                .setConnectTimeout(Duration.ofMillis(5000L))
                .setReadTimeout(Duration.ofMillis(30000L))
                .build();
        return restTemplate;
    }
}

2、发送GET请求

2.1、getForEntity方法，不带参

@ActiveProfiles("test")
@RunWith(SpringRunner.class)
@SpringBootTest
@Slf4j
public class RestfulGetTests {
    @Autowired
    private RestTemplate restTemplate;

    @Test
    public void getForEntity1() {
        ResponseEntity<String> responseEntity = restTemplate.getForEntity("http://127.0.0.1:31000/getUser1", String.class);
        log.info("响应码:{}", responseEntity.getStatusCodeValue());
        log.info("响应体:{}", JSONUtil.toJsonPrettyStr(responseEntity.getBody()));
    }
}

响应码:200
响应体:{
    "name": "zhaoxb",
    "id": 1
}

2.2、getForEntity方法，数字占位符方式传参

@Test
public void getForEntity2() {
    ResponseEntity<String> responseEntity = restTemplate.getForEntity("http://127.0.0.1:31000/getUser2?id={1}&name={2}", String.class, 2, "zhaoxb");
    log.info("响应体:{}", JSONUtil.toJsonPrettyStr(responseEntity.getBody()));
}

用一个数字做占位符。最后是一个可变长度的参数，用来替换前面的占位符。

响应体:{
    "name": "zhaoxb",
    "id": 2
}

2.3、getForEntity方法，map占位符方式传参

@Test
public void getForEntity3() {
    Map<String, Object> map = new HashMap<>();
    map.put("id", 3);
    map.put("name", "zhaoxb");
    ResponseEntity<String> responseEntity = restTemplate.getForEntity("http://127.0.0.1:31000/getUser2?id={id}&name={name}", String.class, map);
    log.info("响应体:{}", JSONUtil.toJsonPrettyStr(responseEntity.getBody()));
}

使用 name={name} 这种形式。最后一个参数是map，map的key为前边占位符的名字，value为实际参数值。

响应体:{
    "name": "zhaoxb",
    "id": 3
}

2.4、getForEntity方法，返回对象

@Test
public void getForEntity4() {
    ResponseEntity<User> responseEntity = restTemplate.getForEntity("http://127.0.0.1:31000/getUser1", User.class);
    log.info("响应体:{}", JSONUtil.toJsonPrettyStr(responseEntity.getBody()));
}

响应体:{
    "name": "zhaoxb",
    "id": 1
}

2.5、getForObject方法，直接返回对象

@Test
public void getForObject() {
    User User = restTemplate.getForObject("http://127.0.0.1:31000/getUser1", User.class);
    log.info("响应体:{}", JSONUtil.toJsonPrettyStr(User));
}

getForObject是对getForEntity函数的进一步封装，只关注返回消息的实体内容。

响应体:{
    "name": "zhaoxb",
    "id": 1
}

3、发送POST请求

用post方法发送带参的请求时，Map不能被定义为 HashMap、LinkedHashMap，而应被定义为 LinkedMultiValueMap，这样参数才能成功传递到后台。

3.1、postForEntity方法

@Test
public void postForEntity() {
    MultiValueMap<String, Object> multiValueMap = new LinkedMultiValueMap<>();
    multiValueMap.add("id", 5);
    multiValueMap.add("name", "zhaoxb");
    ResponseEntity<User> responseEntity = restTemplate.postForEntity("http://127.0.0.1:31000/postUser", multiValueMap, User.class);
    log.info("响应码:{}", responseEntity.getStatusCodeValue());
    log.info("响应体:{}", JSONUtil.toJsonPrettyStr(responseEntity.getBody()));
}

