提到Spring Cloud就不得不说起微服务
什么是微服务
Spring Cloud是一个微服务框架，相比Dubbo等RPC框架, Spring Cloud提供的全套的分布式系统解决方案。
Spring Cloud对微服务基础框架Netflix的多个开源组件进行了封装，同时又实现了和云端平台以及和Spring Boot开发框架的集成。
Spring Cloud为微服务架构开发涉及的配置管理，服务治理，熔断机制，智能路由，微代理，控
控制总线，一次性token，全局一致性锁，leader选举，分布式session，集群状态管理等操作提供了一种简单的开发方式。
Spring Cloud 为开发者提供了快速构建分布式系统的工具，开发者可以快速的启动服务或构建应用、同时能够快速和云平台资源进行对接。
简单说，微服务就是拒绝大型单体应用，基于业务边界进行服务微化拆分，各个服务独立部署运行
为什么使用Spring Cloud
SpringCloud是Spring旗下的项目之一，Spring最擅长继承，SpringCloud也是如此，它将目前非常流行的一些技术整合到一起，实现了诸如：配置管理，服务发现，智能路由，负载均衡，熔断器，控制总线，集群状态等功能，主要涉及以下组件：
集群、分布式、节点
集群是一个物理形态，分布式是一种工作方式，一堆机器可以叫做集群，是否协作不重要。《分布式系统原理与范型》定义：分布式系统是若干计算机的集合，这些计算机对于用户来说就像单个相关系统，分布式系统是建立在网络上的软件系统
分布式是指将几台服务器集中在一起，实现统一业务
分布式中的每一个节点都可以做集群，但集群并不一定是分布式的
节点：集群中的一个服务器
远程调用
分布式系统中，由于各个服务可能处于不同主机，但是服务之间不可避免的需要互相调用，我们称为远程调用
负载均衡
分布式系统中，A服务调用B服务，B服务在多台机器中都存在，A调用任意个服务器均可完成功能。提高网站健壮性
常用算法
轮询：为第一个请求选择第一个服务器，依次往后选择
最小连接：优先选择连接数最小，也就是压力最小的后端服务器
散列：根据请求源的IP的散列hash来选择要转发的服务器，可以在一定程度上保证特定的用户连接到相同的服务器
服务注册中心
A服务调用B服务，A服务并不知道B服务在哪几台服务器有，哪些正常的，哪些服务已经下线。解决这个问题，就引入了服务注册中心
如果某些服务下线，我们其他人可以实时感知到其他服务的状态，避免调用不可用的服务
配置中心
每个服务最终有大量的配置，并且每个服务都可能部署在多台机器上，我们经常需要变更配置，我们可以让每个服务去配置中心获取自己的配置
服务熔断&服务降级
在微服务架构中，微服务之间通过网络进行通信，存在相互依赖，当其中一个服务不可用，可能产生雪崩效应。
- 服务的熔断
a. 设置服务的超时，当被调用的服务经常失败到达某个阈值，我们可以开启断路保护机制，后来的请求不再去调用这个服务。本地直接返回默认的数据。 - 服务降级
a. 在运维期间，当系统处于高峰期，系统资源紧张，我们可以让非核心业务降级处理。降级：某些服务不处理，或者简单处理，返回null等
API网关
在微服务嫁狗证，网关作为整体架构的重要组件，他抽象了微服务中都需要的公共功能，同时提供了客户端负载均衡，服务自动熔断，灰度发布，统一认证，限流流控。
搭建服务提供方和调用方Demo
提供方
.pom.xml
<dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jdbc</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>2.1.1</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <scope>runtime</scope> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>tk.mybatis</groupId> <artifactId>mapper-spring-boot-starter</artifactId> <version>2.0.4</version> </dependency> </dependencies>
.UserMapper.java
public interface UserMapper extends Mapper<User> { }
.yml
server: port: 8081 spring.datasource: url: jdbc:mysql:///mysql?useUnicode=true&characterEncoding=utf8 username: root password: root mybatis: type-aliases-package: cn.jczb.service.pojo
User.java
@Table(name = "tb_user") public class User { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String userName; private String password; private String name; private Integer age; private Integer sex; private Date birthday; private Date created; private Date updated; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public Integer getSex() { return sex; } public void setSex(Integer sex) { this.sex = sex; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } public Date getCreated() { return created; } public void setCreated(Date created) { this.created = created; } public Date getUpdated() { return updated; } public void setUpdated(Date updated) { this.updated = updated; } @Override public String toString() { return "User{" + "id=" + id + ", userName='" + userName + '\'' + ", password='" + password + '\'' + ", name='" + name + '\'' + ", age=" + age + ", sex=" + sex + ", birthday=" + birthday + ", created=" + created + ", updated=" + updated + '}'; } }
UserService.java
@Service public class UserService { @Autowired private UserMapper userMapper; public User queryUserById(Long id){ return this.userMapper.selectByPrimaryKey(id); } }
UserController.java
@RestController @RequestMapping("user") public class UserController { @Autowired private UserService userService; @GetMapping("{id}") public User queryUserById(@PathVariable("id")Long id){ return this.userService.queryUserById(id); } }
调用方
.pom
<dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </dependency> </dependencies>
User实体同上
.UserController
@Controller @RequestMapping("consumer/user") public class UserController { @Autowired private RestTemplate restTemplate; @GetMapping @ResponseBody public User queryUserById(@RequestParam("id")Long id){ return this.restTemplate.getForObject("http://localhost:8081/user/" + id,User.class); } }
