java安全編碼指南之:堆污染Heap pollution

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"簡介"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"什麼是堆污染呢？堆污染是指當參數化類型變量引用的對象不是該參數化類型的對象時而發生的。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們知道在JDK5中，引入了泛型的概念，我們可以在創建集合類的時候，指定該集合類中應該存儲的對象類型。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果在指定類型的集合中，引用了不同的類型，那麼這種情況就叫做堆污染。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"產生堆污染的例子"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有同學可能會問了，既然JDK5引入了泛型，爲什麼還會出現堆污染呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這是一個好問題，讓我們看一個例子："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public void heapPollution1(){\n List normalList= Arrays.asList(\"www.flydean.com\",100);\n List integerList= normalList;\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子中，我們使用Arrays.asList創建了一個普通的List。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這個List中包含了int和String兩種類型，當我們將List賦值給List的時候，java編譯器並不會去判斷賦值List中的類型，integerList中包含了非Integer的元素，最終導致在使用的時候會出現錯誤。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"直接給List賦值不會進行類型檢查，那麼如果我們是直接向List中添加元素呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們看下下面的例子："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" private void addToList(List list, Object object){\n list.add(object);\n }\n\n @Test\n public void heapPollution2(){\n List integerList=new ArrayList<>();\n addToList(integerList,\"www.flydean.com\");\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子中，我們定義了一個addToList方法，這個方法的參數是一個普通的List，但是我們傳入了一個List。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"結果，我們發現list.add方法並沒有進行參數類型校驗。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子該怎麼修改呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們需要在addToList方法的List參數中，也添加上類型校驗："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" private void addToList(List list, Object object){\n list.add(object);\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果addToList是一個非常通用的方法怎麼辦呢？在addToList的參數中添加參數類型是現實的。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這個時候，我們可以考慮使用Collections.checkedList方法來將輸入的List轉換成爲一個checkedList，從而只接收特定類型的元素。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" public void heapPollutionRight(){\n List integerList=new ArrayList<>();\n List checkedIntegerList= Collections.checkedList(integerList, Integer.class);\n addToList(checkedIntegerList,\"www.flydean.com\");\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"運行上面的代碼，我們將會得到下面的異常："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"java.lang.ClassCastException: Attempt to insert class java.lang.String element into collection with element type class java.lang.Integer\n"}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"更通用的例子"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面我們定義了一個addToList方法，因爲沒有做類型判斷，所以可能會出現堆污染的問題。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有沒有什麼辦法既可以通用，又可以避免堆污染呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當然有的，我們看下面的實現："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" private void addToList2(List list, T t) {\n list.add(t);\n }\n\n public void heapPollutionRight2(T element){\n List list = new ArrayList<>();\n addToList2(list,element);\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子中，我們在addToList方法中定義了一個參數類型T，通過這樣，我們保證了List中的元素類型的一致性。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"可變參數"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"事實上，方法參數可以是可變的，我們考慮下面的例子："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":" private void addToList3(List... listArray){\n Object[] objectArray = listArray;\n objectArray[0]= Arrays.asList(\"www.flydean.com\");\n for(List integerList: listArray){\n for(Integer element: integerList){\n System.out.println(element);\n }\n }\n }\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子中我們的參數是一個List的數組，雖然List中的元素類型固定了，但是我們可以重新賦值給參數數組，從而實際上修改掉參數類型。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果上面addToList3的方法參數修改爲下面的方式，就不會出現問題了："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"private void addToList4(List> listArray){\n\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這種情況下，List的類型是固定的，我們無法通過重新賦值的方式來修改它。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文的例子："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://github.com/ddean2009/learn-java-base-9-to-20/tree/master/security","title":null},"content":[{"type":"text","text":"learn-java-base-9-to-20/tree/master/security"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"本文已收錄於 "},{"type":"link","attrs":{"href":"http://www.flydean.com/java-security-code-line-heap-pollution/","title":null},"content":[{"type":"text","text":"http://www.flydean.com/java-security-code-line-heap-pollution/"}],"marks":[{"type":"italic"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"最通俗的解讀，最深刻的乾貨，最簡潔的教程，衆多你不知道的小技巧等你來發現！"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"歡迎關注我的公衆號:「程序那些事」,懂技術，更懂你！"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}