Spring —— web.xml 中用 PropertyPlaceholderConfigurer 类读取properties 文件或属性

傷城~ 2022-06-12 07:59 184阅读 0赞

**一、使用示例**

org.springframework.beans.factory.config.PropertyPlaceholderConfigurer 类用于读取某个位置的.properties 文件 或 properties 属性。

**1、spring-context.xml 中配置该类并加载文件**

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> 
 	<property name="locations"> 
 	<list> 
 	<value>classpath:META-INF/someProp.properties</value>
 	</list> 
 </property> 
 </bean>

注意属性名为locations，传入为list元素。之后会加载类路径下的META-INF目录下的someProp.propertes文件。

该文件中定义键值对，如：

name = 张无忌
    kongfu = 九阳神功

使用方式：

**2、加载pro 属性**  
加载pros 标签定义的键值对，不过多研究，对应该类属性值为：localProperties

**二、查看源码**

public abstract class PropertyResourceConfigurer extends PropertiesLoaderSupport
    		implements BeanFactoryPostProcessor, PriorityOrdered{}

PropertiesLoaderSupport 类代码如下：

package org.springframework.core.io.support;
 
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.util.Properties;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.core.io.Resource;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.DefaultPropertiesPersister;
 import org.springframework.util.PropertiesPersister;
 
 /**
 * Base class for JavaBean-style components that need to load properties
 * from one or more resources. Supports local properties as well, with
 * configurable overriding.
 *
 * @author Juergen Hoeller
 * @since 1.2.2
 */
 public abstract class PropertiesLoaderSupport {
 
 	public static final String XML_FILE_EXTENSION = ".xml";
 
 
 	/** Logger available to subclasses */
 	protected final Log logger = LogFactory.getLog(getClass());
 
 	private Properties[] localProperties;
 
 	private Resource[] locations;
 
 	private boolean localOverride = false;
 
 	private boolean ignoreResourceNotFound = false;
 
 	private String fileEncoding;
 
 	private PropertiesPersister propertiesPersister = new DefaultPropertiesPersister();
 
 
 	/**
 	 * Set local properties, e.g. via the "props" tag in XML bean definitions.
 	 * These can be considered defaults, to be overridden by properties
 	 * loaded from files.
 	 */
 	public void setProperties(Properties properties) {
 		this.localProperties = new Properties[] {properties};
 	}
 
 	/**
 	 * Set local properties, e.g. via the "props" tag in XML bean definitions,
 	 * allowing for merging multiple properties sets into one.
 	 */
 	public void setPropertiesArray(Properties[] propertiesArray) {
 		this.localProperties = propertiesArray;
 	}
 
 	/**
 	 * Set a location of a properties file to be loaded.
 	 * Can point to a classic properties file or to an XML file
 	 * that follows JDK 1.5's properties XML format.
 	 */
 	public void setLocation(Resource location) {
 		this.locations = new Resource[] {location};
 	}
 
 	/**
 	 * Set locations of properties files to be loaded.
 	 * Can point to classic properties files or to XML files
 	 * that follow JDK 1.5's properties XML format.
 	 * Note: Properties defined in later files will override
 	 * properties defined earlier files, in case of overlapping keys.
 	 * Hence, make sure that the most specific files are the last
 	 * ones in the given list of locations.
 	 */
 	public void setLocations(Resource[] locations) {
 		this.locations = locations;
 	}
 
 	/**
 	 * Set whether local properties override properties from files.
 	 * Default is "false": Properties from files override local defaults.
 	 * Can be switched to "true" to let local properties override defaults
 	 * from files.
 	 */
 	public void setLocalOverride(boolean localOverride) {
 		this.localOverride = localOverride;
 	}
 
 	/**
 	 * Set if failure to find the property resource should be ignored.
 	 * "true" is appropriate if the properties file is completely optional.
 	 * Default is "false".
 	 */
 	public void setIgnoreResourceNotFound(boolean ignoreResourceNotFound) {
 		this.ignoreResourceNotFound = ignoreResourceNotFound;
 	}
 
 	/**
 	 * Set the encoding to use for parsing properties files.
 	 * Default is none, using the <code>java.util.Properties</code>
 	 * default encoding.
 	 * Only applies to classic properties files, not to XML files.
 	 * @see org.springframework.util.PropertiesPersister#load
 	 */
 	public void setFileEncoding(String encoding) {
 		this.fileEncoding = encoding;
 	}
 
 	/**
 	 * Set the PropertiesPersister to use for parsing properties files.
 	 * The default is DefaultPropertiesPersister.
 	 * @see org.springframework.util.DefaultPropertiesPersister
 	 */
 	public void setPropertiesPersister(PropertiesPersister propertiesPersister) {
 		this.propertiesPersister =
 				(propertiesPersister != null ? propertiesPersister : new DefaultPropertiesPersister());
 	}
 
 
 	/**
 	 * Return a merged Properties instance containing both the
 	 * loaded properties and properties set on this FactoryBean.
 	 */
 	protected Properties mergeProperties() throws IOException {
 		Properties result = new Properties();
 
 		if (this.localOverride) {
 			// Load properties from file upfront, to let local properties override.
 			loadProperties(result);
 		}
 
 		if (this.localProperties != null) {
 			for (Properties localProp : this.localProperties) {
 				CollectionUtils.mergePropertiesIntoMap(localProp, result);
 			}
 		}
 
 		if (!this.localOverride) {
 			// Load properties from file afterwards, to let those properties override.
 			loadProperties(result);
 		}
 
 		return result;
 	}
 
 	/**
 	 * Load properties into the given instance.
 	 * @param props the Properties instance to load into
 	 * @throws java.io.IOException in case of I/O errors
 	 * @see #setLocations
 	 */
 	protected void loadProperties(Properties props) throws IOException {
 		if (this.locations != null) {
 			for (Resource location : this.locations) {
 				if (logger.isInfoEnabled()) {
 					logger.info("Loading properties file from " + location);
 				}
 				InputStream is = null;
 				try {
 					is = location.getInputStream();
 
 					String filename = null;
 					try {
 						filename = location.getFilename();
 					} catch (IllegalStateException ex) {
 						// resource is not file-based. See SPR-7552.
 					}
 
 					if (filename != null && filename.endsWith(XML_FILE_EXTENSION)) {
 						this.propertiesPersister.loadFromXml(props, is);
 					}
 					else {
 						if (this.fileEncoding != null) {
 							this.propertiesPersister.load(props, new InputStreamReader(is, this.fileEncoding));
 						}
 						else {
 							this.propertiesPersister.load(props, is);
 						}
 					}
 				}
 				catch (IOException ex) {
 					if (this.ignoreResourceNotFound) {
 						if (logger.isWarnEnabled()) {
 							logger.warn("Could not load properties from " + location + ": " + ex.getMessage());
 						}
 					}
 					else {
 						throw ex;
 					}
 				}
 				finally {
 					if (is != null) {
 						is.close();
 					}
 				}
 			}
 		}
 	}
 
 }