{"id":10196,"date":"2015-01-31T17:17:54","date_gmt":"2015-01-31T09:17:54","guid":{"rendered":"https:\/\/lifeparty.idv.tw\/blog\/?p=10196"},"modified":"2015-02-02T10:20:21","modified_gmt":"2015-02-02T02:20:21","slug":"%e7%94%a8-java-%e5%af%a6%e4%bd%9c%e8%aa%9e%e8%a8%80%e6%95%b4%e5%90%88%e6%9f%a5%e8%a9%a2%e5%8a%9f%e8%83%bd","status":"publish","type":"post","link":"https:\/\/lifeparty.idv.tw\/blog\/archives\/10196","title":{"rendered":"\u7528 Java \u5be6\u4f5c\u8a9e\u8a00\u6574\u5408\u67e5\u8a62\u529f\u80fd"},"content":{"rendered":"

\u8a9e\u8a00\u6574\u5408\u67e5\u8a62<\/a>\uff08LINQ\uff09\u662f\u975e\u5e38\u6709\u7528\u7684\u8a2d\u8a08\u6982\u5ff5\uff0c\u5b83\u626d\u8f49\u6211\u5011\u904e\u53bb\u7528\u6307\u4ee4\u5f0f\u7de8\u7a0b<\/a>\u7684\u7fd2\u6163\uff0c\u8f49\u800c\u4ee5\u5ba3\u544a\u5f0f\u7de8\u7a0b<\/a>\u7684\u8a2d\u8a08\u5178\u7bc4\uff0c\u8b93\u7a0b\u5f0f\u78bc\u8b8a\u5f97\u7c21\u6f54\uff0c\u4e5f\u63d0\u9ad8\u8a2d\u8a08\u7684\u62bd\u8c61\u80fd\u529b\u3002\u5c24\u5176\u662f\u5c0d\u65bc\u8ff4\u5708\u7576\u4e2d\u4e00\u518d\u51fa\u73fe\u985e\u4f3c\u7684\u689d\u4ef6\u5224\u65b7\uff0c\u537b\u82e6\u65bc\u8ff4\u5708\u7684\u7279\u6027\u8b93\u6211\u5011\u6c92\u6709\u5f88\u597d\u7684\u7b56\u7565\u4f86\u5c07\u8b8a\u52d5\u7684\u90e8\u5206\u5c01\u88dd\u8d77\u4f86\uff0c\u53ea\u80fd\u4efb\u7531\u8b93\u7a0b\u5f0f\u78bc\u56e0\u61c9\u9700\u6c42\u6539\u8b8a\u800c\u65e5\u8da8\u8907\u96dc\uff0c\u8b93\u958b\u767c\u53ca\u7dad\u8b77\u7a0b\u5f0f\u6108\u4f86\u6108\u56f0\u96e3\u7684\u6642\u5019\u3002\u4f46\u5982\u679c\u6211\u5011\u80fd\u5920\u628a\u6307\u4ee4\u5f0f\u7de8\u7a0b\u7684\u958b\u767c\u6163\u4f8b\u63db\u6210\u5ba3\u544a\u5f0f\u7de8\u7a0b\u7684\u601d\u7dad\u6a21\u5f0f<\/a>\uff0c\u6211\u5011\u5c31\u6703\u767c\u73fe\u554f\u984c\u5c07\u8b8a\u5f97\u5f88\u7c21\u55ae\u3002<\/p>\n

\u5982\u540c .NET Framework \u652f\u63f4 LINQ \u7684\u67e5\u8a62\u8a9e\u53e5\u53ef\u4ee5\u62bd\u63db\u67e5\u8a62\u7684\u689d\u4ef6\u5f0f\uff08\u900f\u904e where() \u65b9\u6cd5\uff09\u548c\u67e5\u8a62\u7d50\u679c\u7684\u5c0d\u61c9\uff08\u900f\u904e select()\u3001groupBy()\u7b49\u65b9\u6cd5\uff09\uff0c\u5176\u5be6\u5728 Java 1.6 \u6211\u5011\u4e5f\u53ef\u4ee5\u7528\u76f8\u540c\u7684\u8a2d\u8a08\u6982\u5ff5\u5be6\u4f5c\u8a9e\u8a00\u6574\u5408\u529f\u80fd\u3002\u672c\u4f86\u540c\u4eba\u4e00\u76f4\u8a8d\u70ba\u5be6\u4f5c\u5b83\u61c9\u8a72\u6703\u5f88\u8907\u96dc\uff0c\u4f46\u5be6\u969b\u52d5\u624b\u5f8c\u4f86\u767c\u73fe\uff0c\u5be6\u4f5c\u5b83\u6bd4\u60f3\u50cf\u4e2d\u7684\u4f86\u7684\u7c21\u55ae\uff0c\u4e5f\u53ea\u662f\u904b\u7528\u5ef6\u9072\u904b\u7b97\u7684\u89c0\u5ff5\u548c\u4e00\u4e9b\u8a2d\u8a08\u6a23\u5f0f\u7684\u624b\u6cd5\u5c31\u80fd\u5920\u5f88\u8f15\u6613\u7684\u5be6\u73fe\u4e86\u3002<\/p>\n

\u6211\u5011\u5148\u4f86\u770b\u5982\u4f55\u4f7f\u7528\u8a9e\u8a00\u6574\u5408\u67e5\u8a62\uff0c\u540c\u4eba\u628a\u5be6\u4f5c\u7684\u76ee\u6a19\u5b9a\u5728\u96c6\u5408\u7684\u67e5\u8a62\uff0c\u4e5f\u5c31\u662f CollectionQuery\uff0c\u4f7f\u7528\u5b83\u7684\u6e2c\u8a66\u6848\u4f8b\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n

public class CollectionQueryTest {\r\n\r\n    private List<MyObj> myObjList = Arrays.asList(new MyObj[]{\r\n        new MyObj(123, "a", "abc"),\r\n        new MyObj(246, "a", "ace"),\r\n        new MyObj(369, "b", "bbb"),\r\n        new MyObj(456, "x", "xyz")\r\n    });\r\n\r\n    @Test\r\n    public void testSelect() {\r\n        List<MyResult> result = CollectionQuery.from(myObjList)\r\n                .where(new Expression<MyObj, Boolean>() {\r\n                    @Override\r\n                    public Boolean evaluate(MyObj myObj) {\r\n                        return !"x".equals(myObj.getKind());\r\n                    }\r\n                })\r\n                .select(new Expression<MyObj, MyResult>() {\r\n                    @Override\r\n                    public MyResult evaluate(MyObj myObj) {\r\n                        MyResult myResult = new MyResult(myObj.getKind() + ":"\r\n                                + myObj.getName());\r\n\r\n                        return myResult;\r\n                    }\r\n                })\r\n                .getResult();\r\n\r\n        Assert.assertEquals(3, result.size());\r\n        Assert.assertEquals("a:abc", result.get(0).getResultStr());\r\n        Assert.assertEquals("a:ace", result.get(1).getResultStr());\r\n        Assert.assertEquals("b:bbb", result.get(2).getResultStr());\r\n    }\r\n\r\n    @Test\r\n    public void testGrouping() {\r\n        List<MyResult> result =\r\n                CollectionQuery.from(myObjList)\r\n                .groupBy(new Expression<MyObj, String>() {\r\n                    @Override\r\n                    public String evaluate(MyObj myObj) {\r\n                        return myObj.getKind();\r\n                    }\r\n                }, new Expression<MyObj, String>() {\r\n\r\n                    @Override\r\n                    public String evaluate(MyObj myObj) {\r\n                        return myObj.getName();\r\n                    }\r\n                }\r\n                )\r\n                .select(new Expression<CollectionGrouping<String, String>, MyResult>() {\r\n\r\n                    @Override\r\n                    public MyResult evaluate(CollectionGrouping<String, String> myGrouping) {\r\n                        StringBuilder sb = new StringBuilder()\r\n                                .append(myGrouping.getKey());\r\n                        boolean initiated = false;\r\n                        for (Iterator<String> iterator = myGrouping.getElementsIterator();\r\n                                iterator.hasNext();) {\r\n                            if (initiated) {\r\n                                sb.append(',');\r\n                            }\r\n                            else {\r\n                                sb.append(':');\r\n                                initiated = true;\r\n                            }\r\n                            sb.append(iterator.next());\r\n                        }\r\n                        return new MyResult(sb.toString());\r\n                    }\r\n\r\n                })\r\n                .getResult();\r\n\r\n        Assert.assertEquals(3, result.size());\r\n\r\n        Assert.assertEquals("a:abc,ace", result.get(0).getResultStr());\r\n        Assert.assertEquals("b:bbb", result.get(1).getResultStr());\r\n        Assert.assertEquals("x:xyz", result.get(2).getResultStr());\r\n    }\r\n}<\/pre>\n
