spring 配置統一管理，代碼可以直接運行。包含所有類和配置文件。

四個類

package com.wang;

/**
 * @ClassName: Config
 * @Description: TODO(這裏用一句話描述這個類的作用)
 * @author faicm
 * @date 2017年6月15日 下午8:56:17
 * 
 */
public class Config {
    private String user;
    private String pwd;
    private String name;
    public String getUser() {
        return user;
    }
    public void setUser(String user) {
        this.user = user;
    }
    public String getPwd() {
        return pwd;
    }
    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

package com.wang;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @ClassName: Main
 * @Description: TODO(這裏用一句話描述這個類的作用)
 * @author faicm
 * @date 2017年6月15日 下午8:58:27
 * 
 */
public class Main {
    public static void main(String[] args) {
        BeanFactory beanFactory = new ClassPathXmlApplicationContext("App.xml");
        Config config = beanFactory.getBean(Config.class);
        System.out.println(config.getUser());
        System.out.println(config.getPwd());
        System.out.println(config.getName());
    }
}

package com.wang;

import java.util.Properties;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;
import org.springframework.core.Constants;
import org.springframework.util.PropertyPlaceholderHelper.PlaceholderResolver;
import org.springframework.util.StringValueResolver;

public class MyPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer {

    // 下下下下下下這部分代碼只是爲了取出私有變量systemPropertiesMode爲了下面代碼使用，可以搜
    // systemPropertiesMode看到
    private int systemPropertiesMode = SYSTEM_PROPERTIES_MODE_FALLBACK;
    private static final Constants constants = new Constants(PropertyPlaceholderConfigurer.class);

    public void setSystemPropertiesModeName(String constantName) throws IllegalArgumentException {
        super.setSystemPropertiesModeName(constantName);
        this.systemPropertiesMode = constants.asNumber(constantName).intValue();
    }
    // 上上上上上上上上上上

    protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)
            throws BeansException {
        // 假設是從數據庫讀到的
        props.put("user", "來自數據庫user");
        props.put("name", "來自數據庫@注入");
        StringValueResolver valueResolver = new PlaceholderResolvingStringValueResolver(props);
        doProcessProperties(beanFactoryToProcess, valueResolver);
    }

    private class PlaceholderResolvingStringValueResolver implements StringValueResolver {

        private final MyPropertyPlaceholderHelper helper;

        private final PlaceholderResolver resolver;

        public PlaceholderResolvingStringValueResolver(Properties props) {
            this.helper = new MyPropertyPlaceholderHelper(placeholderPrefix, placeholderSuffix, valueSeparator,
                    ignoreUnresolvablePlaceholders);
            this.resolver = new PropertyPlaceholderConfigurerResolver(props);
        }

        public String resolveStringValue(String strVal) throws BeansException {
            String resolved = this.helper.replacePlaceholders(strVal, this.resolver);
            if (trimValues) {
                resolved = resolved.trim();
            }
            return (resolved.equals(nullValue) ? null : resolved);
        }
    }

    private class PropertyPlaceholderConfigurerResolver implements PlaceholderResolver {

        private final Properties props;

        private PropertyPlaceholderConfigurerResolver(Properties props) {
            this.props = props;
        }

        public String resolvePlaceholder(String placeholderName) {
            return MyPropertyPlaceholderConfigurer.this.resolvePlaceholder(placeholderName, props,
                    systemPropertiesMode);
        }
    }

}

package com.wang;

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

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.util.Assert;
import org.springframework.util.PropertyPlaceholderHelper.PlaceholderResolver;
import org.springframework.util.StringUtils;

/**
 * @ClassName: MyPropertyPlaceholderHelper
 * @Description: TODO(這裏用一句話描述這個類的作用)
 * @author faicm
 * @date 2017年6月15日 下午10:44:34
 * 
 */
public class MyPropertyPlaceholderHelper {

    private static final Log logger = LogFactory.getLog(MyPropertyPlaceholderHelper.class);

    private static final Map<String, String> wellKnownSimplePrefixes = new HashMap<String, String>(4);

    static {
        wellKnownSimplePrefixes.put("}", "{");
        wellKnownSimplePrefixes.put("]", "[");
        wellKnownSimplePrefixes.put(")", "(");
    }

    private final String placeholderPrefix;

    private final String placeholderSuffix;

    private final String simplePrefix;

    private final String valueSeparator;

    private final boolean ignoreUnresolvablePlaceholders;

