PropertyPlaceholderConfigurer讀取配置文件

時間 2019-11-20

標籤 propertyplaceholderconfigurer 讀取配置文件简体版

原文原文鏈接

1. PropertyPlaceholderConfigurer是個bean工廠後置處理器的實現，也就是 BeanFactoryPostProcessor接口的一個實現。PropertyPlaceholderConfigurer能夠將上下文（配置文件）中的屬性值放在另外一個單獨的標準java Properties文件中去。在XML文件中用${key}替換指定的properties文件中的值。這樣的話，只須要對properties文件進行修改，而不用對xml配置文件進行修改。javascript

2.在Spring中，使用PropertyPlaceholderConfigurer能夠在XML配置文件中加入外部屬性文件，固然也能夠指定外部文件的編碼，如：html

 1 <bean id="propertyConfigurer"class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
 2    <property name="location">
 3      <value>conf/jdbc.properties</value>
 4    </property>
 5     <property name="fileEncoding">
 6       <value>UTF-8</value>
 7     </property>
 8 </bean>
 9 
10

3.PropertyPlaceholderConfigurer起的做用就是將佔位符指向的數據庫配置信息放在bean中定義的工具。java

4.查看源代碼，能夠發現，locations屬性定義在PropertyPlaceholderConfigurer的祖父類 PropertiesLoaderSupport中，而location只有 setter方法。相似於這樣的配置，在spring的源程序中很常見的。spring

PropertyPlaceholderConfigurer若是在指定的Properties文件中找不到你想使用的屬性，它還會在Java的System類屬性中查找。數據庫

咱們能夠經過System.setProperty(key, value)或者java中經過-Dnamevalue來給Spring配置文件傳遞參數。api

實例：oracle

<bean class="com.slp.util.SpringContextHolder"/>
        <bean id="propertyConfigurer"
        class="com.slp.util.CustomizedPropertyConfigurer">
        <property name="locations">
            <list>
                <value>classpath:conf/jdbc.properties</value>                <value>classpath:conf/config.properties</value>                <value>classpath:conf/server.properties</value>
            </list>
        </property>
        <property name="fileEncoding" value="UTF-8"/>
    </bean>

package com.slp.util;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;

import java.util.HashMap;
import java.util.Map;
import java.util.Properties;

public class CustomizedPropertyConfigurer extends PropertyPlaceholderConfigurer {

    private static Map<String,String> ctxPropMap;

    @Override
    protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props) throws BeansException {
        super.processProperties(beanFactoryToProcess, props);
        ctxPropMap = new HashMap<>();
        for (Object key : props.keySet()){
            String keyStr = key.toString();
            String value = String.valueOf(props.get(keyStr));
            ctxPropMap.put(keyStr,value);
        }
    }

    public static String getCtxProp(String name) {
        return ctxPropMap.get(name);
    }

    public static Map<String, String> getCtxPropMap() {
        return ctxPropMap;
    }
}

//使用的時候以下便可
CustomizedPropertyConfigurer.getCtxProp("xxx")

org.springframework.beans.factory.configapp

Class PropertyPlaceholderConfigurer

java.lang.Object-->ide

org.springframework.core.io.support.PropertiesLoaderSupport-->工具

org.springframework.beans.factory.config.PropertyResourceConfigurer-->

org.springframework.beans.factory.config.PlaceholderConfigurerSupport-->

org.springframework.beans.factory.config.PropertyPlaceholderConfigurer

以上即是PropertyPlaceholderConfigurer類的繼承關係，

All Implemented Interfaces:所實現的接口

Aware, BeanFactoryAware, BeanNameAware, BeanFactoryPostProcessor, Ordered, PriorityOrdered

Direct Known Subclasses:(直接的已知的子類)

PreferencesPlaceholderConfigurer

直接的子類：PreferencesPlaceholderConfigurer

public class PropertyPlaceholderConfigurer

extends PlaceholderConfigurerSupport

PlaceholderConfigurerSupport subclass that resolves ${...} placeholders against local properties and/or system properties and environment variables.

