Question

我正在编写一个程序，我需要从json文件中获取一些数据，内容如下所示。

{
    "culture": "en-us",
    "subscription_key": "myKey",
    "description": "myDescription",
    "name": "myName",
    "appID": "myAppId",
    "entities": [
        {
            "name": "Location"
        },
        {
            "name": "geography"
        }
    ]
}

使用在线工具我为此创建了POJO。它们如下所示。

ConfigDetails Pojo

package com.config;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
    "culture",
    "subscription_key",
    "description",
    "name",
    "appID",
    "entities"
})
public class ConfigDetails {

    @JsonProperty("culture")
    private String culture;
    @JsonProperty("subscription_key")
    private String subscriptionKey;
    @JsonProperty("description")
    private String description;
    @JsonProperty("name")
    private String name;
    @JsonProperty("appID")
    private String appID;
    @JsonProperty("entities")
    private List<Entity> entities = null;

    @JsonProperty("culture")
    public String getCulture() {
        return culture;
    }

    @JsonProperty("culture")
    public void setCulture(String culture) {
        this.culture = culture;
    }

    @JsonProperty("subscription_key")
    public String getSubscriptionKey() {
        return subscriptionKey;
    }

    @JsonProperty("subscription_key")
    public void setSubscriptionKey(String subscriptionKey) {
        this.subscriptionKey = subscriptionKey;
    }

    @JsonProperty("description")
    public String getDescription() {
        return description;
    }

    @JsonProperty("description")
    public void setDescription(String description) {
        this.description = description;
    }

    @JsonProperty("name")
    public String getName() {
        return name;
    }

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

    @JsonProperty("appID")
    public String getAppID() {
        return appID;
    }

    @JsonProperty("appID")
    public void setAppID(String appID) {
        this.appID = appID;
    }

    @JsonProperty("entities")
    public List<Entity> getEntities() {
        return entities;
    }

    @JsonProperty("entities")
    public void setEntities(List<Entity> entities) {
        this.entities = entities;
    }
}

实体POJO

package com.config;

import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
    "name"
})
public class Entity {

    @JsonProperty("name")
    private String name;

    @JsonProperty("name")
    public String getName() {
        return name;
    }

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

我正在使用以下代码打印文件中的值。

MainClass obj = new MainClass();
        ObjectMapper mapper = new ObjectMapper();

        try {

            // Convert JSON string from file to Object
            ConfigDetails details = mapper.readValue(new File("properties.json"), ConfigDetails.class);
            System.out.println(details.getAppID());

            List entities = details.getEntities();
            for (Object entity : entities) {
                System.out.println(entity.toString());
            }
        } catch (JsonGenerationException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

我得到的输出是

MyAppId
com.config.Entity@2096442d
com.config.Entity@9f70c54

此处不是打印可用值，而是打印Hashcode。请告诉我如何打印这些值。

由于

Answer 1

只需像这样访问getter方法entity.getName()，然后使用Entity代替Object：

MainClass obj = new MainClass();
    ObjectMapper mapper = new ObjectMapper();

    try {

        // Convert JSON string from file to Object
        ConfigDetails details = mapper.readValue(new File("properties.json"), ConfigDetails.class);
        System.out.println(details.getAppID());

        List entities = details.getEntities();
        for (Entity entity : entities) {
            System.out.println(entity.getName());
        }
    } catch (JsonGenerationException e) {
        e.printStackTrace();
    } catch (JsonMappingException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

Answer 2

您尚未定义将“实体”转换为字符串的含义，因此Java将回归到默认的方式（即打印类名和对象ID）。

当您说要“打印可用值”时，您的意思是什么？在这种情况下，值是Entity类型的Java对象，您基本上是打印值。

您可以通过覆盖toString（）方法来控制对象的String表示形式。例如，您可以将以下内容添加到Entity类：

@Override
public String toString() {
    return "An entity named " + name;
}

使用jackson打印json数组

2 个答案: