Spring提供的用于访问Rest服务的客户端：RestTemplate实践
Posted 沧海一滴
tags:
篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了Spring提供的用于访问Rest服务的客户端：RestTemplate实践相关的知识，希望对你有一定的参考价值。
什么是RestTemplate？
RestTemplate是Spring提供的用于访问Rest服务的客户端，RestTemplate提供了多种便捷访问远程Http服务的方法，能够大大提高客户端的编写效率。
调用RestTemplate的默认构造函数，RestTemplate对象在底层通过使用java.net包下的实现创建HTTP 请求，可以通过使用ClientHttpRequestFactory指定不同的HTTP请求方式。
ClientHttpRequestFactory接口主要提供了两种实现方式
- 一种是SimpleClientHttpRequestFactory，使用J2SE提供的方式（既java.net包提供的方式）创建底层的Http请求连接。
- 一种方式是使用HttpComponentsClientHttpRequestFactory方式，底层使用HttpClient访问远程的Http服务，使用HttpClient可以配置连接池和证书等信息。
xml配置的方式
请查看RestTemplate源码了解细节，知其然知其所以然！
RestTemplate默认是使用SimpleClientHttpRequestFactory，内部是调用jdk的HttpConnection，默认超时为-1
@Autowired
RestTemplate simpleRestTemplate
@Autowired
RestTemplate restTemplate
基于jdk的spring的RestTemplate
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"
default-autowire="byName" default-lazy-init="true">
<!--方式一、使用jdk的实现-->
<bean id="ky.requestFactory" class="org.springframework.http.client.SimpleClientHttpRequestFactory">
<property name="readTimeout" value="10000"/>
<property name="connectTimeout" value="5000"/>
</bean>
<bean id="simpleRestTemplate" class="org.springframework.web.client.RestTemplate">
<constructor-arg ref="ky.requestFactory"/>
<property name="messageConverters">
<list>
<bean class="org.springframework.http.converter.FormHttpMessageConverter"/>
<bean class="org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter"/>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter"/>
<bean class="org.springframework.http.converter.StringHttpMessageConverter">
<property name="supportedMediaTypes">
<list>
<value>text/plain;charset=UTF-8</value>
</list>
</property>
</bean>
</list>
</property>
</bean>
</beans>
使用Httpclient连接池的方式
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"
default-autowire="byName" default-lazy-init="true">
<!--方式二、使用httpclient的实现，带连接池-->
<bean id="ky.pollingConnectionManager" class="org.apache.http.impl.conn.PoolingHttpClientConnectionManager">
<!--整个连接池的并发-->
<property name="maxTotal" value="1000" />
<!--每个主机的并发-->
<property name="defaultMaxPerRoute" value="1000" />
</bean>
<bean id="ky.httpClientBuilder" class="org.apache.http.impl.client.HttpClientBuilder" factory-method="create">
<property name="connectionManager" ref="ky.pollingConnectionManager" />
<!--开启重试-->
<property name="retryHandler">
<bean class="org.apache.http.impl.client.DefaultHttpRequestRetryHandler">
<constructor-arg value="2"/>
<constructor-arg value="true"/>
</bean>
</property>
<property name="defaultHeaders">
<list>
<bean class="org.apache.http.message.BasicHeader">
<constructor-arg value="User-Agent"/>
<constructor-arg value="Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (Khtml, like Gecko) Chrome/31.0.1650.16 Safari/537.36"/>
</bean>
<bean class="org.apache.http.message.BasicHeader">
<constructor-arg value="Accept-Encoding"/>
<constructor-arg value="gzip,deflate"/>
</bean>
<bean class="org.apache.http.message.BasicHeader">
<constructor-arg value="Accept-Language"/>
<constructor-arg value="zh-CN"/>
</bean>
</list>
</property>
</bean>
<bean id="ky.httpClient" factory-bean="ky.httpClientBuilder" factory-method="build" />
<bean id="ky.clientHttpRequestFactory" class="org.springframework.http.client.HttpComponentsClientHttpRequestFactory">
<constructor-arg ref="ky.httpClient"/>
<!--连接超时时间，毫秒-->
<property name="connectTimeout" value="5000"/>
<!--读写超时时间，毫秒-->
<property name="readTimeout" value="10000"/>
</bean>
<bean id="restTemplate" class="org.springframework.web.client.RestTemplate">
<constructor-arg ref="ky.clientHttpRequestFactory"/>
<property name="errorHandler">
<bean class="org.springframework.web.client.DefaultResponseErrorHandler"/>
</property>
<property name="messageConverters">
<list>
<bean class="org.springframework.http.converter.FormHttpMessageConverter"/>
<bean class="org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter"/>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter"/>
<bean class="org.springframework.http.converter.StringHttpMessageConverter">
<property name="supportedMediaTypes">
<list>
<value>text/plain;charset=UTF-8</value>
