java/src/main/com/google/apphosting/utils/config/YamlUtils.java

   1 // Copyright 2010 Google Inc. All Rights Reserved.
   2
   3 package com.google.apphosting.utils.config;
   4
   5 import net.sourceforge.yamlbeans.YamlException;
   6 import net.sourceforge.yamlbeans.YamlReader;
   7
   8 import java.util.HashMap;
   9 import java.util.Map;
  10 import java.util.Map.Entry;
  11 import java.util.regex.Pattern;
  12
  13 /**
  14  * Helper methods for parsing YAML files.
  15  *
  16  */
  17 public class YamlUtils {
  18
  19   static final Pattern TRUE_PATTERN =
  20       Pattern.compile("y|Y|yes|Yes|YES|true|True|TRUE|on|On|ON");
  21   static final Pattern FALSE_PATTERN =
  22       Pattern.compile("n|N|no|No|NO|false|False|FALSE|off|Off|OFF");
  23
  24   private static final String RESERVED_URL =
  25     "The URL '%s' is reserved and cannot be used.";
  26
  27   private YamlUtils() { }
  28
  29   /**
  30    * Parse a YAML !!bool type. YamlBeans only supports "true" or "false".
  31    *
  32    * @throws AppEngineConfigException
  33    */
  34   static boolean parseBoolean(String value) {
  35     if (TRUE_PATTERN.matcher(value).matches()) {
  36       return true;
  37     } else if (FALSE_PATTERN.matcher(value).matches()) {
  38       return false;
  39     }
  40     throw new AppEngineConfigException("Invalid boolean value '" + value + "'.");
  41   }
  42
  43   /**
  44    * Check that a URL is not one of the reserved URLs according to
  45    * http://code.google.com/appengine/docs/java/configyaml/appconfig_yaml.html#Reserved_URLs
  46    *
  47    * @throws AppEngineConfigException
  48    */
  49   static void validateUrl(String url) {
  50     if (url.equals("/form")) {
  51       throw new AppEngineConfigException(String.format(RESERVED_URL, url));
  52     }
  53   }
  54
  55   /**
  56    * Parse the data into YAML.
  57    *
  58    * @param data The text to parse as YAML.
  59    * @return The YAML data as a Map.
  60    * @throws AppEngineConfigException Throws when the underlying Yaml library
  61    * detects bad data of when the data does not parse to a Map.
  62    */
  63   @SuppressWarnings("unchecked")
  64   public static Map<String, Object> genericParse(String data)
  65       throws AppEngineConfigException {
  66     try {
  67       YamlReader reader = new YamlReader(data);
  68       return reader.read(Map.class);
  69     } catch (YamlException exc) {
  70       throw new AppEngineConfigException("Invalid YAML data: " + data, exc);
  71     }
  72   }
  73
  74   /**
  75    * A utility class that encapsulates conversion between different
  76    * types of objects.
  77    */
  78   public static interface ObjectConverter<T> {
  79     T convert(Object obj) throws Exception;
  80   }
  81
  82   /**
  83    * Parses the data into YAML and converts the map values.
  84    *
  85    * @param data The text to parse as YAML.
  86    * @param converter A converter for updating the values of the Map from
  87    * the type returned from the underlying Yaml library to the expected type.
  88    * @return The YAML data as a Map.
  89    * @throws AppEngineConfigException Throws when the underlying Yaml library
  90    * detects bad data or when the data does not parse to a Map. Also all
  91    * Exceptions from ObjectConverted are encapsulated in an
  92    * AppEngineConfigException.
  93    */
  94   public static <T> Map<String, T> genericParse(String data,
  95       ObjectConverter<T> converter) throws AppEngineConfigException {
  96     try {
  97       Map<String, T> yaml = new HashMap<String, T>();
  98       for (Entry<String, Object> entry : genericParse(data).entrySet()) {
  99         yaml.put(entry.getKey(), converter.convert(entry.getValue()));
 100       }
 101       return yaml;
 102     } catch (Exception exc) {
 103       throw new AppEngineConfigException(exc);
 104     }
 105   }
 106 }