\u6e2c\u8a66\u6848\u4f8b\u7528\u5230\u7684 MyObj \u53ca MyResult \u5247\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
class MyObj {\r\n\r\n    private int id;\r\n\r\n    private String kind;\r\n\r\n    private String name;\r\n\r\n    MyObj(int id, String kind, String name) {\r\n        this.id = id;\r\n        this.kind = kind;\r\n        this.name = name;\r\n    }\r\n\r\n    public int getId() {\r\n        return id;\r\n    }\r\n\r\n    public String getKind() {\r\n        return kind;\r\n    }\r\n\r\n    public String getName() {\r\n        return name;\r\n    }\r\n\r\n}\r\n\r\npublic class MyResult {\r\n\r\n    private String resultStr;\r\n\r\n    MyResult(String resultStr) {\r\n        this.resultStr = resultStr;\r\n    }\r\n\r\n    public String getResultStr() {\r\n        return resultStr;\r\n    }    \r\n\r\n}<\/pre>\n
\u8981\u8b93\u6e2c\u8a66\u6848\u4f8b\u901a\u904e\uff0c\u6211\u5011\u8981\u5148\u5b9a\u7fa9 CollectionQuery \u985e\u5225\uff0c\u5728\u9019\u908a\u540c\u4eba\u4f7f\u7528 Composite Pattern<\/a>\u3002\u56e0\u70ba\u67e5\u8a62\u904e\u7a0b\u8981\u8655\u7406\u96c6\u5408\u4e2d\u7684\u5143\u7d20\uff0c\u6211\u662f\u63a1\u7528\u5ef6\u9072\u904b\u7b97\u7684\u4f5c\u6cd5\uff0c\u4e5f\u5c31\u662f\u6703\u628a\u67d0\u7a2e\u8cc7\u6599\u985e\u5225\u7684\u5143\u7d20\u8f49\u63db\u6210\u4e00\u5143\u8868\u9054\u5f0f Expression<T, R>\uff0c\u5176\u4e2d T \u4ee3\u8868\u904b\u7b97\u5f0f\u7684\u53c3\u6578\u578b\u614b\uff0c\u800c R \u4ee3\u8868\u904b\u7b97\u7d50\u679c\u7684\u578b\u614b\u3002\u53ef\u60f3\u800c\u77e5\uff0cCollectionQuery \u5c07\u6703\u4e00\u500b\u5957\u4e00\u500b\uff0c\u4e5f\u5c31\u662f\u6211\u5011\u53ef\u80fd\u6703\u7528 select() \u8f49\u63db\u96c6\u5408\u5167\u7684\u5143\u7d20\uff0c\u6216\u662f\u7528 groupBy() \u6b78\u985e\u96c6\u5408\u5167\u7684\u5143\u7d20\uff1b\u67e5\u8a62\u7684\u6bcf\u6b21\u64cd\u4f5c\u4e2d\u90fd\u6703\u8907\u5408\u6211\u5011\u7684 CollectionQuery\uff0c\u65bc\u662f CollectionQuery \u7684\u5b9a\u7fa9\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
public abstract class CollectionQuery<T> {\r\n\r\n    private List<Expression<T, Boolean>> predicates\r\n            = new ArrayList<Expression<T, Boolean>>();\r\n\r\n    public static <R> CollectionQuery<R> from(List<R> list) {\r\n        return new ListQuery(list);\r\n    }\r\n\r\n    public CollectionQuery<T> where(Expression<T, Boolean> predicate) {\r\n        predicates.add(predicate);\r\n        return this;\r\n    }\r\n\r\n    public <R> CollectionQuery<R> select(Expression<T, R> projection) {\r\n        return new FunctorCollectionQuery<T, R>(projection, this);\r\n    }\r\n\r\n    public <K, R> CollectionQuery<CollectionGrouping<K, R>> groupBy(\r\n            Expression<T, K> keyProjection, Expression<T, R> valueProjection) {\r\n        return new GroupingCollectionQuery<T, K, R>(keyProjection,\r\n                valueProjection, this);\r\n    }\r\n\r\n    protected abstract Iterator<T> getIterator();\r\n\r\n    public List<T> getResult() {\r\n        List<T> result = new ArrayList<T>();       \r\n\r\n        for (Iterator<T> iterator = getIterator();iterator.hasNext();) {\r\n            T t = iterator.next();\r\n            boolean broken = false;\r\n            for (Expression<T, Boolean> predicate : predicates) {\r\n                if (!predicate.evaluate(t)) {\r\n                    broken = true;\r\n                    break;\r\n                }\r\n            }\r\n\r\n            if (!broken) {\r\n                result.add(t);\r\n            }\r\n        }\r\n        return result;\r\n    }\r\n\r\n}<\/pre>\n
