RestTemplate详解

程序员文章站 2022-04-28 17:29:33

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概述

当我们在开发项目的过程中，一个系统中要请求另外一个服务中的接口，那么通常是用过http请求，需要有个httpClient类：类似代码如下：

import com.alibaba.fastjson.JSONObject;
/**
 * HttpClient4.3工具类
 * @author tech
 * @date 2016-03-29
 *
 */
public class HttpClientUtils {
    private static Logger logger = LoggerFactory.getLogger(HttpClientUtils.class);    //日志记录
 
    /**
     * httpPost
     * @param url  路径
     * @param jsonParam 参数
     * @return
     */
    public static JSONObject httpPost(String url,JSONObject jsonParam){
        return httpPost(url, jsonParam, false);
    }
 
    /**
     * post请求
     * @param url         url地址
     * @param jsonParam     参数
     * @param noNeedResponse    不需要返回结果
     * @return
     */
    public static JSONObject httpPost(String url,JSONObject jsonParam, boolean noNeedResponse){
        //post请求返回结果
        CloseableHttpClient httpClient = HttpClients.createDefault();  
        JSONObject jsonResult = null;
        HttpPost httpPost = new HttpPost(url);
        //设置请求和传输超时时间
        RequestConfig requestConfig = RequestConfig.custom().setSocketTimeout(2000).setConnectTimeout(2000).build();
        httpPost.setConfig(requestConfig); 
        try {
            if (null != jsonParam) {
                //解决中文乱码问题
                StringEntity entity = new StringEntity(jsonParam.toString(), "utf-8");
                entity.setContentEncoding("UTF-8");
                entity.setContentType("application/json");
                httpPost.setEntity(entity);
            }
            CloseableHttpResponse result = httpClient.execute(httpPost);
            /**请求发送成功，并得到响应**/
            if (result.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                String str = "";
                try {
                    /**读取服务器返回过来的json字符串数据**/
                    str = EntityUtils.toString(result.getEntity(), "utf-8");
                    if (noNeedResponse) {
                        return null;
                    }
                    /**把json字符串转换成json对象**/
                    jsonResult = JSONObject.parseObject(str);
                } catch (Exception e) {
                    logger.error("post请求提交失败:" + url, e);
                }
            }
        } catch (IOException e) {
            logger.error("post请求提交失败:" + url, e);
        } finally{
        	httpPost.releaseConnection();
        }
        return jsonResult;
    }
 
 
    /**
     * 发送get请求
     * @param url    路径
     * @return
     */
    public static JSONObject httpGet(String url){
        //get请求返回结果
        JSONObject jsonResult = null;
        CloseableHttpClient client = HttpClients.createDefault();  
        //发送get请求
        HttpGet request = new HttpGet(url);
        //设置请求和传输超时时间
        RequestConfig requestConfig = RequestConfig.custom().setSocketTimeout(2000).setConnectTimeout(2000).build();
        request.setConfig(requestConfig); 
        try {
            CloseableHttpResponse response = client.execute(request);     
 
            /**请求发送成功，并得到响应**/
            if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                /**读取服务器返回过来的json字符串数据**/
            	HttpEntity entity = response.getEntity();
                String strResult = EntityUtils.toString(entity, "utf-8");
                /**把json字符串转换成json对象**/
                jsonResult = JSONObject.parseObject(strResult);
            } else {
                logger.error("get请求提交失败:" + url);
            }
        } catch (IOException e) {
            logger.error("get请求提交失败:" + url, e);
        } finally{
        	request.releaseConnection();
        }
        return jsonResult;
    }
}

今天讲一下spring中另外一种请求方式，通过RestTemplate 这个模板类：

RestTemplate与httpClient类似，都是java中可以模拟http请求的封装。但是RestTemplate比httpClient更优雅，它是spring中的一个封装功能。

RestTemplate也是java中的模板类。采用的设计模式中的模板模式。

源码解析

RestTemplate继承InterceptingHttpAccessor抽象类，实现RestOperation接口。

public class RestTemplate extends InterceptingHttpAccessor implements RestOperations

在RestOperations定义了基本的Rest操作集合。RestTemplate实现了这个接口。

public interface RestOperations {
 
	// GET
 
	<T> T getForObject(String url, Class<T> responseType, Object... uriVariables) throws RestClientException;
 
	<T> T getForObject(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;
 
	<T> T getForObject(URI url, Class<T> responseType) throws RestClientException;
 
	<T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... uriVariables) throws RestClientException;
 
	<T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;
 
	<T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType) throws RestClientException;
 
 
	// HEAD
 
	HttpHeaders headForHeaders(String url, Object... uriVariables) throws RestClientException;
 
	HttpHeaders headForHeaders(String url, Map<String, ?> uriVariables) throws RestClientException;
 
	HttpHeaders headForHeaders(URI url) throws RestClientException;
 
 
	// POST
 
	URI postForLocation(String url, Object request, Object... uriVariables) throws RestClientException;
 
	URI postForLocation(String url, Object request, Map<String, ?> uriVariables) throws RestClientException;
 
	URI postForLocation(URI url, Object request) throws RestClientException;
 
	<T> T postForObject(String url, Object request, Class<T> responseType, Object... uriVariables)
			throws RestClientException;
 
	<T> T postForObject(String url, Object request, Class<T> responseType, Map<String, ?> uriVariables)
			throws RestClientException;
 
