Springboot之访问web资源

在springmvc中，访问web资源是重要的知识。

其中springboot整合了主要两种访问web资源的方式。

RestTemplate访问

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（来源于极客时间丁雪丰老师课件）

以一个例子来说明访问方法：

1.restemplate 配置方式：

//一般采用builder模式进行构建和配置
//或者以构造器的方式进行构建@Beanpublic RestTemplate restTemplate(RestTemplateBuilder builder) {
//		return new RestTemplate();return builder.build();}

2.构建uri

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使用UriComponentBuilder类进行资源访问绑定，采用builder模式进行传参

URI uri = UriComponentsBuilder.fromUriString("http://localhost:8080/coffee/{id}").build(1);

3.确定资源访问方式：

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（来源于极客时间丁雪丰老师课件）

例如：

		//getForEntity()方法以get方式在指定的uri上查询资源并以entity——coffee类型访问实体listResponseEntity<Coffee> c = restTemplate.getForEntity(uri, Coffee.class);log.info("Response Status: {}, Response Headers: {}", c.getStatusCode(), c.getHeaders().toString());log.info("Coffee: {}", c.getBody());//以post方式去更新资源，则需要创建一个Coffee类对象，作为请求体传进去，同时//调用postForObject()方法来返回更新掉的资源类型String coffeeUri = "http://localhost:8080/coffee/";Coffee request = Coffee.builder().name("Americano").price(BigDecimal.valueOf(25.00)).build();Coffee response = restTemplate.postForObject(coffeeUri, request, Coffee.class);log.info("New Coffee: {}", response);String s = restTemplate.getForObject(coffeeUri, String.class);log.info("String: {}", s);

RestTemplate访问之升级版

传递 HTTP Header
• RestTemplate.exchange()
• RequestEntity / ResponseEntity

官网上对于这个的介绍是

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URI uri = UriComponentsBuilder.fromUriString("http://localhost:8080/coffee/?name={name}").build("mocha");
RequestEntity<Void> req = RequestEntity.get(uri).accept(MediaType.APPLICATION_XML).build();
ResponseEntity<String> resp = restTemplate.exchange(req, String.class);
log.info("Response Status: {}, Response Headers: {}",  resp.getStatusCode(),resp.getHeaders().toString());
log.info("Coffee: {}", resp.getBody());

类型转换
• JsonSerializer / JsonDeserializer
• @JsonComponent

解析泛型对象
• RestTemplate.exchange()
• ParameterizedTypeReference

在解析泛型对象时应借助ParameterizedTypeReference

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		String coffeeUri = "http://localhost:8080/coffee/";Coffee request = Coffee.builder().name("Americano").price(Money.of(CurrencyUnit.of("CNY"), 25.00)).build();Coffee response = restTemplate.postForObject(coffeeUri, request, Coffee.class);log.info("New Coffee: {}", response);ParameterizedTypeReference<List<Coffee>> ptr =new ParameterizedTypeReference<List<Coffee>>() {};ResponseEntity<List<Coffee>> list = restTemplate.exchange(coffeeUri, HttpMethod.GET, null, ptr);list.getBody().forEach(c -> log.info("Coffee: {}", c));

这里贴出restTemplate的exchange()方法的介绍

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定制化RestTemplate

默认是实现SipleClientHttpRequestFactory

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这方面的应用可以以下面的例子来说明

1.定义一个链接保持时间的策略类，主要是通过实现ConnectionKeepAliveStrategy接口

public class CustomConnectionKeepAliveStrategy implements ConnectionKeepAliveStrategy {private final long DEFAULT_SECONDS = 30;@Overridepublic long getKeepAliveDuration(HttpResponse response, HttpContext context) {return Arrays.asList(response.getHeaders(HTTP.CONN_KEEP_ALIVE)).stream().filter(h -> StringUtils.equalsIgnoreCase(h.getName(), "timeout")&& StringUtils.isNumeric(h.getValue())).findFirst().map(h -> NumberUtils.toLong(h.getValue(), DEFAULT_SECONDS)).orElse(DEFAULT_SECONDS) * 1000;}
}

2.创建一个requestFactory

	@Beanpublic HttpComponentsClientHttpRequestFactory requestFactory() {//先创建链接管理器对象，来设置最大链接个数PoolingHttpClientConnectionManager connectionManager =new PoolingHttpClientConnectionManager(30, TimeUnit.SECONDS);connectionManager.setMaxTotal(200);connectionManager.setDefaultMaxPerRoute(20);//创建可关闭的httpclientCloseableHttpClient httpClient = HttpClients.custom().setConnectionManager(connectionManager).evictIdleConnections(30, TimeUnit.SECONDS).disableAutomaticRetries()// 有 Keep-Alive 认里面的值，没有的话永久有效//.setKeepAliveStrategy(DefaultConnectionKeepAliveStrategy.INSTANCE)// 换成自定义的.setKeepAliveStrategy(new CustomConnectionKeepAliveStrategy()).build();//包装上这个属性HttpComponentsClientHttpRequestFactory requestFactory =new HttpComponentsClientHttpRequestFactory(httpClient);return requestFactory;}

4.调用的主要方法：

	@Overridepublic void run(ApplicationArguments args) throws Exception {URI uri = UriComponentsBuilder.fromUriString("http://localhost:8080/coffee/?name={name}").build("mocha");RequestEntity<Void> req = RequestEntity.get(uri).accept(MediaType.APPLICATION_XML).build();ResponseEntity<String> resp = restTemplate.exchange(req, String.class);log.info("Response Status: {}, Response Headers: {}", resp.getStatusCode(), resp.getHeaders().toString());log.info("Coffee: {}", resp.getBody());String coffeeUri = "http://localhost:8080/coffee/";Coffee request = Coffee.builder().name("Americano").price(Money.of(CurrencyUnit.of("CNY"), 25.00)).build();Coffee response = restTemplate.postForObject(coffeeUri, request, Coffee.class);log.info("New Coffee: {}", response);ParameterizedTypeReference<List<Coffee>> ptr =new ParameterizedTypeReference<List<Coffee>>() {};ResponseEntity<List<Coffee>> list = restTemplate.exchange(coffeeUri, HttpMethod.GET, null, ptr);list.getBody().forEach(c -> log.info("Coffee: {}", c));}

izedTypeReference<List>() {};
ResponseEntity<List> list = restTemplate
.exchange(coffeeUri, HttpMethod.GET, null, ptr);
list.getBody().forEach(c -> log.info(“Coffee: {}”, c));
}