<!-- 加載spring boot redis包 -->
<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

② 在Spring Boot核心配置文件application.properties中配置redis連接信息

完整application.properties配置文件如下：



#配置內(nèi)嵌Tomcat端口號
server.port=9090

#配置項目上下文根
server.servlet.context-path=/016-springboot-redis

#配置連接MySQL數(shù)據(jù)庫信息
spring.datasource.url=jdbc:mysql://192.168.92.134:3306/springboot?useUnicode=true&characterEncoding=UTF-8&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.username=root
spring.datasource.password=123456


#配置視圖解析器
spring.mvc.view.prefix=/
spring.mvc.view.suffix=.jsp


#配置redis連接信息(單機模式)
spring.redis.host=192.168.92.134
spring.redis.port=6379
spring.redis.password=123456

③ 啟動redis服務

④ RedisController類

RestController
public class RedisController {

    @Autowired
    private StudentService studentService;


    /**
     * 請求地址：http://localhost:9090/016-springboot-redis//springboot/allStudentCount
     * @param request
     * @return
     */
    @GetMapping(value = "/springboot/allStudentCount")
    public Object allStudentCount(HttpServletRequest request) {

        Long allStudentCount = studentService.queryAllStudentCount();

        return "學生總?cè)藬?shù)：" + allStudentCount;
    }
}

⑤ StudentService接口

public interface StudentService {

    /**
     * 獲取學生總?cè)藬?shù)
     * @return
     */
    Long queryAllStudentCount();
}

⑥ 在StudentServiceImpl中注入RedisTemplate并修改根據(jù)id獲取學生的方法配置了上面的步驟，Spring Boot將自動配置RedisTemplate，在需要操作redis的類中注入redisTemplate即可。

注意：Spring Boot幫我們注入RedisTemplate類，泛型里面只能寫、或者什么都不寫。

@Service("studentServiceImpl")
public class StudentServiceImpl implements StudentService {

    @Autowired
    private StudentMapper studentMapper;

    @Autowired
    private RedisTemplate redisTemplate;

    @Override
    public Long queryAllStudentCount() {

        //設置redisTemplate對象key的序列化方式
        redisTemplate.setKeySerializer(new StringRedisSerializer());

        //從redis緩存中獲取總?cè)藬?shù)
        Long allStudentCount = (Long) redisTemplate.opsForValue().get("allStudentCount");

        //判斷是否為空
        if (null == allStudentCount) {

            //去數(shù)據(jù)庫查詢，并存放到redis緩存中
            allStudentCount = studentMapper.selectAllStudentCount();

            redisTemplate.opsForValue().set("allStudentCount",allStudentCount,15, TimeUnit.SECONDS);

        }


        return allStudentCount;
    }
}

⑦ 啟動類Application在SpringBoot啟動類上添加掃描數(shù)據(jù)持久層的注解并指定掃描包

@SpringBootApplication
@MapperScan(basePackages = "com.bjpowernode.springboot.mapper")//掃描數(shù)據(jù)持久層
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

⑧ 讓Student類實現(xiàn)序列化接口(可選)在類名上Alt + 回車，如果沒有提示生成序列化id，那么需要做如下的配置

⑨ 啟動SpringBoot應用，訪問測試

⑩ 打開Redis Desktop Mananger查看Redis中的情況

緩存穿透現(xiàn)象

項目名稱：017-springboot-redis-synchronized

首先通過MyBatis逆向工程生成實體bean和數(shù)據(jù)持久層。

1.pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.bjpowernode.springboot</groupId>
    <artifactId>017-springboot-redis-synchronized</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <name>017-springboot-redis-synchronized</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <!--SpringBoot web項目起步依賴-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <!--MyBatis集成SpringBoot框架的起步依賴-->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.0.0</version>
        </dependency>

        <!--連接MySQL的驅(qū)動-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>

        <!-- 加載spring boot redis包 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>

        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                </includes>
            </resource>
        </resources>

        <plugins>

            <!--mybatis代碼自動生成插件-->
            <plugin>
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.3.7</version>
                <configuration>
                    <!--配置文件的位置-->
                    <configurationFile>GeneratorMapper.xml</configurationFile>
                    <verbose>true</verbose>
                    <overwrite>true</overwrite>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

2.核心配置文件application.properties

#配置內(nèi)嵌Tomcat端口號
server.port=9090

#配置項目上下文根
server.servlet.context-path=/017-springboot-redis-synchronized

#配置MySQL數(shù)據(jù)庫連接
spring.datasource.url=jdbc:mysql://192.168.92.134:3306/springboot?useUnicode=true&characterEncoding=UTF-8&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.username=root
spring.datasource.password=123456

#配置redis緩存
spring.redis.host=192.168.92.134
spring.redis.port=6379
spring.redis.password=123456

#配置SpringMVC視圖解析器
spring.mvc.view.prefix=/
spring.mvc.view.suffix=.jsp

3.Dao數(shù)據(jù)持久層

4.Service業(yè)務層

@Service("studentServiceImpl")
public class StudentServiceImpl implements StudentService {

    @Autowired
    private StudentMapper studentMapper;

    @Autowired
    private RedisTemplate<Object,Object> redisTemplate;

