Spring提供RestTemplate用于访问Rest服务的客户端实践

川长思鸟来 2022-06-14 01:06 240阅读 0赞

### 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 ###

### 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">
    
        
        <bean id="ky.pollingConnectionManager" class="org.apache.http.impl.conn.PoolingHttpClientConnectionManager">
            
            <property name="maxTotal" value="1000" />
            
            <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" />
            
            <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"/>
            
            <property name="connectTimeout" value="5000"/>
            
            <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][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_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_SimpleClientHttpRequestFactory.html]

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

[http://hc.apache.org/httpcomponents-client-4.4.x/tutorial/html/index.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][http_www.baidu.com_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);
        }
    }

[http_you]: http://you/
[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/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/SimpleClientHttpRequestFactory.html
[http_docs.spring.io_spring_docs_4.1.x_javadoc-api_org_springframework_http_client_HttpComponentsClientHttpRequestFactory.html]: http://docs.spring.io/spring/docs/4.1.x/javadoc-api/org/springframework/http/client/HttpComponentsClientHttpRequestFactory.html
[http_hc.apache.org_httpcomponents-client-4.4.x_examples.html]: http://hc.apache.org/httpcomponents-client-4.4.x/examples.html
[http_hc.apache.org_httpcomponents-client-4.4.x_tutorial_html_index.html]: http://hc.apache.org/httpcomponents-client-4.4.x/tutorial/html/index.html
[http_www.baidu.com_http_www.google.com]: http://www.baidu.com%e5%92%8chttp//www.google.com