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1   /*
2    * Copyright 2006-2007 the original author or authors.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package org.springframework.batch.repeat.exception;
18  
19  import java.util.HashMap;
20  import java.util.Map;
21  import java.util.Map.Entry;
22  
23  import org.apache.commons.logging.Log;
24  import org.apache.commons.logging.LogFactory;
25  import org.springframework.classify.Classifier;
26  import org.springframework.classify.SubclassClassifier;
27  import org.springframework.batch.repeat.RepeatContext;
28  import org.springframework.batch.repeat.context.RepeatContextCounter;
29  import org.springframework.util.ObjectUtils;
30  
31  /**
32   * Implementation of {@link ExceptionHandler} that rethrows when exceptions of a
33   * given type reach a threshold. Requires an {@link Classifier} that maps
34   * exception types to unique keys, and also a map from those keys to threshold
35   * values (Integer type).
36   * 
37   * @author Dave Syer
38   * 
39   */
40  public class RethrowOnThresholdExceptionHandler implements ExceptionHandler {
41  
42  	protected static final IntegerHolder ZERO = new IntegerHolder(0);
43  
44  	protected final Log logger = LogFactory.getLog(RethrowOnThresholdExceptionHandler.class);
45  
46  	private Classifier<? super Throwable, IntegerHolder> exceptionClassifier = new Classifier<Throwable, IntegerHolder>() {
47          @Override
48  		public RethrowOnThresholdExceptionHandler.IntegerHolder classify(Throwable classifiable) {
49  			return ZERO;
50  		}
51  	};
52  
53  	private boolean useParent = false;
54  
55  	/**
56  	 * Flag to indicate the the exception counters should be shared between
57  	 * sibling contexts in a nested batch. Default is false.
58  	 * 
59  	 * @param useParent true if the parent context should be used to store the
60  	 * counters.
61  	 */
62  	public void setUseParent(boolean useParent) {
63  		this.useParent = useParent;
64  	}
65  
66  	/**
67  	 * Set up the exception handler. Creates a default exception handler and
68  	 * threshold that maps all exceptions to a threshold of 0 - all exceptions
69  	 * are rethrown by default.
70  	 */
71  	public RethrowOnThresholdExceptionHandler() {
72  		super();
73  	}
74  
75  	/**
76  	 * A map from exception classes to a threshold value of type Integer.
77  	 * 
78  	 * @param thresholds the threshold value map.
79  	 */
80  	public void setThresholds(Map<Class<? extends Throwable>, Integer> thresholds) {
81  		Map<Class<? extends Throwable>, IntegerHolder> typeMap = new HashMap<Class<? extends Throwable>, IntegerHolder>();
82  		for (Entry<Class<? extends Throwable>, Integer> entry : thresholds.entrySet()) {
83  			typeMap.put(entry.getKey(), new IntegerHolder(entry.getValue()));
84  		}
85  		exceptionClassifier = new SubclassClassifier<Throwable, IntegerHolder>(typeMap, ZERO);
86  	}
87  
88  	/**
89  	 * Classify the throwables and decide whether to re-throw based on the
90  	 * result. The context is used to accumulate the number of exceptions of the
91  	 * same type according to the classifier.
92  	 * 
93  	 * @throws Throwable
94  	 * @see ExceptionHandler#handleException(RepeatContext, Throwable)
95  	 */
96      @Override
97  	public void handleException(RepeatContext context, Throwable throwable) throws Throwable {
98  
99  		IntegerHolder key = exceptionClassifier.classify(throwable);
100 
101 		RepeatContextCounter counter = getCounter(context, key);
102 		counter.increment();
103 		int count = counter.getCount();
104 		int threshold = key.getValue();
105 		if (count > threshold) {
106 			throw throwable;
107 		}
108 
109 	}
110 
111 	private RepeatContextCounter getCounter(RepeatContext context, IntegerHolder key) {
112 		String attribute = RethrowOnThresholdExceptionHandler.class.getName() + "." + key;
113 		// Creates a new counter and stores it in the correct context:
114 		return new RepeatContextCounter(context, attribute, useParent);
115 	}
116 
117 	/**
118 	 * @author Dave Syer
119 	 * 
120 	 */
121 	private static class IntegerHolder {
122 
123 		private final int value;
124 
125 		/**
126 		 * @param value
127 		 */
128 		public IntegerHolder(int value) {
129 			this.value = value;
130 		}
131 
132 		/**
133 		 * Public getter for the value.
134 		 * @return the value
135 		 */
136 		public int getValue() {
137 			return value;
138 		}
139 
140 		/*
141 		 * (non-Javadoc)
142 		 * 
143 		 * @see java.lang.Object#toString()
144 		 */
145 		@Override
146 		public String toString() {
147 			return ObjectUtils.getIdentityHexString(this) + "." + value;
148 		}
149 
150 	}
151 
152 }