【WEB系列】RestTemplate基础用法小结

文章目录

1. I. 项目搭建
   1. 1. 配置
   2. 2. Rest服务
2. II. RestTemplate示例
   1. 1. Get请求
   2. 2. POST表单
   3. 3. post body
   4. 4. 小结
3. II. 其他
   1. 0. 项目
   2. 1. 一灰灰Blog

在Spring项目中，通常会借助RestTemplate来实现网络请求，RestTemplate封装得很完善了，基本上可以非常简单的完成各种HTTP请求，本文主要介绍一下基本操作，最常见的GET/POST请求的使用姿势

I. 项目搭建

1. 配置

借助SpringBoot搭建一个SpringWEB项目，提供一些用于测试的REST服务

• SpringBoot版本: 2.2.1.RELEASE
• 核心依赖: spring-boot-stater-web

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

为了后续输出的日志更直观，这里设置了一下日志输出格式，在配置文件application.yml中，添加

logging:
  pattern:
    console: (%msg%n%n){blue}

2. Rest服务

添加三个接口，分别提供GET请求，POST表单，POST json对象，然后返回请求头、请求参数、cookie，具体实现逻辑相对简单，也不属于本篇重点，因此不赘述说明

@RestController
public class DemoRest {


    private String getHeaders(HttpServletRequest request) {
        Enumeration<String> headerNames = request.getHeaderNames();
        String name;

        JSONObject headers = new JSONObject();
        while (headerNames.hasMoreElements()) {
            name = headerNames.nextElement();
            headers.put(name, request.getHeader(name));
        }
        return headers.toJSONString();
    }

    private String getParams(HttpServletRequest request) {
        return JSONObject.toJSONString(request.getParameterMap());
    }

    private String getCookies(HttpServletRequest request) {
        Cookie[] cookies = request.getCookies();
        if (cookies == null || cookies.length == 0) {
            return "";
        }

        JSONObject ck = new JSONObject();
        for (Cookie cookie : cookies) {
            ck.put(cookie.getName(), cookie.getValue());
        }
        return ck.toJSONString();
    }

    private String buildResult(HttpServletRequest request) {
        return buildResult(request, null);
    }

    private String buildResult(HttpServletRequest request, Object obj) {
        String params = getParams(request);
        String headers = getHeaders(request);
        String cookies = getCookies(request);

        if (obj != null) {
            params += " | " + obj;
        }

        return "params: " + params + "\nheaders: " + headers + "\ncookies: " + cookies;
    }

    @GetMapping(path = "get")
    public String get(HttpServletRequest request) {
        return buildResult(request);
    }


    @PostMapping(path = "post")
    public String post(HttpServletRequest request) {
        return buildResult(request);
    }

    @Data
    @NoArgsConstructor
    public static class ReqBody implements Serializable {
        private static final long serialVersionUID = -4536744669004135021L;
        private String name;
        private Integer age;
    }

    @PostMapping(path = "body")
    public String postBody(@RequestBody ReqBody body) {
        HttpServletRequest request =
                ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
        return buildResult(request, body);
    }
}

II. RestTemplate示例

1. Get请求

使用RestTemplate发起GET请求，通常有两种常见的方式

• getForEntity: 返回的正文对象包装在HttpEntity实体中，适用于获取除了返回的正文之外，对返回头、状态码有需求的场景
• getForObject: 返回正文，适用于只对正文感兴趣的场景

上面这两种方法除了返回结果不同之外，其他的使用姿势基本一样，有三种

@Nullable
public <T> T getForObject(String url, Class<T> responseType, Object... uriVariables) throws RestClientException;

@Nullable
public <T> T getForObject(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;

@Nullable
public <T> T getForObject(URI url, Class<T> responseType) throws RestClientException;

上面三个重载方法，区别仅在于GET参数如何处理，下面给出一个实例进行说明

/**
 * 基本的get请求
 */
public void basicGet() {
    RestTemplate restTemplate = new RestTemplate();