	<T> T postForObject(URI url, Object request, Class<T> responseType) throws RestClientException;
 
	<T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Object... uriVariables)
			throws RestClientException;
 
	<T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Map<String, ?> uriVariables)
			throws RestClientException;
 
	<T> ResponseEntity<T> postForEntity(URI url, Object request, Class<T> responseType) throws RestClientException;
 
 
	// PUT
 
	void put(String url, Object request, Object... uriVariables) throws RestClientException;
 
	void put(String url, Object request, Map<String, ?> uriVariables) throws RestClientException;
 
	void put(URI url, Object request) throws RestClientException;
 
 
	// PATCH
 
	<T> T patchForObject(String url, Object request, Class<T> responseType, Object... uriVariables)
			throws RestClientException;
 
	<T> T patchForObject(String url, Object request, Class<T> responseType, Map<String, ?> uriVariables)
			throws RestClientException;
 
	<T> T patchForObject(URI url, Object request, Class<T> responseType) throws RestClientException;
 
 
 
	// DELETE
 
	void delete(String url, Object... uriVariables) throws RestClientException;
 
	void delete(String url, Map<String, ?> uriVariables) throws RestClientException;
 
	void delete(URI url) throws RestClientException;
 
 
	// OPTIONS
 
	Set<HttpMethod> optionsForAllow(String url, Object... uriVariables) throws RestClientException;
 
	Set<HttpMethod> optionsForAllow(String url, Map<String, ?> uriVariables) throws RestClientException;
 
	Set<HttpMethod> optionsForAllow(URI url) throws RestClientException;
 
 
	// exchange
 
	<T> ResponseEntity<T> exchange(String url, HttpMethod method, HttpEntity<?> requestEntity,
			Class<T> responseType, Object... uriVariables) throws RestClientException;
 
	<T> ResponseEntity<T> exchange(String url, HttpMethod method, HttpEntity<?> requestEntity,
			Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;
 
	<T> ResponseEntity<T> exchange(URI url, HttpMethod method, HttpEntity<?> requestEntity,
			Class<T> responseType) throws RestClientException;
 
	<T> ResponseEntity<T> exchange(String url,HttpMethod method, HttpEntity<?> requestEntity,
			ParameterizedTypeReference<T> responseType, Object... uriVariables) throws RestClientException;
 
	<T> ResponseEntity<T> exchange(String url, HttpMethod method, HttpEntity<?> requestEntity,
			ParameterizedTypeReference<T> responseType, Map<String, ?> uriVariables) throws RestClientException;
 
	<T> ResponseEntity<T> exchange(URI url, HttpMethod method, HttpEntity<?> requestEntity,
			ParameterizedTypeReference<T> responseType) throws RestClientException;
 
	<T> ResponseEntity<T> exchange(RequestEntity<?> requestEntity, Class<T> responseType) throws RestClientException;
 
	<T> ResponseEntity<T> exchange(RequestEntity<?> requestEntity, ParameterizedTypeReference<T> responseType)
			throws RestClientException;
 
 
	// general execution
 
	<T> T execute(String url, HttpMethod method, RequestCallback requestCallback,
			ResponseExtractor<T> responseExtractor, Object... uriVariables) throws RestClientException;
 
	<T> T execute(String url, HttpMethod method, RequestCallback requestCallback,
			ResponseExtractor<T> responseExtractor, Map<String, ?> uriVariables) throws RestClientException;
 
	<T> T execute(URI url, HttpMethod method, RequestCallback requestCallback,
			ResponseExtractor<T> responseExtractor) throws RestClientException;
 
}

PostForObject与PostForEntity的区别在于前者请求返回就是响应体，后者返回的是响应行，响应头，响应体。

这里也有一个基础的http访问类HttpAccessor,里面主要是一个工厂方法，用来构造HttpRequestFactory。

public abstract class HttpAccessor {
 
	protected final Log logger = LogFactory.getLog(getClass());
 
	private ClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
 
	public void setRequestFactory(ClientHttpRequestFactory requestFactory) {
		Assert.notNull(requestFactory, "ClientHttpRequestFactory must not be null");
		this.requestFactory = requestFactory;
	}
 
	public ClientHttpRequestFactory getRequestFactory() {
		return this.requestFactory;
	}
 
	protected ClientHttpRequest createRequest(URI url, HttpMethod method) throws IOException {
		ClientHttpRequest request = getRequestFactory().createRequest(url, method);
		if (logger.isDebugEnabled()) {
			logger.debug("Created " + method.name() + " request for \"" + url + "\"");
		}
		return request;
	}
 
}

springboot对RestTemplate的集成

1.首先添加配置

@Configuration
public class RestTemplateConfig {
	
	@Bean
	public RestTemplate restTemplate(){
		RestTemplate restTemplate = new RestTemplate();
		restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(StandardCharsets.UTF_8));
		return restTemplate;
	}
 
}

不然在service中的autowired会注入不进去

2.再设置请求头

		HttpHeaders headers = new HttpHeaders();
		headers.setContentType(MediaType.APPLICATION_JSON);

3.请求行，请求头，请求体分装成一个Entity

HttpEntity<String> entity = new HttpEntity<>(JSONObject.toJSONString(dto),headers );

4.接下来就调用
ResponseEntity r = restTemplate.exchange(ADD_URL, HttpMethod.POST, entity, String.class);

那就可以请求到结果了。

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