英文:
jackson deserialize primitive types
问题
我一定做错了... 我试图通过使用ObjecMapper反序列化JSON并分配单个原始类型，但我无法让它工作。
JSON存储在名为“jsonTest.json”的文件中，内容如下：
{
"simpleVariable": 100
}
然后我有一个用于读取JSON的方法，其中包含以下代码：
ObjectMapper objectMapper = new ObjectMapper();
Path path = Paths.get("jsonTest.json");
// 将JSON读入JSON节点
JsonNode rootNode;
try (Reader reader = Files.newBufferedReader(path, StandardCharsets.UTF_8)) {
// 读取JSON文件
rootNode = objectMapper.readTree(reader);
} catch(IOException ie) {
rootNode = null;
ie.printStackTrace();
}
// 现在尝试将节点的值分配给一个int变量：
int intVar = objectMapper.readValue(rootNode, int.class);
问题就在这里。当我尝试编译这段代码时，我会得到以下错误：
类型ObjectMapper中的方法readValue(JsonParser, Class
)对于参数(JsonNode, Class )不适用。
所以显然我已经给readValue提供了一个JsonParser对象，但它不能接受，但我又该如何反序列化原始类型呢？
英文:
I must be doing this wrong... I'm trying to assign a single primitive type by deserialising json with ObjecMapper but I can't get it to work.
The json is in a file called "jsonTest.json" which looks like this:
{
"simpleVariable":100
}
I then have a method for reading json with the following code in it:
ObjectMapper objectMapper = new ObjectMapper();
Path path = Paths.get("jsonTest.json");
// read the json into a json node
JsonNode rootNode;
try (Reader reader = Files.newBufferedReader(path, StandardCharsets.UTF_8)) {
// read the json file
rootNode = objectMapper.readTree(reader);
} catch(IOException ie) {
rootNode = null;
ie.printStackTrace();
}
// now attempt to assign the value of the node to an int:
int intVar = objectMapper.readValue(rootNode, int.class);
And herein lies the problem. When I try to compile this code I get the following error:
> The method readValue(JsonParser, Class<T>) in the type ObjectMapper is not applicable for the arguments (JsonNode, Class<Integer>).
So obviously I've fed readValue with a JsonParser object which it can't accept but how else would I deserialise a primitive?
答案1
得分: 0
尝试：
int intVar = rootNode.get("simpleVariable").asInt();
英文:
Try:
int intVar = rootNode.get("simpleVariable").asInt();
答案2
得分: 0
你可以创建一个名为JsonTest.java的类
public class JsonTest {
int simpleVariable; // 与json文件中的名称相同，带有getter和setter方法
public int getSimpleVariable() {
return simpleVariable;
}
public void setSimpleVariable(int simpleVariable) {
this.simpleVariable = simpleVariable;
}
}
然后让Jackson负责解析这些值
示例：
public static void main(String[] args) throws IOException {
ObjectMapper objectMapper = new ObjectMapper();
Path path = Paths.get("jsonTest.json");
JsonTest jsonTest = objectMapper.readValue(path.toFile(), JsonTest.class);
int intVar = jsonTest.getSimpleVariable();
System.out.println("simpleVariable " + intVar);
}
英文:
you can make class named JsonTest.java
public class JsonTest {
int simpleVariable; // same name as in json file with getters and setters
public int getSimpleVariable() {
return simpleVariable;
}
public void setSimpleVariable(int simpleVariable) {
this.simpleVariable = simpleVariable;
}
}
and let jackson take care of parsing the values
Example:
public static void main(String[] args) throws IOException {
ObjectMapper objectMapper = new ObjectMapper();
Path path = Paths.get("jsonTest.json");
JsonTest jsonTest=objectMapper.readValue(path.toFile(), JsonTest.class);
int intVar = jsonTest.getSimpleVariable();
System.out.println("simpleVariable "+intVar );
}
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