\u6700\u521d\u7684 CollectionQuery \u662f\u7531 CollectionQuery \u7684\u975c\u614b factory method from() \u6240\u7522\u751f\uff0c\u723e\u5f8c\u5c0d CollectionQuery \u9032\u884c\u64cd\u4f5c\u90fd\u6703\u50b3\u56de\u4e00\u500b CollectionQuery \u4ee5\u5229\u9023\u7e8c\u67e5\u8a62\u64cd\u4f5c\uff0c\u5982\u679c\u64cd\u4f5c\u53ea\u662f\u50cf where() \u7684\u7be9\u9078\u8cc7\u6599\uff0c\u90a3\u9ebc\u6211\u5011\u53ea\u662f\u628a\u7be9\u9078\u8cc7\u6599\u7684 predicate \u52a0\u5165\u6574\u500b predicates \u7576\u4e2d\uff0c\u518d\u56de\u50b3\u6574\u500b CollectionQuery \u7684\u5be6\u9ad4\u3002\u4ee5 Functional Programming \u7684\u89c0\u5ff5\u4f86\u8aaa\uff0c\u56de\u50b3\u7684 CollectionQuery \u5df2\u7d93\u4e0d\u662f\u539f\u4f86\u7684 CollectionQuery\uff0c\u53ea\u662f\u7ad9\u5728\u5be6\u4f5c\u7684\u8003\u91cf\uff0c\u6211\u5011\u6c92\u6709\u5fc5\u8981\u518d new \u4e00\u500b\u65b0\u7684 CollectionQuery \u5be6\u9ad4\u9020\u6210\u8a18\u61b6\u9ad4\u7684\u6d6a\u8cbb\u3002<\/p>\n
\u7136\u800c\uff0c\u81f3\u65bc select() \u548c groupBy() \u64cd\u4f5c\uff0c\u5247\u56de\u50b3\u7684 CollectionQuery \u5247\u9700\u8981\u5efa\u69cb\u65b0\u7684 FunctorCollectionQuery\u3001\u4ee5\u53ca GroupingCollectionQuery\uff0c\u6240\u4ee5\u5b83\u5011\u5fc5\u9808\u7e7c\u627f\u81ea CollectionQuery\uff0c\u4e26\u4e14\u5be6\u4f5c getIterator() \u4f9b getResult() \u5faa\u5e8f\u8655\u7406 Collection \u7684\u5167\u5b58\u8cc7\u6599\u6216\u8868\u9054\u5f0f\u3002\u9650\u65bc\u6587\u7ae0\u7684\u7bc7\u8f3b\u6709\u9650\uff0c\u5728\u9019\u908a\u6211\u53ea\u5217\u51fa\u8f03\u8907\u96dc\u7684 GroupingCollectionQuery \u4e4b getIterator() \u5be6\u4f5c\uff0c\u76f8\u4fe1\u4ee5\u6b64\u985e\u63a8\uff0c\u66f4\u7c21\u55ae\u7684 FunctorCollectionQuery \u7684 getIterator() \u5be6\u4f5c\u4e5f\u662f\u4e00\u9ede\u90fd\u4e0d\u56f0\u96e3\u7684\uff1a<\/p>\n
    @Override\r\n    protected Iterator<CollectionGrouping<K, E>> getIterator() {\r\n        Map<K, CollectionGrouping<K, E>> groupings =\r\n                new TreeMap<K, CollectionGrouping<K, E>>();\r\n\r\n        for (T t : elementsQuery.getResult()) {\r\n            K key = keyProjection.evaluate(t);\r\n            CollectionGrouping<K, E> grouping = groupings.get(key);\r\n            if (null == grouping) {\r\n                grouping = new ListElementsCollectionGrouping<K, E>(key);\r\n                groupings.put(key, grouping);\r\n            }\r\n            E element = elementProjection.evaluate(t);\r\n            grouping.add(element);\r\n        }\r\n\r\n        return new ArrayList<CollectionGrouping<K, E>>(groupings.values())\r\n                .iterator();\r\n    }<\/pre>\n
