线程按序交替 线程按序交替package com.yanxizhu; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /** * @description: 线程按序交替 * @date: 2022/3/19 14:47 * @version: 1.0 */ public class PrintInfo { public static void main(String[] args) { print print = new print(); new Thread(new Runnable() { @Override public void run() { for(int i=1;i<5;i++){ try { print.printA(i); } catch (InterruptedException e) { e.printStackTrace(); } } } },"A").start(); new Thread(new Runnable() { @Override public void run() { for(int i=1;i<5;i++){ try { print.printB(i); } catch (InterruptedException e) { e.printStackTrace(); } } } },"B").start(); new Thread(new Runnable() { @Override public void run() { for(int i=1;i<5;i++){ try { print.printC(i); } catch (InterruptedException e) { e.printStackTrace(); } } } },"C").start(); } } class print{ private int num =1; Lock lock = new ReentrantLock(); Condition condition1 = lock.newCondition(); Condition condition2 = lock.newCondition(); Condition condition3 = lock.newCondition(); public void printA(int i) throws InterruptedException { lock.lock(); try{ if(num != 1){ condition1.await(); } System.out.println("A=="+Thread.currentThread().getName()+"====i="+i); num=2; condition2.signal(); }finally { lock.unlock(); } } public void printB(int i) throws InterruptedException { lock.lock(); try{ if(num != 2){ condition2.await(); } System.out.println("B=="+Thread.currentThread().getName()+"====i="+i); num=3; condition3.signal(); }finally { lock.unlock(); } } public void printC(int i) throws InterruptedException { lock.lock(); try{ if(num != 3){ condition3.await(); } System.out.println("C=="+Thread.currentThread().getName()+"====i="+i); num=1; condition1.signal(); }finally { lock.unlock(); } } }打印结果：A==A====i=1 B==B====i=1 C==C====i=1 A==A====i=2 B==B====i=2 C==C====i=2 A==A====i=3 B==B====i=3 C==C====i=3 A==A====i=4 B==B====i=4 C==C====i=4

SpringBoot整合seata分布式事务(不适用高并发场景) Springboot整合seata分布式事务一、创建seata日志表-- 注意此处0.3.0+ 增加唯一索引 ux_undo_log CREATE TABLE `undo_log` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `branch_id` bigint(20) NOT NULL, `xid` varchar(100) NOT NULL, `context` varchar(128) NOT NULL, `rollback_info` longblob NOT NULL, `log_status` int(11) NOT NULL, `log_created` datetime NOT NULL, `log_modified` datetime NOT NULL, `ext` varchar(100) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `ux_undo_log` (`xid`,`branch_id`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;二、安装事务协调器（seata-server）1、下载地址 2、导入依赖<dependency> <groupId>com.alibaba.cloud</groupId> <artifactId>spring-cloud-starter-alibaba-seata</artifactId> </dependency>3、启动seata服务器4、seata文件说明registry.conf：注册中心配置。这里执行注册中西为nacos。type = "nacos"，config {执行seata配置数据放在那里，这里默认使用文件放配置数据。 type = "file"file.conf：seata默认配置信息存放这里。例如，事务日志存放地方配置## transaction log store, only used in server side store { ## store mode: file、db mode = "file" ## file store property file { ## store location dir dir = "sessionStore" # branch session size , if exceeded first try compress lockkey, still exceeded throws exceptions maxBranchSessionSize = 16384 # globe session size , if exceeded throws exceptions maxGlobalSessionSize = 512 # file buffer size , if exceeded allocate new buffer fileWriteBufferCacheSize = 16384 # when recover batch read size sessionReloadReadSize = 100 # async, sync flushDiskMode = async } ## database store property db { ## the implement of javax.sql.DataSource, such as DruidDataSource(druid)/BasicDataSource(dbcp) etc. datasource = "druid" ## mysql/oracle/postgresql/h2/oceanbase etc. dbType = "mysql" driverClassName = "com.mysql.jdbc.Driver" ## if using mysql to store the data, recommend add rewriteBatchedStatements=true in jdbc connection param url = "jdbc:mysql://127.0.0.1:3306/seata?rewriteBatchedStatements=true" user = "mysql" password = "mysql" minConn = 5 maxConn = 30 globalTable = "global_table" branchTable = "branch_table" lockTable = "lock_table" queryLimit = 100 } }三、自定义代理数据源注意：所有想要用到分布式事务的微服务使用seata DataSourceProxy代理自己的数据源。springboot默认使用的是Hikari数据源。DataSourceAutoConfiguration.java源代码：// // Source code recreated from a .class file by IntelliJ IDEA // (powered by FernFlower decompiler) // package org.springframework.boot.autoconfigure.jdbc; import javax.sql.DataSource; import javax.sql.XADataSource; import org.springframework.boot.autoconfigure.condition.AnyNestedCondition; import org.springframework.boot.autoconfigure.condition.ConditionMessage; import org.springframework.boot.autoconfigure.condition.ConditionOutcome; import org.springframework.boot.autoconfigure.condition.ConditionalOnClass; import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean; import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty; import org.springframework.boot.autoconfigure.condition.SpringBootCondition; import org.springframework.boot.autoconfigure.condition.ConditionMessage.Builder; import org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.Dbcp2; import org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.Generic; import org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.Hikari; import org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.OracleUcp; import org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.Tomcat; import org.springframework.boot.autoconfigure.jdbc.DataSourceInitializationConfiguration.InitializationSpecificCredentialsDataSourceInitializationConfiguration; import org.springframework.boot.autoconfigure.jdbc.DataSourceInitializationConfiguration.SharedCredentialsDataSourceInitializationConfiguration; import org.springframework.boot.autoconfigure.jdbc.metadata.DataSourcePoolMetadataProvidersConfiguration; import org.springframework.boot.context.properties.EnableConfigurationProperties; import org.springframework.boot.jdbc.DataSourceBuilder; import org.springframework.boot.jdbc.EmbeddedDatabaseConnection; import org.springframework.context.annotation.Condition; import org.springframework.context.annotation.ConditionContext; import org.springframework.context.annotation.Conditional; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; import org.springframework.context.annotation.ConfigurationCondition.ConfigurationPhase; import org.springframework.core.env.Environment; import org.springframework.core.type.AnnotatedTypeMetadata; import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType; import org.springframework.util.StringUtils; @Configuration( proxyBeanMethods = false ) @ConditionalOnClass({DataSource.class, EmbeddedDatabaseType.class}) @ConditionalOnMissingBean( type = {"io.r2dbc.spi.ConnectionFactory"} ) @EnableConfigurationProperties({DataSourceProperties.class}) @Import({DataSourcePoolMetadataProvidersConfiguration.class, InitializationSpecificCredentialsDataSourceInitializationConfiguration.class, SharedCredentialsDataSourceInitializationConfiguration.class}) public class DataSourceAutoConfiguration { public DataSourceAutoConfiguration() { } static class EmbeddedDatabaseCondition extends SpringBootCondition { private static final String DATASOURCE_URL_PROPERTY = "spring.datasource.url"; private final SpringBootCondition pooledCondition = new DataSourceAutoConfiguration.PooledDataSourceCondition(); EmbeddedDatabaseCondition() { } public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) { Builder message = ConditionMessage.forCondition("EmbeddedDataSource", new Object[0]); if (this.hasDataSourceUrlProperty(context)) { return ConditionOutcome.noMatch(message.because("spring.datasource.url is set")); } else if (this.anyMatches(context, metadata, new Condition[]{this.pooledCondition})) { return ConditionOutcome.noMatch(message.foundExactly("supported pooled data source")); } else { EmbeddedDatabaseType type = EmbeddedDatabaseConnection.get(context.getClassLoader()).getType(); return type == null ? ConditionOutcome.noMatch(message.didNotFind("embedded database").atAll()) : ConditionOutcome.match(message.found("embedded database").items(new Object[]{type})); } } private boolean hasDataSourceUrlProperty(ConditionContext context) { Environment environment = context.getEnvironment(); if (environment.containsProperty("spring.datasource.url")) { try { return StringUtils.hasText(environment.getProperty("spring.datasource.url")); } catch (IllegalArgumentException var4) { } } return false; } } static class PooledDataSourceAvailableCondition extends SpringBootCondition { PooledDataSourceAvailableCondition() { } public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) { Builder message = ConditionMessage.forCondition("PooledDataSource", new Object[0]); return DataSourceBuilder.findType(context.getClassLoader()) != null ? ConditionOutcome.match(message.foundExactly("supported DataSource")) : ConditionOutcome.noMatch(message.didNotFind("supported DataSource").atAll()); } } static class PooledDataSourceCondition extends AnyNestedCondition { PooledDataSourceCondition() { super(ConfigurationPhase.PARSE_CONFIGURATION); } @Conditional({DataSourceAutoConfiguration.PooledDataSourceAvailableCondition.class}) static class PooledDataSourceAvailable { PooledDataSourceAvailable() { } } @ConditionalOnProperty( prefix = "spring.datasource", name = {"type"} ) static class ExplicitType { ExplicitType() { } } } @Configuration( proxyBeanMethods = false ) @Conditional({DataSourceAutoConfiguration.PooledDataSourceCondition.class}) @ConditionalOnMissingBean({DataSource.class, XADataSource.class}) @Import({Hikari.class, Tomcat.class, Dbcp2.class, OracleUcp.class, Generic.class, DataSourceJmxConfiguration.class}) protected static class PooledDataSourceConfiguration { protected PooledDataSourceConfiguration() { } } @Configuration( proxyBeanMethods = false ) @Conditional({DataSourceAutoConfiguration.EmbeddedDatabaseCondition.class}) @ConditionalOnMissingBean({DataSource.class, XADataSource.class}) @Import({EmbeddedDataSourceConfiguration.class}) protected static class EmbeddedDatabaseConfiguration { protected EmbeddedDatabaseConfiguration() { } } } 导入很多数据源 @Import({Hikari.class, Tomcat.class, Dbcp2.class, OracleUcp.class, Generic.class, DataSourceJmxConfiguration.class})DataSourceConfiguration.java源代码@Configuration( proxyBeanMethods = false ) @ConditionalOnClass({HikariDataSource.class}) @ConditionalOnMissingBean({DataSource.class}) @ConditionalOnProperty( name = {"spring.datasource.type"}, havingValue = "com.zaxxer.hikari.HikariDataSource", matchIfMissing = true ) static class Hikari { Hikari() { } @Bean @ConfigurationProperties( prefix = "spring.datasource.hikari" ) HikariDataSource dataSource(DataSourceProperties properties) { HikariDataSource dataSource = (HikariDataSource)DataSourceConfiguration.createDataSource(properties, HikariDataSource.class); if (StringUtils.hasText(properties.getName())) { dataSource.setPoolName(properties.getName()); } return dataSource; } }自定义代理数据源配置：import com.zaxxer.hikari.HikariDataSource; import io.seata.rm.datasource.DataSourceProxy; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.util.StringUtils; import javax.sql.DataSource; /** * @description: Seata自定义代理数据源 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/3/12 14:41 * @version: 1.0 */ @Configuration public class MySeataConfig { @Autowired DataSourceProperties dataSourceProperties; @Bean public DataSource dataSource(DataSourceProperties dataSourceProperties){ HikariDataSource dataSource = dataSourceProperties.initializeDataSourceBuilder().type(HikariDataSource.class).build(); if (StringUtils.hasText(dataSourceProperties.getName())) { dataSource.setPoolName(dataSourceProperties.getName()); } return new DataSourceProxy(dataSource); } }四、复制seata配置文件到项目resources下主要复制seata里面的模板文件file.conf、registry.conf注意：file.conf 的 service.vgroup_mapping 配置必须和spring.application.name一致。vgroup_mapping.{应用名称}-fescar-service-group = "default"service{ vgroup_mapping.family-booking-fescar-service-group = "default" }family-booking:微服务名字也可以通过配置 spring.cloud.alibaba.seata.tx-service-group修改后缀，但是必须和file.conf中的配置保持一致五、使用在分布式事务入口方法加上全局事务注解@GlobalTransactional，远程调用方法上加本地事务注解@Transactional即可。@GlobalTransactional @Transactional public PageUtils queryPage(Map<String, Object> params) { //调用远程方法，另一个微服务的方法加上小事务@Transactional }六、使用场景不适用高并发的场景，适用普通的业务远程调用。seata默认是使用的AT模式。针对高并发场景还是的用柔性事务，消息队列、延迟队列，MQ中间件完成。

