configmanager.java

Java与模式 源代码

package com.javapatterns.singleton.demos;

import java.io.File;
import java.io.FileInputStream;
import java.util.Properties;

/**
 * Only once instance of the class may be created during the execution of any given program. Instances of this class should
 * be aquired through the getInstance() method. Notice that there are no public constructors for this class.
 */
public class ConfigManager
{
    /** The fully qualified name of the properties file */
    private static final String PFILE = System.getProperty("user.dir") + "/Singleton.properties";

    /** The File object corresponding to the file that contains the properties */
    private File mFile = null;

    /** The last modified time of the properties file */
    private long mLastModifiedTime = 0;

    /** The cached properties */
    private Properties mProps = null;

    /**
     * The only instance of this class
     * @label Creates
     */
    private static ConfigManager mInstance = new ConfigManager();

    /** The private constructor (enforces single instance) */
    private ConfigManager()
    {
        mFile = new File(PFILE);
        mLastModifiedTime = mFile.lastModified();

        if (mLastModifiedTime == 0)
        {
            System.err.println(PFILE + " file does not exist!");
        }

        mProps = new Properties();

        try
        {
            mProps.load(new FileInputStream(PFILE));
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    /**
     * Returns the singleton ConfigManager
     * @return The one and only instance of the ConfigManager
     */
    public static synchronized ConfigManager getInstance()
    {
        return mInstance;
    }

    /**
     * Gets a configuration item
     * @param name The name of the item
     * @param defaultVal The default value if name is not found
     * @return The value for the specified name
     */
    public final Object getConfigItem(String name, Object defaultVal)
    {
        long newTime = mFile.lastModified();

        // Check to see if configuration file has been modified
        // since the previous request. If so, then read in the new
        // contents
        if (newTime == 0)
        {
            // The props file was deleted or does not exist (!!)
            if (mLastModifiedTime == 0)
            {
                System.err.println(PFILE + " file does not exist!");
            }
            else
            {
                System.err.println(PFILE + " file was deleted!!");
            }
            return defaultVal;
        }
        else if (newTime > mLastModifiedTime)
        {
            mProps.clear(); // Get rid of the old properties
            try
            {
                mProps.load(new FileInputStream(PFILE));
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
        mLastModifiedTime = newTime;

        Object val = mProps.getProperty(name);
        if (val == null)
        {
            return defaultVal;
        }
        else
        {
            return val;
        }
    }
}