</list>
</property>
</bean>
</list>
</property>
</bean>
</beans>
bean初始化+静态工具
线程安全的单例（懒汉模式）
基于jdk的spring的RestTemplate
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Lazy;
import org.springframework.http.client.SimpleClientHttpRequestFactory;
import org.springframework.http.converter.FormHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
import org.springframework.stereotype.Component;
import org.springframework.web.client.DefaultResponseErrorHandler;
import org.springframework.web.client.RestTemplate;
import javax.annotation.PostConstruct;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
/**
* @title：基于jdk的spring的RestTemplate
* @author：liuxing
* @date：2015-05-18 09:35
*/
@Component
@Lazy(false)
public class SimpleRestClient {
private static final Logger LOGGER = LoggerFactory.getLogger(SimpleRestClient.class);
private static RestTemplate restTemplate;
static {
SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
requestFactory.setReadTimeout(5000);
requestFactory.setConnectTimeout(5000);
// 添加转换器
List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
messageConverters.add(new StringHttpMessageConverter(Charset.forName("UTF-8")));
messageConverters.add(new FormHttpMessageConverter());
messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
messageConverters.add(new MappingJackson2HttpMessageConverter());
restTemplate = new RestTemplate(messageConverters);
restTemplate.setRequestFactory(requestFactory);
restTemplate.setErrorHandler(new DefaultResponseErrorHandler());
LOGGER.info("SimpleRestClient初始化完成");
}
private SimpleRestClient() {
}
@PostConstruct
public static RestTemplate getClient() {
return restTemplate;
}
}
使用Httpclient连接池的方式
import org.apache.http.Header;
import org.apache.http.client.HttpClient;
import org.apache.http.impl.client.DefaultConnectionKeepAliveStrategy;
import org.apache.http.impl.client.DefaultHttpRequestRetryHandler;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.message.BasicHeader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Lazy;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.http.converter.FormHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
import org.springframework.stereotype.Component;
import org.springframework.web.client.DefaultResponseErrorHandler;
import org.springframework.web.client.RestTemplate;
import javax.annotation.PostConstruct;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
/**
* @title：使用spring的restTemplate替代httpclient工具
* @author：liuxing
* @date：2015-05-18 08:48
*/
@Component
@Lazy(false)
public class RestClient {
private static final Logger LOGGER = LoggerFactory.getLogger(SimpleRestClient.class);
private static RestTemplate restTemplate;
static {
// 长连接保持30秒
PoolingHttpClientConnectionManager pollingConnectionManager = new PoolingHttpClientConnectionManager(30, TimeUnit.SECONDS);
// 总连接数
pollingConnectionManager.setMaxTotal(1000);
// 同路由的并发数
pollingConnectionManager.setDefaultMaxPerRoute(1000);
HttpClientBuilder httpClientBuilder = HttpClients.custom();
httpClientBuilder.setConnectionManager(pollingConnectionManager);
// 重试次数，默认是3次，没有开启
httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler(2, true));
// 保持长连接配置，需要在头添加Keep-Alive
httpClientBuilder.setKeepAliveStrategy(new DefaultConnectionKeepAliveStrategy());
// RequestConfig.Builder builder = RequestConfig.custom();
// builder.setConnectionRequestTimeout(200);
// builder.setConnectTimeout(5000);
// builder.setSocketTimeout(5000);
//
// RequestConfig requestConfig = builder.build();
// httpClientBuilder.setDefaultRequestConfig(requestConfig);
List<Header> headers = new ArrayList<>();
headers.add(new BasicHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.16 Safari/537.36"));
headers.add(new BasicHeader("Accept-Encoding", "gzip,deflate"));
headers.add(new BasicHeader("Accept-Language", "zh-CN"));
headers.add(new BasicHeader("Connection", "Keep-Alive"));
httpClientBuilder.setDefaultHeaders(headers);
HttpClient httpClient = httpClientBuilder.build();
// httpClient连接配置，底层是配置RequestConfig
HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);
// 连接超时
clientHttpRequestFactory.setConnectTimeout(5000);
// 数据读取超时时间，即SocketTimeout
