一个连接池的例子（来自JIVE）（6）

答案：//文件：PropertyManager.java

//这个类其实没什么用了，可以去掉，但需要去掉前面几个类中对这个类的引用。
package com.qingtuo.db.pool;

import java.util.*;
import java.io.*;

/**
 * Manages properties for the entire Jive system. Properties are merely
 * pieces of information that need to be saved in between server restarts.
 * <p>
 * At the moment, properties are stored in a Java Properties file. In a version
 * of Jive coming soon, the properties file format will move to XML. XML
 * properties will allow hierarchical property structures which may mean the
 * API of this class will have to change.
 * <p>
 * Jive properties are only meant to be set and retrevied by core Jive classes.
 * Therefore, skin writers should probably ignore this class.
 * <p>
 * This class is implemented as a singleton since many classloaders seem to
 * take issue with doing classpath resource loading from a static context.
 */
public class PropertyManager {

    private static PropertyManager manager = null;
    private static Object managerLock = new Object();
    private static String propsName = "/pcc_2000.properties";

    /**
     * Returns a Jive property
     *
     * @param name the name of the property to return.
     * @returns the property value specified by name.
     */
    public static String getProperty(String name) {
        if (manager == null) {
            synchronized(managerLock) {
                if (manager == null) {
                    String sysname=System.getProperty("os.name").toUpperCase();
                    if(sysname.indexOf("WIN")!=-1){
                        propsName=propsName2000;
                    }
                    else{
                        propsName=propsNameLinux;
                    }
                    manager = new PropertyManager(propsName);
                }
            }
        }
        return manager.getProp(name);
    }

    /**
     * Sets a Jive property.
     *
     * @param name the name of the property being set.
     * @param value the value of the property being set.
     */
    public static void setProperty(String name, String value) {
        if (manager == null) {
            synchronized(managerLock) {
                if (manager == null) {
                    manager = new PropertyManager(propsName);
                }
            }
        }
        manager.setProp(name, value);
    }

    /**
     * Returns true if the properties are readable. This method is mainly
     * valuable at setup time to ensure that the properties file is setup
     * correctly.
     */
    public static boolean propertyFileIsReadable() {
        if (manager == null) {
            synchronized(managerLock) {
                if (manager == null) {
                    manager = new PropertyManager(propsName);
                }
            }
        }
        return manager.propFileIsReadable();
    }

    /**
     * Returns true if the properties are writable. This method is mainly
     * valuable at setup time to ensure that the properties file is setup
     * correctly.
     */
    public static boolean propertyFileIsWritable() {
        if (manager == null) {
            synchronized(managerLock) {
                if (manager == null) {
                    manager = new PropertyManager(propsName);
                }
            }
        }
        return manager.propFileIsWritable();
    }

    /**
     * Returns true if the jive.properties file exists where the path property
     * purports that it does.
     */
    public static boolean propertyFileExists() {
        if (manager == null) {
            synchronized(managerLock) {
                if (manager == null) {
                    manager = new PropertyManager(propsName);
  

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