Question

基本上我正在使用

编写JSON文件

private void setupDictionaries() {
    ObjectMapper mapper = new ObjectMapper();
    ArrayNode arrayNode = mapper.createArrayNode();
    JsonNode rootNode = mapper.createObjectNode();
    ArrayList<String> myThing = new ArrayList<String>();
    myThing.add("hi");
    myThing.add(".");

    itemsDict.put("cake", myThing);

    JsonNode childNode1 = mapper.valueToTree(itemsDict);
    ((ObjectNode) rootNode).set("Jan",  childNode1);
    JsonNode childNode2 = mapper.createObjectNode();
    ((ObjectNode) rootNode).set("obj2", childNode2);
    JsonNode childNode3 = mapper.createObjectNode();
    ((ObjectNode) rootNode).set("obj3", childNode3);
    String jsonString;
    try {
        jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(rootNode);
        System.out.println(jsonString);
        ObjectWriter writer = mapper.writer(new DefaultPrettyPrinter());
        writer.writeValue(new File(statsFile), jsonString);
    } catch (JsonProcessingException e2) {
        // TODO Auto-generated catch block
        e2.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

在这个JSON文件中，我想要为所有12个月生成一个类似的字典，并且只加载我想要专门使用的字典。但是，由于这些不是简单的HashMaps，当我尝试加载json文件时，我得到了异常。装货代码：

private HashMap<String, List<String>> loadDict() {
    ObjectMapper mapper = new ObjectMapper();
    try {
        HashMap<String, ArrayList<String>> map = mapper.readValue(new File(statsFile), new TypeReference<HashMap<String, ArrayList<String>>>() {});
        //Object map = mapper.readValue(new File(statsFile), new TypeReference<Object>() {});
        System.out.println(map.get("cake");
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

例外：

com.fasterxml.jackson.databind.JsonMappingException：无法构造java.util.HashMap的实例：no String-argument构造函数/工厂方法从String值反序列化

我的JSON文件：

{ “Jan”：{ “蛋糕”：[“hi”，“。” ] }， “obj2”：{}， “obj3”：{} }

编辑：我想我找出了导致它的原因

String input = new String(Files.readAllBytes(Paths.get(statsFile)));
        System.out.println(input);
        String input1 = "{\r\n  \"Jan\" : {\r\n    \"cake\" : [ \"hi\", \".\" ]\r\n  },\r\n  \"obj2\" : { },\r\n  \"obj3\" : { }\r\n}";
        System.out.println(input1);

运行此代码，输入为：

“{\ r \ n \”Jan \“：{\ r \ n \”蛋糕\“：[\”hi \“，\”。\“] \ r \ n}，\ r \ n＆n＆gt; ; \“obj2 \”：{}，\ r \ n \“obj3 \”：{} \ r \ n}“ { “Jan”：{ “蛋糕”：[“hi”，“。” ] }， “obj2”：{}， “obj3”：{} } （基本上从一个文件中读取，所有这些都在一行上，其中在输入字符串中具有实际的json字符串，它很好且干净，分成多行）现在我只需要弄清楚如何克服这个......

解决我不得不将jsonString写入文件，而是编写rootNode

private void setupDictionaries() {
    ObjectMapper mapper = new ObjectMapper();
    ObjectWriter writer = mapper.writer(new DefaultPrettyPrinter());

    ArrayNode arrayNode = mapper.createArrayNode();
    JsonNode rootNode = mapper.createObjectNode();
    ArrayList<String> myThing = new ArrayList<String>();
    myThing.add("hi");
    myThing.add(".");

    itemsDict.put("cake", myThing);

    JsonNode childNode1 = mapper.valueToTree(itemsDict);
    ((ObjectNode) rootNode).set("Jan",  childNode1);
    JsonNode childNode2 = mapper.createObjectNode();
    ((ObjectNode) rootNode).set("obj2", childNode2);
    JsonNode childNode3 = mapper.createObjectNode();
    ((ObjectNode) rootNode).set("obj3", childNode3);
    String jsonString;
    try {
        //jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(rootNode);
        System.out.println(rootNode);
        writer.writeValue(new File(statsFile), rootNode);
    } catch (JsonProcessingException e2) {
        // TODO Auto-generated catch block
        e2.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

我可以简单地通过

查询

private HashMap<String, List<String>> loadDict() {
    ObjectMapper mapper = new ObjectMapper();
    try {
        System.out.println("...");
        HashMap<String, HashMap<String, ArrayList<String>>> map = mapper.readValue(new File(statsFile), new TypeReference<HashMap<String, HashMap<String, ArrayList<String>>>>() {});
        System.out.println(map.get("Jan").get("cake").get(0));
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

谢谢大家

Answer 1

问题在于您的TypeReference。您的示例JSON类似于HashMap<String, HashMap<String, ArrayList<String>>>

对于HashMap<String, ArrayList<String>>，JSON应该类似于

{＆＃34; Jan＆＃34; ：[＆＃34; hi＆＃34;，＆＃34;。＆＃34; ]，＆＃34; obj2＆＃34; ：[]，＆＃34; obj3＆＃34; ：[]}

<强>更新

测试您的示例JSON：

public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
    String input = "{ \"Jan\" : { \"cake\" : [ \"hi\", \".\" ] }, \"obj2\" : { }, \"obj3\" : { } }";
    ObjectMapper mapper = new ObjectMapper();
    HashMap<String, HashMap<String, ArrayList<String>>> map = mapper.readValue(input,
            new TypeReference<HashMap<String, HashMap<String, ArrayList<String>>>>() {
            });
    System.out.println(map.get("Jan").get("cake").get(0));

}

如何使用Jackson从JSON文件加载多个HashMaps

1 个答案: