/tags/release-0.1-rc2/hive/external/ql/src/java/org/apache/hadoop/hive/ql/exec/DefaultUDFMethodResolver.java

 1/**
 2 * Licensed to the Apache Software Foundation (ASF) under one
 3 * or more contributor license agreements.  See the NOTICE file
 4 * distributed with this work for additional information
 5 * regarding copyright ownership.  The ASF licenses this file
 6 * to you under the Apache License, Version 2.0 (the
 7 * "License"); you may not use this file except in compliance
 8 * with the License.  You may obtain a copy of the License at
 9 *
10 *     http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18
19package org.apache.hadoop.hive.ql.exec;
20
21import java.lang.reflect.Method;
22import java.util.List;
23
24import org.apache.hadoop.hive.serde2.typeinfo.TypeInfo;
25
26/**
27 * The default UDF Method resolver. This resolver is used for resolving the UDF
28 * method that is to be used for evaluation given the list of the argument
29 * types. The getEvalMethod goes through all the evaluate methods and returns
30 * the one that matches the argument signature or is the closest match. Closest
31 * match is defined as the one that requires the least number of arguments to be
32 * converted. In case more than one matches are found, the method throws an
33 * ambiguous method exception.
34 */
35public class DefaultUDFMethodResolver implements UDFMethodResolver {
36
37  /**
38   * The class of the UDF.
39   */
40  private final Class<? extends UDF> udfClass;
41
42  /**
43   * Constructor. This constructor sets the resolver to be used for comparison
44   * operators. See {@link UDFMethodResolver}
45   */
46  public DefaultUDFMethodResolver(Class<? extends UDF> udfClass) {
47    this.udfClass = udfClass;
48  }
49
50  /**
51   * Gets the evaluate method for the UDF given the parameter types.
52   * 
53   * @param argClasses
54   *          The list of the argument types that need to matched with the
55   *          evaluate function signature.
56   */
57  @Override
58  public Method getEvalMethod(List<TypeInfo> argClasses) throws UDFArgumentException {
59    return FunctionRegistry.getMethodInternal(udfClass, "evaluate", false,
60        argClasses);
61  }
62}