    /**
     * Creates a new {@code PropertyPlaceholderHelper} that uses the supplied
     * prefix and suffix. Unresolvable placeholders are ignored.
     * 
     * @param placeholderPrefix
     *            the prefix that denotes the start of a placeholder
     * @param placeholderSuffix
     *            the suffix that denotes the end of a placeholder
     */
    public MyPropertyPlaceholderHelper(String placeholderPrefix, String placeholderSuffix) {
        this(placeholderPrefix, placeholderSuffix, null, true);
    }

    /**
     * Creates a new {@code PropertyPlaceholderHelper} that uses the supplied
     * prefix and suffix.
     * 
     * @param placeholderPrefix
     *            the prefix that denotes the start of a placeholder
     * @param placeholderSuffix
     *            the suffix that denotes the end of a placeholder
     * @param valueSeparator
     *            the separating character between the placeholder variable and
     *            the associated default value, if any
     * @param ignoreUnresolvablePlaceholders
     *            indicates whether unresolvable placeholders should be ignored
     *            ({@code true}) or cause an exception ({@code false})
     */
    public MyPropertyPlaceholderHelper(String placeholderPrefix, String placeholderSuffix, String valueSeparator,
            boolean ignoreUnresolvablePlaceholders) {

        Assert.notNull(placeholderPrefix, "'placeholderPrefix' must not be null");
        Assert.notNull(placeholderSuffix, "'placeholderSuffix' must not be null");
        this.placeholderPrefix = placeholderPrefix;
        this.placeholderSuffix = placeholderSuffix;
        String simplePrefixForSuffix = wellKnownSimplePrefixes.get(this.placeholderSuffix);
        if (simplePrefixForSuffix != null && this.placeholderPrefix.endsWith(simplePrefixForSuffix)) {
            this.simplePrefix = simplePrefixForSuffix;
        } else {
            this.simplePrefix = this.placeholderPrefix;
        }
        this.valueSeparator = valueSeparator;
        this.ignoreUnresolvablePlaceholders = ignoreUnresolvablePlaceholders;
    }

    /**
     * Replaces all placeholders of format {@code ${name}} with the
     * corresponding property from the supplied {@link Properties}.
     * 
     * @param value
     *            the value containing the placeholders to be replaced
     * @param properties
     *            the {@code Properties} to use for replacement
     * @return the supplied value with placeholders replaced inline
     */
    public String replacePlaceholders(String value, final Properties properties) {
        Assert.notNull(properties, "'properties' must not be null");
        return replacePlaceholders(value, new PlaceholderResolver() {
            public String resolvePlaceholder(String placeholderName) {
                return properties.getProperty(placeholderName);
            }
        });
    }

    public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
        Assert.notNull(value, "'value' must not be null");
        return parseStringValue(value, placeholderResolver, new HashSet<String>());
    }

    protected String parseStringValue(String strVal, PlaceholderResolver placeholderResolver,
            Set<String> visitedPlaceholders) {
        String str = this.parseStringValue1(strVal, placeholderResolver, visitedPlaceholders);
        if (str != null && str.startsWith("@{") && str.endsWith("}")) {
            return this.parseStringValue2(strVal, placeholderResolver, visitedPlaceholders);
        }
        return str;
    }

    protected String parseStringValue1(String strVal, PlaceholderResolver placeholderResolver,
            Set<String> visitedPlaceholders) {
        StringBuilder result = new StringBuilder(strVal);
        int startIndex = strVal.indexOf(this.placeholderPrefix);
        while (startIndex != -1) {
            int endIndex = findPlaceholderEndIndex(result, startIndex);
            if (endIndex != -1) {
                String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
                String originalPlaceholder = placeholder;
                if (!visitedPlaceholders.add(originalPlaceholder)) {
                    throw new IllegalArgumentException(
                            "Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
                }
                placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
                String propVal = placeholderResolver.resolvePlaceholder(placeholder);
                if (propVal == null && this.valueSeparator != null) {
                    int separatorIndex = placeholder.indexOf(this.valueSeparator);
                    if (separatorIndex != -1) {
                        String actualPlaceholder = placeholder.substring(0, separatorIndex);
                        String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
                        propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
                        if (propVal == null) {
                            propVal = defaultValue;
                        }
                    }
                }
                if (propVal != null) {
                    propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
                    result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
                    if (logger.isTraceEnabled()) {
                        logger.trace("Resolved placeholder '" + placeholder + "'");
                    }
                    startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length());
                } else if (this.ignoreUnresolvablePlaceholders) {
                    // Proceed with unprocessed value.
                    startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
                } else {
                    throw new IllegalArgumentException("Could not resolve placeholder '" + placeholder + "'"
                            + " in string value \"" + strVal + "\"");
                }
                visitedPlaceholders.remove(originalPlaceholder);
            } else {
                startIndex = -1;
            }
        }

        return result.toString();
    }

    protected String parseStringValue2(String strVal, PlaceholderResolver placeholderResolver,
            Set<String> visitedPlaceholders) {
        StringBuilder result = new StringBuilder(strVal);
        int startIndex = strVal.indexOf("@{");
        while (startIndex != -1) {
            int endIndex = findPlaceholderEndIndex(result, startIndex);
            if (endIndex != -1) {
                String placeholder = result.substring(startIndex + "@{".length(), endIndex);
                String originalPlaceholder = placeholder;
                if (!visitedPlaceholders.add(originalPlaceholder)) {
                    throw new IllegalArgumentException(
                            "Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
                }
                placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
                String propVal = placeholderResolver.resolvePlaceholder(placeholder);
                if (propVal == null && this.valueSeparator != null) {
                    int separatorIndex = placeholder.indexOf(this.valueSeparator);
                    if (separatorIndex != -1) {
                        String actualPlaceholder = placeholder.substring(0, separatorIndex);
                        String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
                        propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
                        if (propVal == null) {
                            propVal = defaultValue;
                        }
                    }
                }
                if (propVal != null) {
                    propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
                    result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
                    if (logger.isTraceEnabled()) {
                        logger.trace("Resolved placeholder '" + placeholder + "'");
                    }
                    startIndex = result.indexOf("@{", startIndex + propVal.length());
                } else if (this.ignoreUnresolvablePlaceholders) {
                    // Proceed with unprocessed value.
                    startIndex = result.indexOf("@{", endIndex + this.placeholderSuffix.length());
                } else {
                    throw new IllegalArgumentException("Could not resolve placeholder '" + placeholder + "'"
                            + " in string value \"" + strVal + "\"");
                }
                visitedPlaceholders.remove(originalPlaceholder);
            } else {
                startIndex = -1;
            }
        }

        return result.toString();
    }

    private int findPlaceholderEndIndex(CharSequence buf, int startIndex) {
        int index = startIndex + this.placeholderPrefix.length();
        int withinNestedPlaceholder = 0;
        while (index < buf.length()) {
            if (StringUtils.substringMatch(buf, index, this.placeholderSuffix)) {
                if (withinNestedPlaceholder > 0) {
                    withinNestedPlaceholder--;
                    index = index + this.placeholderSuffix.length();
                } else {
                    return index;
                }
            } else if (StringUtils.substringMatch(buf, index, this.simplePrefix)) {
                withinNestedPlaceholder++;
                index = index + this.simplePrefix.length();
            } else {
                index++;
            }
        }
        return -1;
    }
}

app.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
    http://www.springframework.org/schema/beans 
    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd  
                http://www.springframework.org/schema/context 
                http://www.springframework.org/schema/context/spring-context-4.3.xsd  
                ">
    <bean class="com.wang.MyPropertyPlaceholderConfigurer">
        <property name="locations">
            <value>classpath:jdbc.properties</value>
        </property>
        <property name="fileEncoding">
            <value>UTF-8</value>
        </property>
    </bean>

    <bean class="com.wang.Config">
        <property name="user" value="${user}" />
        <property name="pwd" value="${pwd}" />
        <property name="name" value="@{name}" />
    </bean>
</beans> 

user=來自配置文件user
pwd=來自配置文件pwd