CompletableFuture异步编排 通过线程池性能稳定，也可以获取执行结果，并捕获异常。但是，在业务复杂情况下，一个异步调用可能会依赖于另一个异步调用的执行结果。因此我们可以使用completableFuture 异步编排方案。比如：一个业务场景，需要同时获取多个数据，如果同步线程挨个执行，则需要时间为所有线程执行时间的总和。如果我们使用异步线程执行，所需时间则为耗时最长那个异步线程的执行时间。如果多个异常线程之间还存在依赖关系，比如线程3需要线程1的执行结果，线程6依赖线程3、线程2，那这个问题怎么解决呢。那就可以使用completableFuture 异步编排方案实现。注意：completableFuture 是jdk1.8之后添加的一个功能。CompletableFuture接口:public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {public interface Future<V> {以前用到的FutureTask就是用到的Future可以得到返回结果public class FutureTask<V> implements RunnableFuture<V> {public interface RunnableFuture<V> extends Runnable, Future<V> { /** * Sets this Future to the result of its computation * unless it has been cancelled. */ void run(); }Future可以得到返回结果CompletableFuture随便一个方法，都接受一个Function public <U> CompletableFuture<U> applyToEither( CompletionStage<? extends T> other, Function<? super T, U> fn) { return orApplyStage(null, other, fn); }@FunctionalInterface public interface Function<T, R> {Function是一个@FunctionalInterface，所以对Lambda使用要熟悉。CompletableFuture异步编排问题多个异步线程远程调用会导致丢失请求头，原因是多个线程，通过拦截器不能获取其它线程的请求的heard信息。解决方案：每个线程共享自己的requestAttributes。自定义feign拦截器：import feign.RequestInterceptor; import feign.RequestTemplate; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.web.context.request.RequestContextHolder; import org.springframework.web.context.request.ServletRequestAttributes; import javax.servlet.http.HttpServletRequest; /** * @description: TODO * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/3/10 23:03 * @version: 1.0 */ @Configuration public class FamilyFegin { @Bean(name ="requestInterceptor") public RequestInterceptor requestInterceptor(){ return new RequestInterceptor() { @Override public void apply(RequestTemplate requestTemplate) { //RequestContextHolder拿到刚请求来的数据 ServletRequestAttributes requestAttributes = (ServletRequestAttributes)RequestContextHolder.getRequestAttributes(); System.out.println("requestAttributes线程"+Thread.currentThread().getId()); HttpServletRequest request = requestAttributes.getRequest(); System.out.println("调用feign之前"); if(request != null){ //同步请求头数据 String cookie = request.getHeader("Cookie");//老数据 //给新请求同步老请求的cookie requestTemplate.header("Cookie", cookie); } } }; } }web配置：因为需要拦截器生效import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.servlet.config.annotation.InterceptorRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurer; /** * @description: WEB配置 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/3/10 22:40 * @version: 1.0 */ public class FamilyWebConfig implements WebMvcConfigurer { @Autowired LoginUserInterceptor loginUserInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(loginUserInterceptor).addPathPatterns("/**"); } }CompletableFuture异步编排import org.springframework.web.context.request.RequestContextHolder; import org.springframework.web.context.request.ServletRequestAttributes; import java.util.concurrent.CompletableFuture; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; /** * @description: CompletableFuture异步编排 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/3/10 23:32 * @version: 1.0 */ public class MyCompletableFuture { public static ExecutorService executorService = Executors.newFixedThreadPool(10); public void myOpenFeign() throws ExecutionException, InterruptedException { System.out.println("主线程0"); //远程调用存在丢失请求头的问题，因为不在同一线程，导致自定义拦截器不能获取head信息。 //解决丢失请求头方案： ServletRequestAttributes requestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes(); //第一个异步任务 CompletableFuture<Void> oneFuture = CompletableFuture.runAsync(() -> { System.out.println("辅线程1"); //每个线程都共享一下自己的requestAttributes RequestContextHolder.setRequestAttributes(requestAttributes); //异步线程远程调用，业务1 //异步线程调用业务代码 }, executorService); //第二个异步任务 CompletableFuture<Void> twoFuture = CompletableFuture.runAsync(() -> { System.out.println("辅线程2"); //每个线程都共享一下自己的requestAttributes RequestContextHolder.setRequestAttributes(requestAttributes); //异步线程远程调用，业务2 //异步线程调用业务代码 }, executorService); CompletableFuture.allOf(oneFuture, twoFuture).get(); } }以上就是解决CompletableFuture异步编排，异步多线程引起的远程调用请求丢失解决方案。代码中共享requestAttributes原因ThreadLocal数据：ServletRequestAttributes requestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();RequestContextHolder主线程不一样获取的数据不一样，如下：import javax.faces.context.FacesContext; import org.springframework.core.NamedInheritableThreadLocal; import org.springframework.core.NamedThreadLocal; import org.springframework.lang.Nullable; import org.springframework.util.ClassUtils; public abstract class RequestContextHolder { private static final boolean jsfPresent = ClassUtils.isPresent("javax.faces.context.FacesContext", RequestContextHolder.class.getClassLoader()); private static final ThreadLocal<RequestAttributes> requestAttributesHolder = new NamedThreadLocal("Request attributes"); private static final ThreadLocal<RequestAttributes> inheritableRequestAttributesHolder = new NamedInheritableThreadLocal("Request context"); public RequestContextHolder() { }

Springboot拦截器配置 Springboot拦截器配置1、拦截器配置，主要实现HandlerInterceptor接口import org.springframework.stereotype.Component; import org.springframework.web.servlet.HandlerInterceptor; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * @description: 拦截器，配合FamilyWebConfig 配置使用 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/3/10 22:36 * @version: 1.0 */ @Component public class LoginUserInterceptor implements HandlerInterceptor { public static ThreadLocal<Object> objUser = new ThreadLocal<>(); @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { Object loginusr = request.getSession().getAttribute("LOGIN_USR"); if(loginusr != null){ objUser.set(loginusr); //登录了才能访问 return true; }else{ //没登录，跳转去登录 return false; } } } 由于拦截器需要配合web配置使用，因此创建web配置。2、web配置主要实现WebMvcConfigurer接口import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.servlet.config.annotation.InterceptorRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurer; /** * @description: WEB配置 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/3/10 22:40 * @version: 1.0 */ public class FamilyWebConfig implements WebMvcConfigurer { @Autowired LoginUserInterceptor loginUserInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(loginUserInterceptor).addPathPatterns("/**"); } }

JAVA面向对象有那些特征 JAVA面向对象有那些特征？面向对象编程是利用类和对象编程的一种思想。万物可归类，类是对于世界事物的高度抽象，不同的事物之间有不同的关系，一个类自身与外界的封装关系，一个父类和子类的继承关系，一个类和多个类的多态关系。万物皆对象，对象是具体的世界事物，面向对象的三大特征封装，继承，多态。封装，封装说明一个类行为和属性与其他类的关系，低耦合，高内聚；继承是父类和子类的关系，多态说的是类与类的关系。封装隐藏了类的内部实现机制，可以在不影响使用的情况下改变类的内部结构，同时也保护了数据。对外界而已它的内部细节是隐藏的，暴露给外界的只是它的访问方法。属性的封装：使用者只能通过事先定制好的方法来访问数据，可以方便地加入逻辑控制，限制对属性的不合理操作；方法的封装：使用者按照既定的方式调用方法，不必关心方法的内部实现，便于使用；便于修改，增强代码的可维护性；继承是从已有的类中派生出新的类，新的类能吸收已有类的数据属性和行为，并能扩展新的能力。在本质上是特殊~一般的关系，即常说的is-a关系。子类继承父类，表明子类是一种特殊的父类，并且具有父类所不具有的一些属性或方法。从多种实现类中抽象出一个基类，使其具备多种实现类的共同特性，当实现类用extends关键字继承了基类（父类）后，实现类就具备了这些相同的属性。继承的类叫做子类（派生类或者超类），被继承的类叫做父类（或者基类）。比如从猫类、狗类、虎类中可以抽象出一个动物类，具有和猫、狗、虎类的共同特性（吃、跑、叫等）。Java通过extends关键字来实现继承，父类中通过private定义的变量和方法不会被继承，不能在子类中直接操作父类通过private定义的变量以及方法。继承避免了对一般类和特殊类之间共同特征进行的重复描述，通过继承可以清晰地表达每一项共同特征所适应的概念范围，在一般类中定义的属性和操作适应于这个类本身以及它以下的每一层特殊类的全部对象。运用继承原则使得系统模型比较简练也比较清晰。相比于封装和继承，Java多态是三大特性中比较难的一个，封装和继承最后归结于多态，多态指的是类和类的关系，两个类由继承关系，存在有方法的重写，故而可以在调用时有父类引用指向子类对象。多态必备三个要素：继承，重写，父类引用指向子类对象。继承、封装：增强了代码的可复用性，多态：增加了可移植性、健壮性、灵活性。