启动类
@SpringBootApplication public class JczbServiceConsumerApplication { @Bean public RestTemplate restTemplate(){ return new RestTemplate(); } public static void main(String[] args) { SpringApplication.run(JczbServiceConsumerApplication.class, args); } }
运行效果
错误
abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
at [Source: (PushbackInputStream); line: 1, column: 1]] with root cause
2020-02-06 09:54:09.179 ERROR 17544 --- [nio-8088-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.http.converter.HttpMessageConversionException: Type definition error: [simple type, class org.apache.catalina.User]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.apache.catalina.User` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information at [Source: (PushbackInputStream); line: 1, column: 1]] with root cause com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.apache.catalina.User` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information at [Source: (PushbackInputStream); line: 1, column: 1] at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67) ~[jackson-databind-2.9.7.jar:2.9.7] at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1452) ~[jackson-databind-2.9.7.jar:2.9.7] at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1028) ~[jackson-databind-2.9.7.jar:2.9.7] at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:265) ~[jackson-databind-2.9.7.jar:2.9.7] at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013) ~[jackson-databind-2.9.7.jar:2.9.7] at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3084) ~[jackson-databind-2.9.7.jar:2.9.7] at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:237) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:225) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:100) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:689) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:644) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:296) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at cn.jczb.service.controller.UserController.queryUserById(UserController.java:22) ~[classes/:na] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_162] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_162] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_162] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_162] at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:891) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:866) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) ~[spring-webmvc-5.0.10.RELEASE.jar:5.0.10.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.34.jar:8.5.34] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.10.RELEASE.jar:5.0.10.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498) [tomcat-embed-core-8.5.34.jar:8.5.34] at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.34.jar:8.5.34] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_162] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_162] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.34.jar:8.5.34] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_162]
原因
引用User类的jar包引入错误
应该引入了这个
This application has no explicit mapping for /error, so you are seeing this as a fallback.
This application has no explicit mapping for /error, so you are seeing this as a fallback. Thu Feb 06 19:21:47 CST 2020 There was an unexpected error (type=Internal Server Error, status=500). 500 : [{"timestamp":"2020-02-06T11:21:47.764+0000","status":500,"error":"Internal Server Error","message":"nested exception is org.apache.ibatis.exceptions.PersistenceException: \r\n### Error querying databa... (962 bytes)]
调用方Spring框架版本错误，改为和提供方一致的版本就可以了
<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.2.4.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent>
我的项目这样修改就可以了，目前没有问题
Demo 2
生产者
消费者
结果
但是我发现一个问题，生产者换成@Post之后就不可以直接在网址上访问了,报错如下
POST请求不可以用地址栏加参数访问吗？报错为参数不合法，还需要细细论证，有经验的欢迎交流哦！