\u5728\u9019\u908a\u9084\u9700\u8981\u4ea4\u5f85\u4e00\u4e0b CollectionGrouping<K, E>\uff0c\u5b83\u662f\u7528\u4f86\u8868\u793a\u96c6\u5408\u5206\u7fa4\u7684\u754c\u9762\uff1b\u5176\u4e2d K \u4ee3\u8868\u9375\u503c\u985e\u5225\uff0cE \u4ee3\u8868\u7fa4\u5167\u5143\u7d20\u985e\u5225\u3002\u5b83\u9084\u63d0\u4f9b accumulate() \u4f9b\u50b3\u5165 Accumlator<K, E, R> \u4f86\u9032\u884c\u7d2f\u7a4d\u7684\u64cd\u4f5c\uff0cCollectionGrouping<K, E> \u53ca Accumlator<K, E, R> \u7684\u5b9a\u7fa9\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
public interface CollectionGrouping<K, E> {\r\n\r\n    public K getKey();\r\n\r\n    public Iterator<E> getElementsIterator();\r\n\r\n    public void add(E result);\r\n\r\n    public long getCount();\r\n\r\n    public E max(Comparator<E> comparator);\r\n\r\n    public E min(Comparator<E> comparator);\r\n\r\n    public <R> R accumulate(GroupingAccumulator<K, E, R> accumulator);\r\n\r\n}\r\n\r\npublic interface GroupingAccumulator<K, E, R> {\r\n    public void accumulate(K key, E element);\r\n\r\n    public R getResult();\r\n\r\n}<\/pre>\n
\u4ee5\u4e0a\uff0c\u4fbf\u662f\u540c\u4eba\u7528 Java \u5be6\u4f5c\u8a9e\u8a00\u6574\u5408\u67e5\u8a62\u529f\u80fd\u7684\u7d93\u9a57\u5206\u4eab\u3002\u672c\u4f86\u6211\u4ee5\u524d\u90fd\u7528 Collections \u548c CollectionUtils \u4f86\u8655\u7406\u96c6\u5408\u4e2d\u5167\u5b58\u7684\u5143\u7d20\uff0c\u4f46\u5b83\u5011\u7684\u529f\u80fd\u90fd\u6975\u5176\u6709\u9650\u3002\u4e5f\u8a31\u5728\u6307\u4ee4\u5f0f\u7de8\u7a0b\u7684\u9818\u57df\u7576\u4e2d\uff0c\u5b83\u5011\u5df2\u7d93\u5f88\u5920\u7528\u4e86\uff0c\u4f46\u5728\u5ba3\u544a\u5f0f\u7de8\u7a0b\u7684\u9818\u57df\u7576\u4e2d\uff0c\u4f7f\u7528\u5b83\u5011\u5be6\u5728\u662f\u7565\u611f\u4e0d\u8db3\u3002\u96d6\u7136\u6211\u73fe\u5728\u5de5\u4f5c\u4e0a\u9084\u6c92\u7528\u5230 Java 8\uff0c\u4f46\u6c92\u6709 lambda expression<\/a> \u4ecd\u7136\u53ef\u4ee5\u7528\u533f\u540d\u985e\u5225\u7684\u65b9\u5f0f\u4f86\u9054\u5230\u533f\u540d\u51fd\u5f0f\u7684\u6548\u679c\uff0c\u5176\u5be6\u4e5f\u662f\u68d2\u7684\u5440\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
\u8a9e\u8a00\u6574\u5408\u67e5\u8a62\uff08LINQ\uff09\u662f\u975e\u5e38\u6709\u7528\u7684\u8a2d\u8a08\u6982\u5ff5\uff0c\u5b83\u626d\u8f49\u6211\u5011\u904e\u53bb\u7528\u6307\u4ee4\u5f0f\u7de8\u7a0b\u7684\u7fd2\u6163\uff0c … \u95b1\u8b80\u5168\u6587 →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[29,37,43,19,3],"tags":[],"class_list":["post-10196","post","type-post","status-publish","format-standard","hentry","category-29","category-37","category-43","category-19","category-3"],"_links":{"self":[{"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/posts\/10196","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/comments?post=10196"}],"version-history":[{"count":28,"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/posts\/10196\/revisions"}],"predecessor-version":[{"id":10225,"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/posts\/10196\/revisions\/10225"}],"wp:attachment":[{"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/media?parent=10196"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/categories?post=10196"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lifeparty.idv.tw\/blog\/wp-json\/wp\/v2\/tags?post=10196"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}