    HttpEntity<String> res =
            restTemplate.getForEntity("http://127.0.0.1:8080/get?name=一灰灰Blog&age=20", String.class);
    res.get
    log.info("Simple getForEntity res: {}", res);

    // 直接在url中拼参数，调用的是前面对应的方法1; 当然这里也可以将url转成URI格式，这样调用的是方法3
    String response = restTemplate.getForObject("http://127.0.0.1:8080/get?name=一灰灰Blog&age=20", String.class);
    log.info("Simple getForObject res: {}", response);

    // 通过可变参数，填充url参数中的{?}, 注意顺序是对应的
    response = restTemplate.getForObject("http://127.0.0.1:8080/get?name={?}&age={?}", String.class, "一灰灰Blog", 20);
    log.info("Simple getForObject by uri params: {}", response);

    // 参数放在map中，通过map的key与url中的{}进行匹配，实现参数替换
    response = restTemplate.getForObject("http://127.0.0.1:8080/get?name={name}&age={age}", String.class,
            new HashMap<String, Object>() {
                {
                    put("name", "一灰灰Blog");
                    put("age", 20);
                }
            });
    log.info("Simple getForObject by uri map params: {}", response);
}

输出结果如下:

(Simple getForEntity res: <200,params: {"name":["一灰灰Blog"],"age":["20"]}
headers: {"host":"127.0.0.1:8080","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies: ,[Content-Type:"text/plain;charset=UTF-8", Content-Length:"213", Date:"Wed, 17 Jun 2020 01:14:16 GMT"]>

(Simple getForObject res: params: {"name":["一灰灰Blog"],"age":["20"]}
headers: {"host":"127.0.0.1:8080","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies: 

(Simple getForObject by uri params: params: {"name":["一灰灰Blog"],"age":["20"]}
headers: {"host":"127.0.0.1:8080","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies: 

(Simple getForObject by uri map params: params: {"name":["一灰灰Blog"],"age":["20"]}
headers: {"host":"127.0.0.1:8080","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies:

2. POST表单

POST表单属于非常基础的请求方式了，根据返回结果，RestTemplate同样提供了两种姿势

• postForEntity: 返回的正文封装在HttpEntity
• postForObject: 直接返回正文对象

它的使用姿势一样有三种

@Nullable
public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Object... uriVariables);

@Nullable
public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Map<String, ?> uriVariables);

@Nullable
public <T> T postForObject(URI url, @Nullable Object request, Class<T> responseType);

请注意上面三个方法的前两个，后面的uriVariables是url参数，不是POST表单参数哦，它们之间是有区别的（虽然我们一般post提交表单时，不怎么会在url中添加参数）

下面还是根据实际的用例来查看

/**
 * post基本请求
 */
public void basicPost() {
    RestTemplate restTemplate = new RestTemplate();

    HttpEntity<String> res = restTemplate
            .postForEntity("http://127.0.0.1:8080/post?name=一灰灰Blog&age=20", new LinkedMultiValueMap<>(),
                    String.class);
    log.info("Simple postForEntity res: {}", res);

    // 提交的表单参数
    MultiValueMap<String, Object> params = new LinkedMultiValueMap<>();
    params.add("name", "一灰灰Blog");
    params.add("age", 20);

    String response = restTemplate.postForObject("http://127.0.0.1:8080/post", params, String.class);
    log.info("Simple postForObject res: {}", response);

    // 这个url参数是放在url上面的哦
    response = restTemplate.postForObject("http://127.0.0.1:8080/post?urlName={?}", params, String.class, "url参数");
    log.info("Simple postForObject with urlParams res: {}", response);

    response = restTemplate.postForObject("http://127.0.0.1:8080/post?urlName={urlName}", params, String.class,
            new HashMap<String, Object>() {{
                put("urlName", "url参数");
            }});
    log.info("Simple postForObject with map urlParams res: {}", response);
}

