spring自3.1版本后,增加了新的注解@PropertySource,用于注解注入配置文件的属性
以前,我们配置读取配置文件,一般都是在XML文件里面配置,其实,这不是很利于维护,毕竟要去XML里面找配置,还需要把对象注册为bean,让xml显得过于臃肿,如下就是以前读取xml读取properties文件的配置,相信不少同学都知道.
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<list>
<value>classpath:properties/config_userbean.properties</value>
<value>classpath:properties/config_mysql.properties</value>
</list>
</property>
</bean>
但是现在我们有注解的形式来配置了,让我们先来看一段源码,是关于注解@PropertySource注解的
image
从上面的注释,可以发现,@propertySource注解是自spring 3.1版本开始有的,是一个配置注解,用于注入properties文件的属性的.下面,开始上测试代码吧.
--------------------------------我是分割线--------------------------------------
先看配置文件里面的内容:
userBean.name=hexiaowu
userBean.sex=男
userBean.isflag=true</pre>
然后看测试注解注入的类:
@Component
@PropertySource(value = "classpath:properties/config_userbean.properties",ignoreResourceNotFound = true)
public class DemoAnnotation {
//注入peoperties文件里面的属性
@Value("${userBean.name}")
private String propertie_name;
/**
* 使用@value注解注入properties中的属性
* 1.在类名上面使用 @PropertySource("classpath:*") 注解,*代表属性文件路径,可以指向多个配置文件路径
* 如果是多个配置文件,则是 @PropertySource({"classpath:*","classpath:*"....})
* 2.ignoreResourceNotFound=true 表示如果配置文件不存在,则忽略报错
* 3.在字段上直接使用@value注解
* 4.注解内使用${userBean.name} userBean.name 代表属性文件里面的key
* 5.需要新增 PropertySourcesPlaceholderConfigurer 的bean
* 6.在 PropertySourcesPlaceholderConfigurer 增加@bean注解,申明返回的是一个bean,否则会注入不成功
*
*/
@Bean
public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer(){
return new PropertySourcesPlaceholderConfigurer();
}
public String getPropertie_name() {
return propertie_name;
}
public void setPropertie_name(String propertie_name) {
this.propertie_name = propertie_name;
}
@Override
public String toString() {
return "DemoAnnotation{" +
", propertie_name='" + propertie_name + '\'' +
'}';
有同学会很纳闷了,为什么要返回一个 PropertySourcesPlaceholderConfigurer 的bean呢?让我们来看看源码吧.
PS:因为前面本人对 PropertySourcesPlaceholderConfigurer 理解有误,导致下面解释的模棱两可,因为spring是通过PropertySourcesPlaceholderConfigurer 内locations来查找属性文件,然后在根据注解将匹配的属性set进去,而下面的注释解释,是表示用注解可以做一些什么操作..
public class PropertySourcesPlaceholderConfigurer extends PlaceholderConfigurerSupport
implements EnvironmentAware {
/**
* {@value} is the name given to the {@link PropertySource} for the set of
* {@linkplain #mergeProperties() merged properties} supplied to this configurer.
*/
public static final String LOCAL_PROPERTIES_PROPERTY_SOURCE_NAME = "localProperties";
/**
* {@value} is the name given to the {@link PropertySource} that wraps the
* {@linkplain #setEnvironment environment} supplied to this configurer.
*/
public static final String ENVIRONMENT_PROPERTIES_PROPERTY_SOURCE_NAME = "environmentProperties";
private MutablePropertySources propertySources;
private PropertySources appliedPropertySources;
private Environment environment;
下面代码省略.....</pre>
上面源码,并没能看出为什么一定要返回这个bean,那么我看就看看他的父类 PlaceholderConfigurerSupport 吧.以下是父类的源码
/**
* Abstract base class for property resource configurers that resolve placeholders
* in bean definition property values. Implementations <em>pull</em> values from a
* properties file or other {@linkplain org.springframework.core.env.PropertySource
* property source} into bean definitions.
*
* <p>The default placeholder syntax follows the Ant / Log4J / JSP EL style:
*
*<pre class="code">${...}</pre>
*
* Example XML bean definition:
*
*<pre class="code">{@code
*<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"/>
* <property name="driverClassName" value="}${driver}{@code "/>
* <property name="url" value="jdbc:}${dbname}{@code "/>
*</bean>
*}</pre>
*
* Example properties file:
*
* <pre class="code"> driver=com.mysql.jdbc.Driver
* dbname=mysql:mydb</pre>
*
* Annotated bean definitions may take advantage of property replacement using
* the {@link org.springframework.beans.factory.annotation.Value @Value} annotation:
*
*<pre class="code">@Value("${person.age}")</pre>
*
* Implementations check simple property values, lists, maps, props, and bean names
* in bean references. Furthermore, placeholder values can also cross-reference
* other placeholders, like:
*
*<pre class="code">rootPath=myrootdir
*subPath=${rootPath}/subdir</pre>
*
* In contrast to {@link PropertyOverrideConfigurer}, subclasses of this type allow
* filling in of explicit placeholders in bean definitions.
*
* <p>If a configurer cannot resolve a placeholder, a {@link BeanDefinitionStoreException}
* will be thrown. If you want to check against multiple properties files, specify multiple
* resources via the {@link #setLocations locations} property. You can also define multiple
* configurers, each with its <em>own</em> placeholder syntax. Use {@link
* #ignoreUnresolvablePlaceholders} to intentionally suppress throwing an exception if a
* placeholder cannot be resolved.
*
* <p>Default property values can be defined globally for each configurer instance
* via the {@link #setProperties properties} property, or on a property-by-property basis
* using the default value separator which is {@code ":"} by default and
* customizable via {@link #setValueSeparator(String)}.