响应体:{
    "name": "zhaoxb",
    "id": 5
}

3.2、postForObject方法

@Test
public void postForObject() {
    MultiValueMap<String, Object> multiValueMap = new LinkedMultiValueMap<>();
    multiValueMap.add("id", 6);
    multiValueMap.add("name", "zhaoxb");
    User user = restTemplate.postForObject("http://127.0.0.1:31000/postUser", multiValueMap, User.class);
    log.info("响应体:{}", JSONUtil.toJsonPrettyStr(user));
}

和 getForObject 相对应，只关注返回的消息体。

响应体:{
    "name": "zhaoxb",
    "id": 6
}

3.3、postForObject方法，带有请求体body

@Test
public void postForObject2() {
    User reqUser = new User(10L, "zhaoxb");
    User user = restTemplate.postForObject("http://127.0.0.1:31000/postBody", reqUser, User.class);
    log.info("响应体:{}", JSONUtil.toJsonPrettyStr(user));
}

RestTemplate底层实现序列化和反序列化。

响应体:{
    "name": "zhaoxb",
    "id": 10
}

3.4、exchange方法

@Test
public void exchange() {
    MultiValueMap<String, Object> multiValueMap = new LinkedMultiValueMap<>();
    multiValueMap.add("id", 7);
    multiValueMap.add("name", "zhaoxb");
    HttpEntity<MultiValueMap<String, Object>> httpEntity = new HttpEntity<>(multiValueMap);
//      HttpEntity<MultiValueMap<String, Object>> httpEntityWithHeaders = new HttpEntity<>(multiValueMap, new HttpHeaders());
    ResponseEntity<User> responseEntity = restTemplate.exchange("http://127.0.0.1:31000/postUser", HttpMethod.POST, httpEntity, User.class);
    log.info("响应体:{}", JSONUtil.toJsonPrettyStr(responseEntity.getBody()));
}

HttpEntity还支持带有HTTP请求头的构造方法。

响应体:{
    "name": "zhaoxb",
    "id": 7
}

用RestTemplate发送PUT、PATCH、DELETE方法与GET、POST方法非常类似，这里不做展开。

4、自定义template

4.1、自定义HTTP源

ClientHttpRequestFactory是Spring定义的一个接口，用于生产ClientHttpRequest对象，RestTemplate只是模板类，抽象了很多调用方法，而底层真正使用何种框架发送HTTP请求是通过ClientHttpRequestFactory指定的。

RestTemplate默认使用的是SimpleClientHttpRequestFactory，其内部使用的是JDK的java.net.HttpURLConnection创建底层连接，默认是没有连接池的。可以通过 setRequestFactory 函数设置不同的HTTP源，比如 Apache HttpComponents、Netty和OkHttp。

设置Apache HttpComponents为HTTP客户端源

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

@Configuration
public class RestConfig {
    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder restTemplateBuilder) {
        RestTemplate restTemplate = restTemplateBuilder
                .setConnectTimeout(Duration.ofMillis(5000L))
                .setReadTimeout(Duration.ofMillis(30000L))
                .requestFactory(() -> clientHttpRequestFactory())
                .build();
        return restTemplate;
    }

    @Bean
    public ClientHttpRequestFactory clientHttpRequestFactory() {
        HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();

        //开始设置连接池
        PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager();
        poolingHttpClientConnectionManager.setMaxTotal(100);  //最大连接数
        poolingHttpClientConnectionManager.setDefaultMaxPerRoute(20);  //同路由并发数
        httpClientBuilder.setConnectionManager(poolingHttpClientConnectionManager);

        HttpClient httpClient = httpClientBuilder.build();
        // httpClient连接配置
        HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);
        // 设置超时，如果 RestTemplateBuilder 已经设置，这里就不需要设置
//        clientHttpRequestFactory.setConnectTimeout(5 * 1000); // 连接超时
//        clientHttpRequestFactory.setReadTimeout(30 * 1000); // 数据读取超时时间
        clientHttpRequestFactory.setConnectionRequestTimeout(30 * 1000); //连接不够用的等待时间
        return clientHttpRequestFactory;
    }
}