测试输出如下

(Simple postForEntity res: <200,params: {"name":["一灰灰Blog"],"age":["20"]}
headers: {"content-length":"0","host":"127.0.0.1:8080","content-type":"application/x-www-form-urlencoded;charset=UTF-8","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies: ,[Content-Type:"text/plain;charset=UTF-8", Content-Length:"299", Date:"Wed, 17 Jun 2020 01:14:16 GMT"]>

(Simple postForObject res: params: {"name":["一灰灰Blog"],"age":["20"]}
headers: {"content-length":"338","host":"127.0.0.1:8080","content-type":"multipart/form-data;charset=UTF-8;boundary=URAN0wQz_s1vauFbDLFRZ40bb3NtRRwgLuII-wCk","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies: 

(Simple postForObject with urlParams res: params: {"name":["一灰灰Blog"],"age":["20"],"urlName":["url参数"]}
headers: {"content-length":"314","host":"127.0.0.1:8080","content-type":"multipart/form-data;charset=UTF-8;boundary=2h15swz9SJPfjCxv2cNOwDn_TR2nK4gF","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies: 

(Simple postForObject with map urlParams res: params: {"name":["一灰灰Blog"],"age":["20"],"urlName":["url参数"]}
headers: {"content-length":"329","host":"127.0.0.1:8080","content-type":"multipart/form-data;charset=UTF-8;boundary=QOhroKp7BE4cNF5Oi3CJLdq_ixzk0t5ZZw9ch","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies:

3. post body

post一个json串，也属于比较常见的一种case了，对于RestTemplate而言，要支持这种方式，需要额外处理一下请求头，设置Content-Type为application/json

使用姿势和上面相差不大，只是需要注意一下请求参数的构建

/**
 * json表单
 */
public void jsonPost() {
    RestTemplate restTemplate = new RestTemplate();

    // 设置请求头
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON);

    // 提交的json串
    JSONObject params = new JSONObject();
    params.put("name", "一灰灰Blog");
    params.put("age", 20);

    // 构建请求参数
    HttpEntity<String> request = new HttpEntity<>(params.toJSONString(), headers);

    String response = restTemplate.postForObject("http://127.0.0.1:8080/body", request, String.class);
    log.info("json post res: {}", response);
}

输出如下

(json post res: params: {} | DemoRest.ReqBody(name=???Blog, age=20)
headers: {"content-length":"27","host":"127.0.0.1:8080","content-type":"application/json","connection":"keep-alive","accept":"text/plain, application/json, application/*+json, */*","user-agent":"Java/1.8.0_171"}
cookies:

请注意，提交的json串中文乱码了

4. 小结

上面主要介绍的是RestTemplate的常规用法，基础的GET/POST请求姿势，如果业务简单，不需要考虑各种复杂的异常情况，也是没有太多的问题了；那么如果需要考虑，又有哪些需要注意的呢？

• 上面的中文乱码问题如何解决？
• 自定义的请求头如何塞入（如果是爬虫，上面的User-Agent太容易被屏蔽了）
• cookie设置
• REST支持Basic Auth的验证方式如何发起请求
• 超时设置
• 自定义连接池替换
• REST返回非200状态码的情况，能否不抛异常，自定义处理？
• ssl校验
• …

如果你对上面的这些点感兴趣，不妨关注一波，相关的文章快正热火朝天的进行中…

II. 其他

0. 项目

• 工程：https://github.com/liuyueyi/spring-boot-demo
• 项目: https://github.com/liuyueyi/spring-boot-demo/tree/master/spring-boot/221-web-resttemplate

1. 一灰灰Blog

尽信书则不如，以上内容，纯属一家之言，因个人能力有限，难免有疏漏和错误之处，如发现bug或者有更好的建议，欢迎批评指正，不吝感激

下面一灰灰的个人博客，记录所有学习和工作中的博文，欢迎大家前去逛逛

• 一灰灰Blog个人博客 https://blog.hhui.top
• 一灰灰Blog-Spring专题博客 http://spring.hhui.top

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