属性文件告诫尾随空格

仔细看看这两个看似完全相同的属性文件：

除非它们真的不相同：

（截图来自 Notepad ++）

由于保留尾随空格，lastName 的值在第一种情况下为 Smith，在第二种情况下为 Smith 。

很少这是用户期望的，而且只能推测为什么这是 Properties 类的默认行为。然而，创建 Properties 的增强版本可以很容易地解决这个问题。以下类 TrimmedProperties 就是这样做的。它是标准 Properties 类的直接替代品。

import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Map.Entry;
import java.util.Properties;

/**
 * Properties class where values are trimmed for trailing whitespace if the
 * properties are loaded from a file.
 *
 * <p>
 * In the standard {@link java.util.Properties Properties} class trailing
 * whitespace is always preserved. When loading properties from a file such
 * trailing whitespace is almost always <i>unintentional</i>. This class fixes
 * this problem. The trimming of trailing whitespace only takes place if the
 * source of input is a file and only where the input is line oriented (meaning
 * that for example loading from XML file is <i>not</i> changed by this class).
 * For this reason this class is almost in all cases a safe drop-in replacement
 * for the standard <tt>Properties</tt>
 * class.
 *
 * <p>
 * Whitespace is defined here as any of space (U+0020) or tab (U+0009).
 * * 
 */
public class TrimmedProperties extends Properties {

    /**
     * Reads a property list (key and element pairs) from the input byte stream.
     * 
     * <p>Behaves exactly as {@link java.util.Properties#load(java.io.InputStream) }
     * with the exception that trailing whitespace is trimmed from property values
     * if <tt>inStream</tt> is an instance of <tt>FileInputStream</tt>.
     * 
     * @see java.util.Properties#load(java.io.InputStream) 
     * @param inStream the input stream.
     * @throws IOException if an error occurred when reading from the input stream.
     */
    @Override
    public void load(InputStream inStream) throws IOException {
        if (inStream instanceof FileInputStream) {
            // First read into temporary props using the standard way
            Properties tempProps = new Properties();
            tempProps.load(inStream);
            // Now trim and put into target
            trimAndLoad(tempProps);
        } else {
            super.load(inStream);
        }
    }

    /**
     * Reads a property list (key and element pairs) from the input character stream in a simple line-oriented format. 
     * 
     * <p>Behaves exactly as {@link java.util.Properties#load(java.io.Reader)}
     * with the exception that trailing whitespace is trimmed on property values
     * if <tt>reader</tt> is an instance of <tt>FileReader</tt>.
     * 
     * @see java.util.Properties#load(java.io.Reader) }
     * @param reader the input character stream.
     * @throws IOException if an error occurred when reading from the input stream.
     */
    @Override
    public void load(Reader reader) throws IOException {
        if (reader instanceof FileReader) {
            // First read into temporary props using the standard way
            Properties tempProps = new Properties();
            tempProps.load(reader);
            // Now trim and put into target
            trimAndLoad(tempProps);
        } else {
            super.load(reader);
        }
    }

    private void trimAndLoad(Properties p) {
        for (Entry<Object, Object> entry : p.entrySet()) {
            if (entry.getValue() instanceof String) {
                put(entry.getKey(), trimTrailing((String) entry.getValue()));
            } else {
                put(entry.getKey(), entry.getValue());
            }
        }
    }

    /**
     * Trims trailing space or tabs from a string.
     *
     * @param str
     * @return
     */
    public static String trimTrailing(String str) {
        if (str != null) {
            // read str from tail until char is no longer whitespace
            for (int i = str.length() - 1; i >= 0; i--) {
                if ((str.charAt(i) != ' ') && (str.charAt(i) != '\t')) {
                    return str.substring(0, i + 1);
                }
            }
        }
        return str;
    }
}