Spring Boot文档阅读笔记-EhCache的使用

﹏ヽ暗。殇╰゛Y 2023-01-13 05:40 212阅读 0赞

这里要先注意2个概念：

buffer和cache，很多人会讲这两个概念混用。但其实这是两个概念！

buffer：一般是指存储临时数据的实体。只能读写一次，对于程序员来说buffer是可见的，比如TCB中，接收tcp数据的buffer。

cache：对于程序员来说是不可见的。允许多次获取相同的数据。这也就是EhCache不叫EhBuffer的原因。

程序结构如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxNzg0NDI3NjE_size_16_color_FFFFFF_t_70][]

首先来看下pom.xml

<?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 https://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>2.1.10.RELEASE</version>
            <relativePath/> 
        </parent>
        <groupId>com.example</groupId>
        <artifactId>demo</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <name>demo</name>
        <description>Demo project for Spring Boot</description>
        <properties>
            <java.version>1.8</java.version>
        </properties>
        <dependencies>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <optional>true</optional>
            </dependency>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <scope>test</scope>
            </dependency>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-cache</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.ehcache</groupId>
                <artifactId>ehcache</artifactId>
            </dependency>
    
        </dependencies>
    
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                    <configuration>
                        <excludes>
                            <exclude>
                                <groupId>org.projectlombok</groupId>
                                <artifactId>lombok</artifactId>
                            </exclude>
                        </excludes>
                    </configuration>
                </plugin>
            </plugins>
        </build>
    
    </project>

下面是EhCache的配置

ehcache的配置文件需要放到资源文件下面，如上图的目录结构。

新建ehcache.xml内容如下：

<?xml version="1.0" encoding="UTF-8"?>
    <ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    	xsi:noNamespaceSchemaLocation="http://ehcache.org/ehcache.xsd">
    
    	
    	<defaultCache eternal="true" maxElementsInMemory="100"
    		overflowToDisk="false" memoryStoreEvictionPolicy="LFU" />
    
    	
    	<cache name="employee" maxElementsInMemory="10000"
    		eternal="false" overflowToDisk="false" memoryStoreEvictionPolicy="LFU" />
    </ehcache>

上面的xml配置了自定义的缓存配置，还指定了放入缓存的元素的最大个数。以及内存回收策略采用LFU（最不长使用）。并且还设置了如果内存满了要不要存到磁盘上。

下面是在application.properties中指定ehcache.xml文件路径：

spring.cache.ehcache.config=classpath:ehcache.xml

下面创建一个实体类，缓存中保存的就是这个实体类的数据（逻辑上是一个对象，物理上得看EhCache的存储规则）

Employee.java

@Data
    public class Employee {
    
        private int id;
        private String name;
        private String role;
    
        public Employee() {
        }
    
        public Employee(int id, String name, String role) {
            this.id = id;
            this.name = name;
            this.role = role;
        }
    }

下面是缓存服务层的代码：

@Service
    public class EmployeeService {
    
        @Cacheable(value = "employee")
        public List<Employee> getListOfEmployees(){
    
            System.out.println("getListOfEmployees is running...");
    
            List<Employee> employees = new ArrayList<Employee>(4);
    
            employees.add(new Employee(1000, "Sumit", "Manager"));
            employees.add(new Employee(1001, "Souvik", "Java Developer"));
            employees.add(new Employee(1002, "Liton", "SQl Developer"));
            employees.add(new Employee(1003, "Debina", "Leader"));
    
            return employees;
        }
    
        @Cacheable(value = "employee", key = "#name")
        public Employee findEmployeeByName(String name, List<Employee> employees) {
            System.out.println("findEmployeeByName is running...");
    
            for (Employee emp : employees) {
                if (emp.getName().equalsIgnoreCase(name)) {
                    return emp;
                }
            }
    
            return null;
        }
    }

@Cacheable：这个注解和ehcache.xml文件对应。如value为employee对应ehcache.xml中的

下面是启动类DemoApplication.java

@EnableCaching
    @SpringBootApplication
    public class DemoApplication implements CommandLineRunner {
    
        @Autowired
        private EmployeeService employeeService;
    
        public static void main(String[] args) {
    
            SpringApplication.run(DemoApplication.class, args);
        }
    
        @Override
        public void run(String... args) throws Exception {
    
            List<Employee> listOfEmployees = employeeService.getListOfEmployees();
            System.out.println(listOfEmployees);
            System.out.println("---------------------------------------------------");
    
            listOfEmployees = employeeService.getListOfEmployees();
            System.out.println(listOfEmployees);
            System.out.println("---------------------------------------------------");
    
            Employee employee = employeeService.findEmployeeByName("Sumit", listOfEmployees);
            System.out.println(employee);
            System.out.println("---------------------------------------------------");
    
            employee = employeeService.findEmployeeByName("Sumit", listOfEmployees);
            System.out.println(employee);
            System.out.println("---------------------------------------------------");
    
            employee = employeeService.findEmployeeByName("Liton", listOfEmployees);
            System.out.println(employee);
            System.out.println("---------------------------------------------------");
        }
    }

程序运行结果如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxNzg0NDI3NjE_size_16_color_FFFFFF_t_70 1][]

可见，前两次调用一样的数据，第二次是直接从缓存中拿的。

源码打包下载地址：

[https://github.com/fengfanchen/Java/tree/master/ehcacheDemo][https_github.com_fengfanchen_Java_tree_master_ehcacheDemo]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxNzg0NDI3NjE_size_16_color_FFFFFF_t_70 1]: /images/20221022/2145246193da49139205121b0afc0d96.png
[https_github.com_fengfanchen_Java_tree_master_ehcacheDemo]: https://github.com/fengfanchen/Java/tree/master/ehcacheDemo