PlaceholderConfigurerSupport 的子類是用於解決${}的佔位符，好比本地變量或者系統變量或者環境變量等。

As of Spring 3.1, PropertySourcesPlaceholderConfigurer should be used preferentially over this implementation; it is more flexible through taking advantage of the Environment and PropertySource mechanisms also made available in Spring 3.1.

從spring3.1開始，propertysourcesplaceholderconfigurer應該在這些實現中優先使用，經過利用Environment 和PropertySource機制使得其更靈活。

PropertyPlaceholderConfigurer is still appropriate(合適的) for use when:

the spring-context module is not available (i.e., one is using Spring's BeanFactory API as opposed to ApplicationContext).
existing configuration makes use of the "systemPropertiesMode" and/or "systemPropertiesModeName" properties. Users are encouraged to move away from using these settings, and rather configure property source search order through the container's Environment; however, exact preservation of functionality may be maintained by continuing to use PropertyPlaceholderConfigurer.

Prior to Spring 3.1, the <context:property-placeholder/> namespace element registered an instance of PropertyPlaceholderConfigurer. It will still do so if using the spring-context-3.0.xsd definition of the namespace. That is, you can preserve registration of PropertyPlaceholderConfigurer through the namespace, even if using Spring 3.1; simply do not update your xsi:schemaLocation and continue using the 3.0 XSD.

在spring3.1以前<context:property-placeholder/> 命名空間註冊了一個PropertyPlaceholderConfigurer的實例，若是你使用spring-context-3.0.xsd 以前依然是能夠使用。

示例：例如一些配置文件中的常量爲了簡化不用頻繁的更改參數配置信息，spring3.0中提供了一種簡單的方式context:property-placeholder 元素。

只須要在spring的配置文件裏添加一句：<context:property-placeholder location=」」/>便可。這裏的location值爲參數配置文件的位置，參數配置文件與經常使用的參數配置文件相同，即鍵值對的形式。

PropertyPlaceholderConfiguration內置的功能很是豐富，若是未找到${xxx}中定義的xxx鍵，他還會去JVM系統屬性(System.getProperty())和環境變量(System.getenv())中尋找，經過啓用systemPropertiesMode和searchSystemEnviroment屬性，能夠控制這一行爲。

Since:

02.10.2003

Author:

Juergen Hoeller, Chris Beams

Field Summary

Fields
Modifier and Type	Field and Description
static int	SYSTEM_PROPERTIES_MODE_FALLBACK Check system properties if not resolvable in the specified properties.檢查系統配置文件若是給定的配置文件沒有該屬性。
static int	SYSTEM_PROPERTIES_MODE_NEVER Never check system properties.從不檢查系統屬性。
static int	SYSTEM_PROPERTIES_MODE_OVERRIDE Check system properties first, before trying the specified properties.在檢查特定的配置文件以前先檢查系統配置文件。

Fields inherited from class org.springframework.beans.factory.config.PlaceholderConfigurerSupport

Fields inherited from class org.springframework.core.io.support.PropertiesLoaderSupport

Fields inherited from interface org.springframework.core.Ordered

Constructor Summary

Constructors

Constructor and Description

PropertyPlaceholderConfigurer()

Method Summary

All MethodsInstance Methods Concrete Methods
Modifier and Type	Method and Description
protected void	processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props) Visit each bean definition in the given bean factory and attempt to replace ${...} property placeholders with values from the given properties. 訪問bean工廠裏面定義的全部bean並試圖去使用給定的配置文件中的值去替換${}佔位符。
protected String	resolvePlaceholder(String placeholder, Properties props) Resolve the given placeholder using the given properties.使用給定的配置文件替換佔位符。
protected String	resolvePlaceholder(String placeholder, Properties props, int systemPropertiesMode) Resolve the given placeholder using the given properties, performing a system properties check according to the given mode.
protected String	resolveSystemProperty(String key) Resolve the given key as JVM system property, and optionally also as system environment variable if no matching system property has been found.
void	setSearchSystemEnvironment(boolean searchSystemEnvironment) Set whether to search for a matching system environment variable if no matching system property has been found.
void	setSystemPropertiesMode(int systemPropertiesMode) Set how to check system properties: as fallback, as override, or never.
void	setSystemPropertiesModeName(String constantName) Set the system property mode by the name of the corresponding constant, e.g.

