无法使用Spring MVC / jackson序列化JSON以正确设置

Question

public class Parent {

    private List<Child> childs;

}

public class Parent {

    private Set<Child> childs;

}

@RequestMapping(value = "/save", method = RequestMethod.POST)
public void saveFooter(@RequestBody Parent parent, Model model)

below is the sample JSON object.

{child: [{ name: 'a'}, { name: 'b'}]}

When I use Set for childs in Parent.class, parent.getChilds.size() , the size of childs is 1 only(which is wrong).

But when I use List for childs in Parent.class, parent.getChilds.size() , the size of childs is 2 (which is correct)

Edit:

public class Child {

    private String name;

}

jackson maven dependency

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.4</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.4</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.4</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-hibernate4</artifactId>
            <version>2.4</version>
        </dependency>

Edit：

public class Child {
    private Long id;
    private String name;

    @Override
    public boolean equals(final Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        final Child other = (Child) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        return true;
    } 
}

found out that the problem is due to I implemented the equals method of Child.class which make the two object equal.

Answer 1

Parent.java

package com.test;

import java.util.Set;

public class Parent {

    private Set<Child> childs;

    public Set<Child> getChilds() {
        return childs;
    }

    public void setChilds(Set<Child> childs) {
        this.childs = childs;
    }
}

Child.Java

package com.test;

public class Child {
    private String name;

    public Child(String name) {
        this.name = name;
    }

    public Child() {
    }

    public String getName() {
        return name;
    }

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

Test.java

    package com.test;

import java.io.IOException;
import java.util.HashSet;

import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

import flexjson.JSONSerializer;

public class MvelCompilation {

    public static void main(String[] args) {

        Parent parent = new Parent();
        Child c1 = new Child("Ankur1");
        Child c2 = new Child("Ankur2");

        HashSet<Child> childSet = new HashSet<Child>();
        childSet.add(c1);
        childSet.add(c2);
        parent.setChilds(childSet);

        JSONSerializer serializer = new JSONSerializer();
        System.out.println("Json String is = " + serializer.exclude("*.class").deepSerialize(parent));

        String s = "{\"childs\":[{\"name\":\"Ankur1\"},{\"name\":\"Ankur2\"}]}";

        try {
            Parent parent1 = new ObjectMapper().readValue(s, Parent.class);
            System.out.println("size = " + parent1.getChilds().size());
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

Output

Json String is = {"childs":[{"name":"Ankur1"},{"name":"Ankur2"}]}

size = 2