Converts command-line switches of the form --key1=value1 --key2=value2 into a Properties object.

Description

Demo Code

// Copyright 2008 Google Inc. All Rights Reserved.
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.HashSet;
import java.util.Properties;
import java.util.Set;

public class Main{
    private static final int SMALLEST_POSSIBLE_ALIASED_STRING = 4;
    private static final String VAR_START = "${";
    private static final String VAR_END = "}";
    private static final String ARG_PREFIX = "--";
    /**//w w w .j a va2 s. c  o m
     * Converts command-line switches of the form --key1=value1 --key2=value2 into
     * a Properties object. A Switch of the form --props=/path/to/some/file.properties
     * gets special treatment; the properties file is loaded and added to the set
     * of command-line switches (command-line taking precedence over properties file)
     * and a new property called "basedir" is added which is the directory containing
     * the properties file.
     *
     * @param args
     * @return
     * @throws IOException
     */
    public static Properties getPropertiesFromCommandLine(String[] args)
            throws IOException {
        Properties props = toProperties(args);
        // now to add our current working directory as a property
        props.setProperty("cwd", System.getProperty("user.dir"));
        File externalPropsFile = PropertiesUtil.getFile(props, "props");
        if (externalPropsFile != null) {
            Properties externalProps = PropertiesUtil
                    .readProperties(externalPropsFile);
            // add the property "basedir" just like ant does
            externalProps.setProperty("basedir", externalPropsFile
                    .getParentFile().toString());
            // command-line properties override external properties file
            externalProps.putAll(props);
            props = externalProps;
        }
        return props;
    }
    /**
     * Converts command-line switches of the form --key1=value1 --key2=value2 into
     * a Properties object.
     *
     * @param args the arguments to parse
     * @return the parsed properties
     */
    public static Properties toProperties(String[] args) {
        Properties props = new Properties();
        if (args != null) {
            for (String arg : args) {
                if (arg.startsWith(ARG_PREFIX)) {
                    arg = arg.substring(ARG_PREFIX.length());
                    int eq = arg.indexOf('=');
                    if (eq > 0) {
                        String key = arg.substring(0, eq);
                        String value = arg.substring(eq + 1);
                        props.setProperty(key, value);
                    }
                }
            }
        }
        return props;
    }
    /**
     * Get a canonical file property using aliasing.
     *
     * @param props the properties object to use
     * @param name the (possibly aliased) property name to use
     * @return null if the property was not found
     * @throws IOException if there is a problem getting the canonical form
     * of the file.
     */
    public static File getFile(Properties props, String name)
            throws IOException {
        String fileAsString = getAliasedProperty(props, name, null);
        if (fileAsString == null) {
            return null;
        }
        if (fileAsString.indexOf("${") >= 0
                && fileAsString.indexOf("}") >= 0) {
            throw new IOException("Cannot resolve '" + fileAsString + "'");
        }
        File file = new File(fileAsString);
        return file.getCanonicalFile();
    }
    /**
     * Reads a properties file.
     *
     * @param f the properties file
     * @return a Properties object containing the parse properties
     */
    public static Properties readProperties(File f) throws IOException {
        Properties props = new Properties();
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(f);
            props.load(fis);
        } finally {
            if (fis != null) {
                fis.close();
            }
        }
        return props;
    }
    /**
     * Retrieves an "aliased" property from a Properties object. For example, a
     * Properties object containing: host=localhost url=http://${host}/index.html
     *
     * would return "http://localhost/index.html" from a call to
     * getAliasedProperty(props, "url", null)
     */
    public static String getAliasedProperty(Properties props, String key,
            String def) {
        return getAliasedProperty(props, key, def, new HashSet<String>());
    }
    private static String getAliasedProperty(Properties props, String key,
            String def, Set<String> keysToIgnore) {
        String value = props.getProperty(key);
        if (value == null) {
            return def;
        }
        keysToIgnore.add(key);
        String translatedValue = translateString(value, props, keysToIgnore);
        keysToIgnore.remove(key);
        return translatedValue;
    }
    private static String translateString(String value, Properties props,
            Set<String> keysToIgnore) {
        int n = value.length();
        if (n < SMALLEST_POSSIBLE_ALIASED_STRING) {
            // if value is less characters than "${x}" then no translation is needed
            return value;
        }
        int startVarIndex = value.indexOf(VAR_START);
        if (startVarIndex == -1) {
            return value; // nothing to translate
        }
        int endVarIndex = findMatchingBrace(value, startVarIndex + 1);
        if (endVarIndex == -1) {
            return value; // nothing to translate
        }

        StringBuffer sb = new StringBuffer();
        sb.append(value.substring(0, startVarIndex));
        String aliasedKey = value.substring(
                startVarIndex + VAR_START.length(), endVarIndex);
        String aliasedKeyDefaultValue = VAR_START + aliasedKey + VAR_END;
        if (keysToIgnore.contains(aliasedKey)) {
            sb.append(aliasedKeyDefaultValue);
        } else {
            sb.append(getAliasedProperty(props, aliasedKey,
                    aliasedKeyDefaultValue, keysToIgnore));
        }
        sb.append(translateString(value.substring(endVarIndex + 1), props,
                keysToIgnore));
        return sb.toString();
    }
}
Converts command-line switches of the form --key1=value1 --key2=value2 into a Properties object. - Java java.util

Description

Demo Code

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