浅析PropertySource 基本使用

目录
一、PropertySource 简介
二、@PropertySource与Environment读取配置文件
三、@PropertySource与@Value读取配置文件
四、@PropertySource 与 @Import
一、PropertySource 简介​ org.springframework.context.annotation.PropertySource 是一个注解,可以标记在类上、接口上、枚举上,在运行时起作用。而@Repeatable(value = PropertySources.class) 表示在PropertySources 中此注解时可以重复使用的。如下:
二、@PropertySource与Environment读取配置文件​
此注解@PropertySource 为Spring 中的 Environment提供方便和声明机制,通常与Configuration一起搭配使用。新建一个maven 项目,添加pom.xml 依赖:

<?xml version="1.0" encoding="UTF-8"?>


4.0.0

<groupId>com.spring.propertysource</groupId>
<artifactId>spring-propertysource</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>spring-propertysource</name>
<description>Demo project for Spring Boot</description>

<properties>
    <java.version>1.8</java.version>
    <spring.version>4.3.13.RELEASE</spring.version>
</properties>

<dependencies>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>${spring.version}</version>
    </dependency>

</dependencies>

<build>
    <pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.2</version>
                <configuration>
                    <source>1.6</source>
                    <target>1.6</target>
                </configuration>
            </plugin>
        </plugins>
    </pluginManagement>
</build>
一般把版本名称统一定义在 标签中,便于统一管理,如上可以通过${…} 来获取指定版本。定义一个application.properties 来写入如下配置com.spring.name=liuXuan com.spring.age=18新建一个TestBean,定义几个属性public class TestBean {
private String name;
private Integer age;

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;
}

@Override
public String toString() {
    return "TestBean{" +
            "name='" + name + '\'' +
            ", age=" + age +
            '}';
}

}新建一个main class ,用来演示@PropertySource 的使用 @Configuration
@PropertySource(value = “classpath:application.properties”,ignoreResourceNotFound = false)
public class SpringPropertysourceApplication {

@Resource
Environment environment;

@Bean
public TestBean testBean(){
  TestBean testBean = new TestBean();
  // 读取application.properties中的name
  testBean.setName(environment.getProperty("com.spring.name"));
  // 读取application.properties中的age
  testBean.setAge(Integer.valueOf(environment.getProperty("com.spring.age")));
  System.out.println("testBean = " + testBean);
  return testBean;
}

public static void main(String[] args) {
  ApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringPropertysourceApplication.class);
  TestBean testBean = (TestBean)applicationContext.getBean("testBean");

}

}输出:testBean = TestBean{name=‘liuXuan’, age=18}
Refreshing the spring context@Configuration : 相当于 标签,注意不是,一个配置类可以有多个bean,但是只能有一个@PropertySource: 用于引入外部属性配置,和Environment 配合一起使用。其中ignoreResourceNotFound 表示没有找到文件是否会报错,默认为false,就是会报错,一般开发情况应该使用默认值,设置为true相当于生吞异常,增加排查问题的复杂性.引入PropertySource,注入Environment,然后就能用environment 获取配置文件中的value值。
三、@PropertySource与@Value读取配置文件@Value 基本使用​
我们以DB的配置文件为例,来看一下如何使用@Value读取配置文件首先新建一个DBConnection,具体代码如下: // 组件bean
@Component
@PropertySource(“classpath:db.properties”)
public class DBConnection {

@Value("${DB_DRIVER_CLASS}")
private String driverClass;

@Value("${DB_URL}")
private String dbUrl;

@Value("${DB_USERNAME}")
private String userName;

@Value("${DB_PASSWORD}")
private String password;

public DBConnection(){}

public void printDBConfigs(){
  System.out.println("Db Driver Class = " + driverClass);
  System.out.println("Db url = " + dbUrl);
  System.out.println("Db username = " + userName);
  System.out.println("Db password = " + password);
}

}类上加入@Component 表示这是一个组件bean,需要被spring进行管理,@PropertySource 用于获取类路径下的db.properties 配置文件,@Value用于获取properties中的key 对应的value值,printDBConfigs方法打印出来对应的值。新建一个db.properties,具体文件如下#MYSQL Database Configurations
DB_DRIVER_CLASS=com.mysql.jdbc.Driver
DB_URL=jdbc:mysql://localhost:3306/test
DB_USERNAME=cxuan
DB_PASSWORD=111111
APP_NAME=PropertySourceExample这是一个MYSQL连接数据库驱动的配置文件。新建一个SpringMainClass,用于测试DBConection中是否能够获取到@Value的值 public class SpringMainClass {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
        // 注解扫描,和@ComponentScan 和 基于XML的配置<context:component-scan base-package>相同
        context.scan("com.spring.propertysource.app");

        // 刷新上下文环境
        context.refresh();
        System.out.println("Refreshing the spring context");

        // 获取DBConnection这个Bean,调用其中的方法
        DBConnection dbConnection = context.getBean(DBConnection.class);
        dbConnection.printDBConfigs();

