如何使用 Java 中的 Jackson 将地图中的逗号分隔字符串转换为对象中的集合

Question

我是运行下一个节目：

import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class Test {

    private static class Shape {
        private String name;
        private Set<String> colors;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public Set<String> getColors() {
            return colors;
        }

        public void setColors(Set<String> colors) {
            this.colors = colors;
        }
    }

    public static void main(String[] args) {
        ObjectMapper objectMapper = new ObjectMapper();
        Map<String, Object> attributes = new HashMap<>();
        attributes.put("name", "table");
        attributes.put("colors", "blue,green,red,black");
        Shape shape = objectMapper.convertValue(attributes, Shape.class);
    }
}

这里是pom.xml中的依赖：

    <dependencies>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.9.3</version>
        </dependency>
    </dependencies>

我遇到下一个错误：

Exception in thread "main" java.lang.IllegalArgumentException: Cannot deserialize instance of `java.util.HashSet` out of VALUE_STRING token
 at [Source: UNKNOWN; line: -1, column: -1] (through reference chain: com.company.test.Test$Shape["colors"])
    at com.fasterxml.jackson.databind.ObjectMapper._convert(ObjectMapper.java:3751)
    at com.fasterxml.jackson.databind.ObjectMapper.convertValue(ObjectMapper.java:3669)
    at com.company.test.Test.main(Test.java:36)

我试过改成：

    attributes.put("colors", "[blue,green,red,black]");
    AND
    attributes.put("colors", "[\"blue\",\"green\",\"red\",\"black\"]");

但是没有用。解决方法可以是下一个：

    ...
    Set<String> colors = new HashSet<>();
    colors.add("blue");
    colors.add("green");
    colors.add("red");
    colors.add("black");
    attributes.put("colors", colors);
    ...

但是，当前实施不允许该解决方案。您是否想象过如何使用不同的方法来实施？

Answer 1

您可以使用 jackson-dataformats-text 库中的 CsvMapper。还有，需要先把String反序列化成Set<String>，建一个Map最后再转成Shape：

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.dataformat.csv.CsvMapper;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class CsvApp {
    public static void main(String[] args) throws JsonProcessingException {
        CsvMapper mapper = new CsvMapper();

        String array = "blue,green,red,black";
        Map<String, Object> attributes = new HashMap<>();
        attributes.put("name", "table");
        attributes.put("colors", mapper.readValue(array, new TypeReference<Set<String>>() {}));
        Shape shape = mapper.convertValue(attributes, Shape.class);

        System.out.println(shape);
    }
}

如何使用 Java 中的 Jackson 将地图中的逗号分隔字符串转换为对象中的集合

How to convert comma separated string in map to Set in object using Jackson in Java

java

performance

data-processing

jackson

jackson-databind