clientHttpRequestFactory.setReadTimeout(5000);
// 连接不够用的等待时间，不宜过长，必须设置，比如连接不够用时，时间过长将是灾难性的
clientHttpRequestFactory.setConnectionRequestTimeout(200);
// 缓冲请求数据，默认值是true。通过POST或者PUT大量发送数据时，建议将此属性更改为false，以免耗尽内存。
// clientHttpRequestFactory.setBufferRequestBody(false);
// 添加内容转换器
List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
messageConverters.add(new StringHttpMessageConverter(Charset.forName("UTF-8")));
messageConverters.add(new FormHttpMessageConverter());
messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
messageConverters.add(new MappingJackson2HttpMessageConverter());
restTemplate = new RestTemplate(messageConverters);
restTemplate.setRequestFactory(clientHttpRequestFactory);
restTemplate.setErrorHandler(new DefaultResponseErrorHandler());
LOGGER.info("RestClient初始化完成");
}
private RestClient() {
}
@PostConstruct
public static RestTemplate getClient() {
return restTemplate;
}
}
HttpClientUtils
import com.dooioo.commons.Strings;
import com.dooioo.framework.SpringContextHolder;
import com.dooioo.ky.cache.HttpClientResultCache;
import org.apache.commons.collections.MapUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpEntity;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import java.util.Map;
/**
*
* 类功能说明：httpclient工具类,基于httpclient 4.x
* Title: HttpClientUtils.java
* @author 刘兴
* @date 2014-3-7 下午7:48:58
* @version V1.0
*/
public class HttpClientUtils {
private static final Logger LOGGER = LoggerFactory.getLogger(HttpClientUtils.class);
/**
* post请求
* @param url
* @param formParams
* @return
*/
public static String doPost(String url, Map<String, String> formParams) {
if (MapUtils.isEmpty(formParams)) {
return doPost(url);
}
try {
MultiValueMap<String, String> requestEntity = new LinkedMultiValueMap<>();
formParams.keySet().stream().forEach(key -> requestEntity.add(key, MapUtils.getString(formParams, key, "")));
return RestClient.getClient().postForObject(url, requestEntity, String.class);
} catch (Exception e) {
LOGGER.error("POST请求出错：{}", url, e);
}
return Strings.EMPTY;
}
/**
* post请求
* @param url
* @return
*/
public static String doPost(String url) {
try {
return RestClient.getClient().postForObject(url, HttpEntity.EMPTY, String.class);
} catch (Exception e) {
LOGGER.error("POST请求出错：{}", url, e);
}
return Strings.EMPTY;
}
/**
* get请求
* @param url
* @return
*/
public static String doGet(String url) {
try {
return RestClient.getClient().getForObject(url, String.class);
} catch (Exception e) {
LOGGER.error("GET请求出错：{}", url, e);
}
return Strings.EMPTY;
}
}
ErrorHolder
自定义的一个异常结果包装类
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.web.client.HttpClientErrorException;
import org.springframework.web.client.HttpServerErrorException;
/**
* @title：ErrorHolder
* @author：liuxing
* @date：2015-06-16 11:01
*/
public class ErrorHolder {
private HttpStatus statusCode;
private String statusText;
private String responseBody;
private HttpHeaders responseHeaders;
public ErrorHolder(HttpStatus statusCode, String statusText, String responseBody) {
this.statusCode = statusCode;
this.statusText = statusText;
this.responseBody = responseBody;
}
public ErrorHolder(String statusText) {
this.statusText = statusText;
}
public HttpStatus getStatusCode() {
return statusCode;
}
public void setStatusCode(HttpStatus statusCode) {
this.statusCode = statusCode;
}
public String getStatusText() {
return statusText;
}
public void setStatusText(String statusText) {
this.statusText = statusText;
}
public String getResponseBody() {
return responseBody;
}
public void setResponseBody(String responseBody) {
this.responseBody = responseBody;
}
public HttpHeaders getResponseHeaders() {
return responseHeaders;
}
public void setResponseHeaders(HttpHeaders responseHeaders) {
this.responseHeaders = responseHeaders;
}
public static ErrorHolder build(Exception exception) {
if (exception instanceof HttpServerErrorException) {
HttpServerErrorException e = (HttpServerErrorException) exception;
return new ErrorHolder(e.getStatusCode(), e.getStatusText(), e.getResponseBodyAsString());
}
if (exception instanceof HttpClientErrorException) {
HttpClientErrorException e = (HttpClientErrorException) exception;