    @Override
    public Long queryAllStudentCount() {

        //設置redis的key序列化方式
        redisTemplate.setKeySerializer(new StringRedisSerializer());

        //從redis中獲取學生總?cè)藬?shù)
        Long allStudentCount = (Long) redisTemplate.opsForValue().get("allStudentCount");

        //判斷是否為空
        if (null == allStudentCount) {

            System.out.println("查詢數(shù)據(jù)庫。。。。。");

            //從數(shù)據(jù)庫查詢
            allStudentCount = studentMapper.selectAllStudentCount();

            //將值再存放到redis緩存中
            redisTemplate.opsForValue().set("allStudentCount", allStudentCount, 15, TimeUnit.HOURS);
        } else {

            System.out.println("查找Redis。。。。。");
        }

        return allStudentCount;
    }
}

5.Controller層

@RestController
public class RedisController {

    @Autowired
    private StudentService studentService;

    @GetMapping(value = "/springBoot/student")
    public @ResponseBody Object student() {

        //線程池個數(shù)，一般建議是CPU內(nèi)核數(shù) 或者 CPU內(nèi)核數(shù)據(jù)*2
        ExecutorService executorService = Executors.newFixedThreadPool(8);

        for (int i = 0; i < 1000; i++) {
            executorService.submit(new Runnable() {
                @Override
                public void run() {
                  studentService.queryAllStudentCount();
                }
            });
        }


        return "學生總?cè)藬?shù)：" + studentService.queryAllStudentCount();
    }
}

6.啟動類

@SpringBootApplication
@MapperScan(basePackages = "com.bjpowernode.springboot.mapper")
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

7.啟動應用程序，瀏覽器訪問測試

8.造成的問題

Tip：多個線程都去查詢數(shù)據(jù)庫，這種現(xiàn)象就叫做緩存穿透，如果并發(fā)比較大，對數(shù)據(jù)庫的壓力過大，有可能造成數(shù)據(jù)庫宕機。

緩存穿透現(xiàn)象-解決方法

項目名稱：018-springboot-redis-synchronized

項目描述：018-springboot-redis-synchronized項目是在017-springboot-redis-synchronized項目基礎上進行解決緩存穿透現(xiàn)象

1. 修改StudentServiceImpl中的代碼


@Service("studentServiceImpl")
public class StudentServiceImpl implements StudentService {

    @Autowired
    private StudentMapper studentMapper;

    @Autowired
    private RedisTemplate<Object,Object> redisTemplate;

    @Override
    public Long queryAllStudentCount() {
        //設置redisTemplate對象的key的序列化方式
        redisTemplate.setKeySerializer(new StringRedisSerializer());

        //從redis緩存中獲取學生總?cè)藬?shù)
        Long allStudentCount = (Long) redisTemplate.opsForValue().get("allStudentCount");

        //判斷學生總?cè)藬?shù)是否為空
        if (null == allStudentCount) {

            //設置同步代碼塊
            synchronized (this) {

                //再次從redis緩存中獲取學生總?cè)藬?shù)
                allStudentCount = (Long) redisTemplate.opsForValue().get("allStudentCount");

                //雙重檢測判斷緩存中是否有數(shù)據(jù)
                if (null == allStudentCount) {

                    System.out.println("從數(shù)據(jù)庫獲取數(shù)據(jù)");

                    //從數(shù)據(jù)庫獲取學生總?cè)藬?shù)
                    allStudentCount = studentMapper.selectAllStudentCount();

                    //將此值存放到redis緩存中
                    redisTemplate.opsForValue().set("allStudentCount", allStudentCount, 15, TimeUnit.MINUTES);
                } else {

                    System.out.println("從Redis中獲取數(shù)據(jù)。。。。");

                }
            }

        } else {
            System.out.println("從Redis中獲取數(shù)據(jù)。。。。");
        }

        return allStudentCount;
    }
}

2. 啟動應用程序，瀏覽器訪問測試，查看控制臺輸出只有第一個線程查詢數(shù)據(jù)庫，其它線程查詢Redis緩存，這樣的解決的小問題就是第一批進來的用戶會有一個等待，但是這樣的影響可以忽略。

3. springboot集成Redis阻止緩存穿透，為什么要做雙層驗證

防止線程獲取到cpu執(zhí)行權(quán)限的時候，其他線程已經(jīng)將數(shù)據(jù)放到Redis中了，所以再次判斷；

不能將synchronized范圍擴大，因為如果Redis緩存中如果有數(shù)據(jù)，線程不應該同步，否則影響效率。

SpringBoot集成Redis哨兵模式

1. 在pom.xml中配置相關的jar依賴

這步我們前面已經(jīng)做過


<!-- 加載spring boot redis包 -->
<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

2. 在Springboot核心配置文件application.properties中配置redis連接信息

IP地址及master根據(jù)自己的情況進行修改


#哨兵模式redis集群配置（哨兵模式）
spring.redis.password=123456
spring.redis.sentinel.master=mymaster
spring.redis.sentinel.nodes=192.168.235.128:26380,192.168.235.128:26382,192.168.235.128:26384

3. 通過rz –y命令，用我提供的資源中的配置文件覆蓋Linux服務器上Redis的配置文件，注意根據(jù)自己機器的情況修改資源文件ip及引用的redis路徑

我們目前6384是主，6380和6382是從