Methods inherited from class org.springframework.beans.factory.config.PlaceholderConfigurerSupport

Methods inherited from class org.springframework.beans.factory.config.PropertyResourceConfigurer

Methods inherited from class org.springframework.core.io.support.PropertiesLoaderSupport

Methods inherited from class java.lang.Object

Field Detail

SYSTEM_PROPERTIES_MODE_NEVER

public static final int SYSTEM_PROPERTIES_MODE_NEVER

Never check system properties.

See Also:

Constant Field Values

SYSTEM_PROPERTIES_MODE_FALLBACK

public static final int SYSTEM_PROPERTIES_MODE_FALLBACK

Check system properties if not resolvable in the specified properties. This is the default.

See Also:

Constant Field Values

SYSTEM_PROPERTIES_MODE_OVERRIDE

public static final int SYSTEM_PROPERTIES_MODE_OVERRIDE

Check system properties first, before trying the specified properties. This allows system properties to override any other property source.

See Also:

Constant Field Values

Constructor Detail

PropertyPlaceholderConfigurer

public PropertyPlaceholderConfigurer()

Method Detail

setSystemPropertiesModeName

public void setSystemPropertiesModeName(String constantName)

throws IllegalArgumentException

Set the system property mode by the name of the corresponding constant, e.g. "SYSTEM_PROPERTIES_MODE_OVERRIDE".

Parameters:

constantName - name of the constant

Throws:

IllegalArgumentException - if an invalid constant was specified

See Also:

setSystemPropertiesMode(int)

setSystemPropertiesMode

public void setSystemPropertiesMode(int systemPropertiesMode)

Set how to check system properties: as fallback, as override, or never. For example, will resolve ${user.dir} to the "user.dir" system property.

The default is "fallback": If not being able to resolve a placeholder with the specified properties, a system property will be tried. "override" will check for a system property first, before trying the specified properties. "never" will not check system properties at all.

setSearchSystemEnvironment

public void setSearchSystemEnvironment(boolean searchSystemEnvironment)

Set whether to search for a matching system environment variable if no matching system property has been found. Only applied when "systemPropertyMode" is active (i.e. "fallback" or "override"), right after checking JVM system properties.

Default is "true". Switch this setting off to never resolve placeholders against system environment variables. Note that it is generally recommended to pass external values in as JVM system properties: This can easily be achieved in a startup script, even for existing environment variables.

NOTE: Access to environment variables does not work on the Sun VM 1.4, where the corresponding System.getenv(java.lang.String) support was disabled - before it eventually got re-enabled for the Sun VM 1.5. Please upgrade to 1.5 (or higher) if you intend to rely on the environment variable support.

resolvePlaceholder

protected String resolvePlaceholder(String placeholder,Properties props,int systemPropertiesMode)

Resolve the given placeholder using the given properties, performing a system properties check according to the given mode.

The default implementation delegates to resolvePlaceholder (placeholder, props) before/after the system properties check.

Subclasses can override this for custom resolution strategies, including customized points for the system properties check.

Parameters:

placeholder - the placeholder to resolve

props - the merged properties of this configurer

systemPropertiesMode - the system properties mode, according to the constants in this class

Returns:

the resolved value, of null if none

resolvePlaceholder

protected String resolvePlaceholder(String placeholder, Properties props)

Resolve the given placeholder using the given properties. The default implementation simply checks for a corresponding property key.

Subclasses can override this for customized placeholder-to-key mappings or custom resolution strategies, possibly just using the given properties as fallback.

Note that system properties will still be checked before respectively after this method is invoked, according to the system properties mode.

Parameters:

placeholder - the placeholder to resolve

props - the merged properties of this configurer

Returns:

the resolved value, of null if none

See Also:

setSystemPropertiesMode(int)