*
* <p>Example XML property with default value:
*
*<pre class="code">{@code
* <property name="url" value="jdbc:}${dbname:defaultdb}{@code "/>
*}</pre>
*
* @author Chris Beams
* @author Juergen Hoeller
* @since 3.1
* @see PropertyPlaceholderConfigurer
* @see org.springframework.context.support.PropertySourcesPlaceholderConfigurer
*/
public abstract class PlaceholderConfigurerSupport extends PropertyResourceConfigurer
implements BeanNameAware, BeanFactoryAware {
/** Default placeholder prefix: {@value} */
public static final String DEFAULT_PLACEHOLDER_PREFIX = "${";
/** Default placeholder suffix: {@value} */
public static final String DEFAULT_PLACEHOLDER_SUFFIX = "}";
/** Default value separator: {@value} */
public static final String DEFAULT_VALUE_SEPARATOR = ":";
/** Defaults to {@value #DEFAULT_PLACEHOLDER_PREFIX} */
protected String placeholderPrefix = DEFAULT_PLACEHOLDER_PREFIX;
/** Defaults to {@value #DEFAULT_PLACEHOLDER_SUFFIX} */
protected String placeholderSuffix = DEFAULT_PLACEHOLDER_SUFFIX;
/** Defaults to {@value #DEFAULT_VALUE_SEPARATOR} */
protected String valueSeparator = DEFAULT_VALUE_SEPARATOR;
protected boolean ignoreUnresolvablePlaceholders = false;
protected String nullValue;
private BeanFactory beanFactory;
private String beanName;
类注释表示的是,该类所起的作用,替代了xml文件的哪些操作,我们只需要看下面定义的一个常量注解就能大概知道,为什么需要返回这么一个bean了.
类注释上有这么一句话:表示可以用带注释的bean,可以利用属性符号进行替换
* Annotated bean definitions may take advantage of property replacement using
* the {@link org.springframework.beans.factory.annotation.Value @Value} annotation:
*
*<pre class="code">@Value("${person.age}")
属性注释:
/** Default placeholder prefix: {@value} */
public static final String DEFAULT_PLACEHOLDER_PREFIX = "${";
/** Default placeholder suffix: {@value} */
public static final String DEFAULT_PLACEHOLDER_SUFFIX = "}";
/** Default value separator: {@value} */
public static final String DEFAULT_VALUE_SEPARATOR = ":";
/** Defaults to {@value #DEFAULT_PLACEHOLDER_PREFIX} */
protected String placeholderPrefix = DEFAULT_PLACEHOLDER_PREFIX;
/** Defaults to {@value #DEFAULT_PLACEHOLDER_SUFFIX} */
protected String placeholderSuffix = DEFAULT_PLACEHOLDER_SUFFIX;
/** Defaults to {@value #DEFAULT_VALUE_SEPARATOR} */
protected String valueSeparator = DEFAULT_VALUE_SEPARATOR;
protected boolean ignoreUnresolvablePlaceholders = false;
从上面注解可以发现,使用的 默认前缀是: '${', 而后缀是: '}' ,默认的分隔符是 ':', 但是set方法可以替换掉默认的分隔符,而 ignoreUnresolvablePlaceholders 默认为 false,表示会开启配置文件不存在,抛出异常的错误.
从上面就能看出这个bean所起的作用,就是将@propertySource注解的bean注入属性的作用,如果没有该bean,则不能解析${}符号.
下面是测试执行方法:
@Configuration
//扫描带有 @controller @service @Component 等spring注解的类注册为bean
@ComponentScan({"com.spring.annotation.annotationsAttribute"})
public class AnnotationsConfig {
public static void main(String[] args){
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AnnotationsConfig.class);
DemoAnnotation demoAnnotation = context.getBean(DemoAnnotation.class);
System.out.println(demoAnnotation.toString());
context.close();
}
}
打印结果为:
image
这就表示,我们的注入成功了
使用 @PropertySource注解需要注意以下几个地方
使用注解需要将类申明被扫描为一个bean,可以使用@Component 注解
@PropertySource(value = "classpath:properties/config_userbean.properties",ignoreResourceNotFound = true) 表示注入配置文件,并且忽略配置文件不存在的异常
必须返回一个 PropertySourcesPlaceholderConfigurer 的bean,否则,会不能识别@Value("{userBean.name}") 注解中的{userBean.name}指向的value,而会注入${userBean.name}的字符串,返回 PropertySourcesPlaceholderConfigurer 的方法,使用@Bean注解,表示返回的是个bean
在spring 4.0以后,spring增加了@PropertySources 注解,下面是源码
/**
* Container annotation that aggregates several {@link PropertySource} annotations.
*
* <p>Can be used natively, declaring several nested {@link PropertySource} annotations.
* Can also be used in conjunction with Java 8's support for <em>repeatable annotations</em>,
* where {@link PropertySource} can simply be declared several times on the same
* {@linkplain ElementType#TYPE type}, implicitly generating this container annotation.
*
* @author Phillip Webb
* @since 4.0
* @see PropertySource
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface PropertySources {
PropertySource[] value();
}
从源码的注释,可以看到自4.0以后,@PropertySources注解,可以使用多个@PropertySource注解,代码如下:
@PropertySources(
{
@PropertySource("classpath:properties/config_userbean.properties"),
@PropertySource("classpath:properties/config_mysql.properties")
}
)
有时候使用@PropertySource 注解会报 找不到这个注解的错误,但是spring确实是3.1以上版本,而且并不影响项目的使用,这样的话,可以使用@propertySources 注解嵌套@propertySource注解,这样就不会报错了
