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="http://www.mamicode.com/10000"/>        <property name="connectTimeout" value="http://www.mamicode.com/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="http://www.mamicode.com/1000" />        <!--每个主机的并发-->        <property name="defaultMaxPerRoute" value="http://www.mamicode.com/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="http://www.mamicode.com/2"/>                <constructor-arg value="http://www.mamicode.com/true"/>            </bean>        </property>        <property name="defaultHeaders">            <list>                <bean class="org.apache.http.message.BasicHeader">                    <constructor-arg value="http://www.mamicode.com/User-Agent"/>                    <constructor-arg value="http://www.mamicode.com/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="http://www.mamicode.com/Accept-Encoding"/>                    <constructor-arg value="http://www.mamicode.com/gzip,deflate"/>                </bean>                <bean class="org.apache.http.message.BasicHeader">                    <constructor-arg value="http://www.mamicode.com/Accept-Language"/>                    <constructor-arg value="http://www.mamicode.com/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="http://www.mamicode.com/5000"/>        <!--读写超时时间，毫秒-->        <property name="readTimeout" value="http://www.mamicode.com/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

http://docs.spring.io/spring/docs/4.1.x/javadoc-api/org/springframework/http/client/SimpleClientHttpRequestFactory.html

http://docs.spring.io/spring/docs/4.1.x/javadoc-api/org/springframework/http/client/HttpComponentsClientHttpRequestFactory.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

Spring提供的用于访问Rest服务的客户端：RestTemplate实践