java使用Jackson将JSON标量读取为singleelement double[]

Question

假设我有以下两个JSON文件

{
  "a": [1, 2]
}

及

{
  "a": 1
}

我想使用Jackson将它们反序列化为以下形式的对象-

public class Foo {
    public double[] a;
}

因此，我将得到两个对象，Foo{a=[1,2]}和Foo{a=[1]}。有没有可能说服Jackson将标量1反序列化为双数组[1]，最好使用Jackson数据绑定api

Answer 1

是的，你可以

通过使用ObjectMapper#.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);习语

这里有一个独立的例子：

package test;

import java.util.Arrays;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Main {

    public static void main( String[] args ) throws Exception {
        ObjectMapper om = new ObjectMapper();
        // configuring as specified         
        om.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
        // scalar example
        String json = "{\"foo\":2}";
        // array example
        String otherJson = "{\"foo\":[3,4,5]}";
        // de-serializing scalar and printing value
        Main m = om.readValue(json, Main.class);
        System.out.println(Arrays.toString(m.foo));
        // de-serializing array and printing value
        Main otherM = om.readValue(otherJson, Main.class);
        System.out.println(Arrays.toString(otherM.foo));
    }
    @JsonProperty(value="foo")
    protected double[] foo;
}

输出

[2.0]
[3.0, 4.0, 5.0]

快速注释

关于杰克逊的版本。ACCEPT_SINGLE_VALUE_AS_ARRAY的文件说：

Note that features that do not indicate version of inclusion were available in Jackson 2.0 (or earlier); only later additions indicate version of inclusion.

该功能没有@sincejavadoc注释，因此它应该在Jackson的最新版本中工作