rollerconfig.java

这个weblogging 设计得比较精巧

/*
 * RollerConfig.java
 *
 */

package org.roller.config;

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.StringWriter;
import java.util.Enumeration;
import java.util.Properties;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;


/**
 * This is the single entry point for accessing configuration properties
 * in Roller.
 *
 * @author Allen Gilliland
 */
public class RollerConfig {
    
    private static String default_config = "/roller.properties";
    private static String custom_config = "/roller-custom.properties";
    private static String custom_jvm_param = "roller.custom.config";
    private static File custom_config_file = null;
    
    private static Properties mConfig;
    
    private static Log mLogger =
            LogFactory.getFactory().getInstance(RollerConfig.class);
    
    
    /*
     * Static block run once at class loading
     *
     * We load the default properties and any custom properties we find
     */
    static {
        mConfig = new Properties();
        
        try {
            // we'll need this to get at our properties files in the classpath
            Class config_class = Class.forName("org.roller.config.RollerConfig");
            
            // first, lets load our default properties
            InputStream is = config_class.getResourceAsStream(default_config);
            mConfig.load(is);
            mLogger.info("successfully loaded default properties.");
            
            // now, see if we can find our custom config
            is = config_class.getResourceAsStream(custom_config);
            if(is != null) {
                mConfig.load(is);
                mLogger.info("successfully loaded custom properties file from classpath");
            } else {
                mLogger.info("no custom properties file found in classpath");
            }
            
            // finally, check for an external config file
            String env_file = System.getProperty(custom_jvm_param);
            if(env_file != null && env_file.length() > 0) {
                custom_config_file = new File(env_file);
                
                // make sure the file exists, then try and load it
                if(custom_config_file != null && custom_config_file.exists()) {
                    is = new FileInputStream(custom_config_file);
                    mConfig.load(is);
                    mLogger.info("successfully loaded custom properties from "+
                            custom_config_file.getAbsolutePath());
                } else {
                    mLogger.warn("failed to load custom properties from "+
                            custom_config_file.getAbsolutePath());
                }
                
            } else {
                mLogger.info("no custom properties file specified via jvm option");
            }
            
            // some debugging for those that want it
            if(mLogger.isDebugEnabled()) {
                mLogger.debug("RollerConfig looks like this ...");
                
                String key = null;
                Enumeration keys = mConfig.keys();
                while(keys.hasMoreElements()) {
                    key = (String) keys.nextElement();
                    mLogger.debug(key+"="+mConfig.getProperty(key));
                }
            }
            
        } catch (Exception e) {
            e.printStackTrace();
        }
        
    }
    
    
    // no, you may not instantiate this class :p
    private RollerConfig() {}
    
    
    /**
     * Retrieve a property value
     *
     * @param     key Name of the property
     * @return    String Value of property requested, null if not found
     **/
    public static String getProperty(String key) {
        mLogger.debug("Fetching property ["+key+"="+mConfig.getProperty(key)+"]");
        return mConfig.getProperty(key);
    }
    
    
    /**
     * Retrieve a property as a boolean ... defaults to false if there is an error
     **/
    public static boolean getBooleanProperty(String name) {
        
        // get the value first, then convert
        String value = RollerConfig.getProperty(name);
        
        if(value == null)
            return false;
        
        return (new Boolean(value)).booleanValue();
    }
    
    
    /**
     * Retrieve all property keys
     *
     * @return Enumeration A list of all keys
     **/
    public static Enumeration keys() {
        return mConfig.keys();
    }
    
    
    /**
     * Set the "uploads.dir" property at runtime.
     *
     * Properties are meant to be read-only, but we make this one exception
     * for now because we know that some people are still writing their
     * uploads to the webapp context and we can only get that path at runtime.
     */
    public static void setUploadsDir(String path) {
        
        // only do this if the user wants to use the webapp context
        if("${webapp.context}".equals(mConfig.getProperty("uploads.dir")))
            mConfig.setProperty("uploads.dir", path);
    }
    
}