return new ErrorHolder(e.getStatusCode(), e.getStatusText(), e.getResponseBodyAsString());
}
return new ErrorHolder(exception.getMessage());
}
}
使用样例
api里面可以做自动的参数匹配：
如：http://you domainn name/test?empNo={empNo}，则下面方法的最后一个参数为数据匹配参数，会自动根据key进行查找，然后替换
API没有声明异常，注意进行异常处理
更多使用语法请查看API文档
ResponseEntity<List<KyArea>> result = RestClient.getClient().exchange(DIVIDE_PLATE_API, HttpMethod.GET, HttpEntity.EMPTY, new ParameterizedTypeReference<List<KyArea>>() {}, map("empNo", empNo));
List<KyArea> list = result.getBody();
ResponseEntity<KyArea> result = RestClient.getClient().exchange(DIVIDE_PLATE_API, HttpMethod.GET, HttpEntity.EMPTY, KyArea.class, map("empNo", empNo));
KyArea kyArea = result.getBody();
更多
RestTemplate API说明和使用参考
http://docs.spring.io/spring/docs/4.1.x/javadoc-api/org/springframework/web/client/RestTemplate.html
HttpClient官方示例和参数配置说明
http://hc.apache.org/httpcomponents-client-4.4.x/examples.html
http://hc.apache.org/httpcomponents-client-4.4.x/tutorial/html/index.html
依赖
spring 3.x以上
<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-xml</artifactId>
<version>2.5.3</version>
</dependency>
<dependency>
<groupId>org.codehaus.jackson</groupId>
<artifactId>jackson-mapper-asl</artifactId>
<version>1.9.13</version>
</dependency>
注意点
1.关于httpclient配置的defaultMaxPerRoute和maxTotal
defaultMaxPerRoute：最大路由并发数，以主机为单位
maxTotal：整个连接池的并发数
例如：
defaultMaxPerRoute为10，maxTotal为100
假设只会访问http://www.baidu.com和http://www.google.com
那么能同时并发到客源的只能是10，房源也是10，整个连接永远不会到100
2.部分方法注意查看源码，默认构造里面会新增常用的数据转换器，spring对jackson比较情有独钟，在解析xml和json时，优先使用jackson
/**
* Create a new instance of the {@link RestTemplate} using default settings.
* Default {@link HttpMessageConverter}s are initialized.
*/
public RestTemplate() {
this.messageConverters.add(new ByteArrayHttpMessageConverter());
this.messageConverters.add(new StringHttpMessageConverter());
this.messageConverters.add(new ResourceHttpMessageConverter());
this.messageConverters.add(new SourceHttpMessageConverter<Source>());
this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
if (romePresent) {
this.messageConverters.add(new AtomFeedHttpMessageConverter());
this.messageConverters.add(new RssChannelHttpMessageConverter());
}
if (jackson2XmlPresent) {
messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
}
else if (jaxb2Present) {
this.messageConverters.add(new Jaxb2RootElementHttpMessageConverter());
}
if (jackson2Present) {
this.messageConverters.add(new MappingJackson2HttpMessageConverter());
}
else if (gsonPresent) {
this.messageConverters.add(new GsonHttpMessageConverter());
}
}
/**
* Create a new instance of the {@link RestTemplate} based on the given {@link ClientHttpRequestFactory}.
* @param requestFactory HTTP request factory to use
* @see org.springframework.http.client.SimpleClientHttpRequestFactory
* @see org.springframework.http.client.HttpComponentsClientHttpRequestFactory
*/
public RestTemplate(ClientHttpRequestFactory requestFactory) {
this();
setRequestFactory(requestFactory);
}
再看添加转换器的方法外部添加转换器时，this.messageConverters.clear();会先清除已有的，需要注意
/**
* Create a new instance of the {@link RestTemplate} using the given list of
* {@link HttpMessageConverter} to use
* @param messageConverters the list of {@link HttpMessageConverter} to use
* @since 3.2.7
*/
public RestTemplate(List<HttpMessageConverter<?>> messageConverters) {
Assert.notEmpty(messageConverters, "‘messageConverters‘ must not be empty");
this.messageConverters.addAll(messageConverters);
}
/**
* Set the message body converters to use.
* <p>These converters are used to convert from and to HTTP requests and responses.
*/
public void setMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
Assert.notEmpty(messageConverters, "‘messageConverters‘ must not be empty");
// Take getMessageConverters() List as-is when passed in here
if (this.messageConverters != messageConverters) {
this.messageConverters.clear();
this.messageConverters.addAll(messageConverters);
}
}
来自：http://liuxing.info/2015/05/21/RestTemplate%E5%AE%9E%E8%B7%B5/
http://www.open-open.com/lib/view/open1436018677419.html
以上是关于Spring提供的用于访问Rest服务的客户端：RestTemplate实践的主要内容，如果未能解决你的问题，请参考以下文章
用于内部 REST 通信的 OAuth + spring 安全性