        // 关闭容器(可以省略,容器可以自动关闭)
        context.close();
    }
}输出:Refreshing the spring context

Db Driver Class = com.mysql.jdbc.Driver
Db url = jdbc:mysql://localhost:3306/test
Db username = cxuan
Db password = 111111@Value 高级用法​ 在实现了上述的例子之后,我们再来看一下@Value 的高级用法:@Value 可以直接为字段赋值,例如:@Value(“cxuan”)
String name;

@Value(10)
Integer age;

@Value("APPNAMENOTFOUND:Default")privateStringdefaultAppName;@Value@Value("{APP_NAME_NOT_FOUND:Default}") private String defaultAppName;@Value 可以直接获取系统属性,例如:@Value("APPN​AMEN​OTF​OUND:Default")privateStringdefaultAppName;@Value可以直接获取系统属性,例如:@Value("{java.home}")
// @Value("#{systemProperties[‘java.home’]}") SPEL 表达式
String javaHome;

@Value("${HOME}")
String dir;@Value 可以注解在方法和参数上@Value(“Test”) // 可以直接使用Test 进行单元测试
public void printValues(String s, @Value(“another variable”) String v) {

}修改DBConnection后的代码如下:public class DBConnection {

@Value("${DB_DRIVER_CLASS}")
private String driverClass;

@Value("${DB_URL}")
private String dbUrl;

@Value("${DB_USERNAME}")
private String userName;

@Value("${DB_PASSWORD}")
private String password;

public DBConnection(){}

public void printDBConfigs(){
    System.out.println("Db Driver Class = " + driverClass);
    System.out.println("Db url = " + dbUrl);
    System.out.println("Db username = " + userName);
    System.out.println("Db password = " + password);
}

}在com.spring.propertysource.app 下 新增DBConfiguration,作用是配置管理类,管理DBConnection,并读取配置文件,代码如下:@Configuration
@PropertySources({
@PropertySource(“classpath:db.properties”),
@PropertySource(value = “classpath:root.properties”, ignoreResourceNotFound = true)
})
public class DBConfiguration {

@Value("Default DBConfiguration")
private String defaultName;

@Value("true")
private boolean defaultBoolean;

@Value("10")
private int defaultInt;

@Value("${APP_NAME_NOT_FOUND:Default}")
private String defaultAppName;

 @Value("#{systemProperties['java.home']}")

// @Value("${java.home}")
private String javaHome;

@Value("${HOME}")
private String homeDir;

@Bean
public DBConnection getDBConnection() {
    DBConnection dbConnection = new DBConnection();
    return dbConnection;
}

@Value("Test") // 开启测试
public void printValues(String s, @Value("another variable") String v) {
    System.out.println("Input Argument 1 = " + s);
    System.out.println("Input Argument 2 = " + v);

    System.out.println("Home Directory = " + homeDir);
    System.out.println("Default Configuration Name = " + defaultName);
    System.out.println("Default App Name = " + defaultAppName);
    System.out.println("Java Home = " + javaHome);
    System.out.println("Home dir = " + homeDir);
    System.out.println("Boolean = " + defaultBoolean);
    System.out.println("Int = " + defaultInt);

}

}使用SpringMainClass 进行测试,测试结果如下:Input Argument 1 = Test
Input Argument 2 = another variable
Home Directory = /Users/mr.l
Default Configuration Name = Default DBConfiguration
Default App Name = Default
Java Home = /Library/Java/JavaVirtualMachines/jdk1.8.0_191.jdk/Contents/Home/jre
Home dir = /Users/mr.l
Boolean = true
Int = 10
Refreshing the spring contextDb Driver Class = com.mysql.jdbc.Driver
Db url = jdbc:mysql://localhost:3306/test
Db username = cxuan
Db password = 111111可以看到上述代码并没有显示调用printValues 方法,默认是以单元测试的方式进行的。​
四、@PropertySource 与 @Import​
@Import 可以用来导入 @PropertySource 标注的类,具体代码如下:新建一个PropertySourceReadApplication 类,用于读取配置文件并测试,具体代码如下:// 导入BasicPropertyWithJavaConfig类
@Import(BasicPropertyWithJavaConfig.class)
public class PropertySourceReadApplication {

@Resource
private Environment env;

@Value("${com.spring.name}")
private String name;

@Bean("context")
public PropertySourceReadApplication contextLoadInitialized(){
    // 用environment 读取配置文件
    System.out.println(env.getProperty("com.spring.age"));
    // 用@Value 读取配置文件
    System.out.println("name = " + name);
    return null;
}

public static void main(String[] args) {
    // AnnotationConnfigApplicationContext 内部会注册Bean
    new AnnotationConfigApplicationContext(PropertySourceReadApplication.class);
}

}新建一个BasicPropertyWithJavaConfig 类,用于配置类并加载配置文件@Configuration
@PropertySource(value = “classpath:application.properties”)
public class BasicPropertyWithJavaConfig {

public BasicPropertyWithJavaConfig(){
    super();
}

}启动PropertySourceReadApplication ,console能够发现读取到配置文件中的value值18
name = cxuan

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