java.lang.String无法强制转换为java.util.Map

Question

我是Java的新手，但不是编程的新手，所以作为我的第一个项目，我决定为工作中的某个人创建一个.txt-.csv解析器。 我读取了.txt文件中的每一行，并将其分成单独的地图，用于部分，子部分，子部分和子部分的内容。 然后将每个地图分配到其上方的地图（下面将详细介绍）。 我打印的一切都很好，但是当我尝试读取它时，我收到以下错误： "java.lang.String cannot be cast to java.util.Map" 。 该错误仅在代码运行后出现，而不是在编译时出现，也不出现在NetBeans IDE中。

我的地图是以下形式，每个对象都是它下面的地图:(为什么Java不能使这个简单的-_-关联数组都是我想要的）

(Map)array=<string,Object>
(Map)subarray=<String,Object>
(Map)subsubarray=<String,Object>
(Map)subsubcontents=<String,String>

可能不是最有效的阅读方法，计划稍后将其转换为递归函数，但这是我的代码，从我的项目中复制粘贴。 我把评论放在我发现错误的地方。

public static Map<String,Object> array=new HashMap<String,Object>();

/* Code for populating the following Maps and pushing them into array
<String,Object>subarray
<String,Object>subsubarray
<String,String>subsubcontents
*/

Set section=array.entrySet();
Iterator sectionI=section.iterator();
while(sectionI.hasNext()) {
    Map.Entry sectionInfo=(Map.Entry)sectionI.next();
    Map<String,Object> subMap=(Map)sectionInfo.getValue();
    Set subSet=subMap.entrySet();
    Iterator subI=subSet.iterator();
    while(subI.hasNext()) {
            Map.Entry subInfo=(Map.Entry)subI.next();
            Map<String,Object> subsubMap=(Map)subInfo.getValue();
            Set subsubSet=subsubMap.entrySet();
            Iterator subsubI=subsubSet.iterator();
            while(subsubI.hasNext()) {
                    System.out.println("test");
                    Map.Entry subsubInfo=(Map.Entry)subsubI.next();
                    Map<String,Object> subcontentsMap=(Map)subsubInfo.getValue();
/*
The above line seems to be causing the issues.
If you comment out the rest of this loop (below this comment)
the error will still appear. If you comment out the rest of this loop
(including the line above this comment) it disappears.
Power of deduction my dear Watson.
*/
                    Set subcontentsSet=subcontentsMap.entrySet();
                    Iterator keys=subcontentsSet.iterator();
                    while(keys.hasNext()) {
                        Map.Entry keyMap=(Map.Entry)keys.next();
                    }
                    Iterator values=subcontentsSet.iterator();
                    while(values.hasNext()) {
                        Map.Entry valueMap=(Map.Entry)values.next();
                    }
            }
    }
}

任何帮助将非常感激。 我几天都在努力解决这个问题。

Answer 1

我认为你需要清理你的泛型开头：

Set<Map.Entry<String, Object>> section = array.entrySet();
Iterator<Map.Entry<String, Object>> sectionI = section.iterator();
while (sectionI.hasNext()) {
    Map.Entry<String, Object> sectionInfo = sectionI.next();
    Map<String, Object> subMap = (Map<String, Object>) sectionInfo.getValue(); // is this actually a Map<String, Object>?
    Set<Map.Entry<String, Object>> subSet = subMap.entrySet();
    Iterator<Map.Entry<String, Object>> subI = subSet.iterator();
    while (subI.hasNext()) {
        Map.Entry<String, Object> subInfo = subI.next();
        Map<String, Object> subsubMap = (Map<String, Object>) subInfo.getValue(); // is this actually a Map<String, Object>?
        Set<Map.Entry<String, Object>> subsubSet = subsubMap.entrySet();
        Iterator<Map.Entry<String, Object>> subsubI = subsubSet.iterator();
        while (subsubI.hasNext()) {
            System.out.println("test");
            Map.Entry<String, Object> subsubInfo = subsubI.next();
            Map<String, Object> subcontentsMap = (Map<String, Object>) subsubInfo.getValue(); // somehow a String got in here?
/*
The above line seems to be causing the issues.
If you comment out the rest of this loop (below this comment)
the error will still appear. If you comment out the rest of this loop
(including the line above this comment) it disappears.
Power of deduction my dear Watson.
*/
            Set<Map.Entry<String, Object>> subcontentsSet = subcontentsMap.entrySet();
            Iterator<Map.Entry<String, Object>> keys = subcontentsSet.iterator();
            while (keys.hasNext()) {
                Map.Entry<String, Object> keyMap = keys.next();
            }
            Iterator<Map.Entry<String, Object>> values = subcontentsSet.iterator();
            while (values.hasNext()) {
                Map.Entry<String, Object> valueMap = values.next();
            }
        }
    }
}

然后，您应该更明确地声明array ：

public static Map<String, Map<String, Map<String, Map<String, String>>>> array = new HashMap<String, Map<String, Map<String, Map<String, String>>>>();

这将确保您将正确的对象放入每个地图中。 您永远无法put String值放在期望Map<>位置，因为它不会编译。 这将允许您编写以下代码（无需强制转换）：

final Set<Map.Entry<String, Map<String, Map<String, Map<String, String>>>>> section = array.entrySet();
final Iterator<Map.Entry<String, Map<String, Map<String, Map<String, String>>>>> sectionI = section.iterator();
while (sectionI.hasNext()) {
    final Entry<String, Map<String, Map<String, Map<String, String>>>> sectionInfo = sectionI.next();
    final Map<String, Map<String, Map<String, String>>> subMap = sectionInfo.getValue();
    final Set<Map.Entry<String, Map<String, Map<String, String>>>> subSet = subMap.entrySet();
    final Iterator<Map.Entry<String, Map<String, Map<String, String>>>> subI = subSet.iterator();
    while (subI.hasNext()) {
        final Map.Entry<String, Map<String, Map<String, String>>> subInfo = subI.next();
        final Map<String, Map<String, String>> subsubMap = subInfo.getValue();
        final Set<Map.Entry<String, Map<String, String>>> subsubSet = subsubMap.entrySet();
        final Iterator<Map.Entry<String, Map<String, String>>> subsubI = subsubSet.iterator();
        while (subsubI.hasNext()) {
            System.out.println("test");
            final Map.Entry<String, Map<String, String>> subsubInfo = subsubI.next();
            final Map<String, String> subcontentsMap = subsubInfo.getValue();
            final Set<Map.Entry<String, String>> subcontentsSet = subcontentsMap.entrySet();
            final Iterator<Map.Entry<String, String>> entries = subcontentsSet.iterator();
            while (entries.hasNext()) {
                final Map.Entry<String, String> entry = entries.next();
            }
        }
    }
}

总而言之，所有这些嵌套的泛型看起来都很难看。 我建议你创建一些对象来表示你的数据。

Answer 2

你可以这样做 ：

Gson gson = new GsonBuilder().setPrettyPrinting().create();
JsonElement element = gson.fromJson (jsonString, JsonElement.class);
JsonObject jsonObj = element.getAsJsonObject();
Map<String,Object> resultMap = new Gson().fromJson(jsonObj, Map.class);

Answer 3

例外情况告诉你一切。 这个调用subsubInfo.getValue(); 实际上是返回一个String而不是Map ，因此在创建地图时会出现逻辑错误。

如果您将声明更改为Map<String, Map>而不是Map<String, Object>编译器将向您发出警告