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Issue #109: Refact History object into a generic.
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103 changes: 103 additions & 0 deletions
103
src/main/java/com/github/mk23/jmxproxy/util/History.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,103 @@ | ||
| package com.github.mk23.jmxproxy.util; | ||
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| import java.util.ArrayList; | ||
| import java.util.Collections; | ||
| import java.util.List; | ||
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| /** | ||
| * <p>Fixed size historical attribute value store.</p> | ||
| * | ||
| * Saves an object into a fixed size round robin store. Allows clients to retreive latest | ||
| * value, a subset of latest values, or the full stored history of values. When number | ||
| * of stored values exceeds the fixed size of the store, the oldest values are overwritten. | ||
| * | ||
| * @param <T> type of objects held in this History. | ||
| * | ||
| * @since 2015-05-11 | ||
| * @author mk23 | ||
| * @version 3.3.2 | ||
| */ | ||
| public class History<T> { | ||
| private List<T> objects; | ||
| private int length; | ||
| private int pointer; | ||
| private boolean wrapped; | ||
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| /** | ||
| * <p>Default constructor.</p> | ||
| * | ||
| * Initializes the {@link Object} store {@link List} to the given history size. | ||
| * | ||
| * @param length number of {@link Object} values to keep in history. | ||
| */ | ||
| public History(final int length) { | ||
| this.length = length; | ||
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| pointer = -1; | ||
| objects = new ArrayList<T>(Collections.nCopies(length, (T) null)); | ||
| } | ||
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| /** | ||
| * <p>Adds a item to the store.</p> | ||
| * | ||
| * Adds a new item to the history store. If the number of items exceeds the size | ||
| * of the store, the oldest item is overwritten. | ||
| * | ||
| * @param item newest item to add to the store. | ||
| */ | ||
| public final void add(final T item) { | ||
| wrapped = ++pointer == length; | ||
| pointer = pointer % length; | ||
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| objects.set(pointer, item); | ||
| } | ||
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| /** | ||
| * <p>Gets the latest item from the history store.</p> | ||
| * | ||
| * Gets the latest single item from the history store. | ||
| * | ||
| * @return Latest item from the history store or null if empty. | ||
| */ | ||
| public final T getLast() { | ||
| return pointer < 0 ? null : objects.get(pointer % length); | ||
| } | ||
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| /** | ||
| * <p>Gets the full item history from the store.</p> | ||
| * | ||
| * Gets the full item history from the store as a {@link List}. | ||
| * | ||
| * @return {@link List} of the full history. May be empty if history has no items. | ||
| */ | ||
| public final List<T> get() { | ||
| return get(length); | ||
| } | ||
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| /** | ||
| * <p>Gets a limited item history from the store.</p> | ||
| * | ||
| * Gets a limited history from the store as a {@link List}, based | ||
| * on requested item count. If the specified count is less than 0 or greater than | ||
| * the number of entries, a full history is returned instead. | ||
| * | ||
| * @param limit number of items to retreive from the history store. | ||
| * | ||
| * @return {@link List} of the requested slice of history. May be empty if history has no items. | ||
| */ | ||
| public final List<T> get(final int limit) { | ||
| if (pointer < 0) { | ||
| return Collections.emptyList(); | ||
| } | ||
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| int head = pointer + length * Boolean.compare(wrapped, false); | ||
| int size = Math.min(limit > 0 ? limit : Integer.MAX_VALUE, Math.min((head + 1), length)); | ||
| List<T> rval = new ArrayList<T>(size); | ||
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| for (int i = 0; i < size; i++) { | ||
| rval.add(objects.get((head - i) % length)); | ||
| } | ||
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| return rval; | ||
| } | ||
| } |
4 changes: 4 additions & 0 deletions
4
src/main/java/com/github/mk23/jmxproxy/util/package-info.java
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,4 @@ | ||
| /** | ||
| * <p>Utility classes for the entire application.</p> | ||
| */ | ||
| package com.github.mk23.jmxproxy.util; |
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