env.java

传感器网络中的嵌入式操作系统源代码

// $Id: Env.java,v 1.3.4.1 2003/08/18 22:09:45 cssharp Exp $

package net.tinyos.util;

/**
 * The <code>Env</code> class provides an implementation of
 * <code>getenv</code> that actually works, unlike the one in
 * <code>java.lang.System</code>.  The class cannot be instantiated.
 *
 * V1.1: provide wrapper so that getenv doesn't fail horribly when the
 * native code is not found.
 *
 * @author   R M Yorston, David Gay
 * @version  1.1
 */
public class Env {
    static private boolean loaded;
    static {
	try {
	    java.lang.System.loadLibrary("getenv");
	    loaded = true;
	}
	catch (Throwable t) {
	    System.err.println("getenv JNI library not found. Env.getenv will not work");
	    System.err.println("(please consult installation directions in");
	    System.err.println("tinyos-1.x/tools/java/net/tinyos/util/Env.INSTALL)");
	}
    }

    private Env() {
    }

    /**
     * Gets an environment variable. An environment variable is a
     * system-dependent external variable that has a string value.
     *
     * @param	name	name of the environment variable
     * @return	the value of the variable, or <code>null</code> if the
     * variable is not defined.
     */
    public static String getenv(String name) {
	if (loaded) {
	    return igetenv(name);
	}
	else {
	    return null;
	}
    }

    private static native String igetenv(String name);
}