如何在java中按对象值对JsonNode进行排序

Question

如何根据产品节点的成本变量按升序或降序获得排序值？或者如何通过在下面的 JsonNode 响应中排序来修改产品节点的值？

JsonNode 响应：

{
    "products": [
        {
            "Name": "Marble",
            "cost": 47.49
        },
        {
            "Name": "Mixer",
            "cost": 59.99
        },
        {
            "Name": "Soap",
            "cost": 3.99
        }
    ],
    "details": [
        {
            "area": 1090.098
        }
    ]
}

降序的异常响应：

{
    "products": [
        {
            "Name": "Mixer",
            "cost": 59.99
        },
        {
            "Name": "Marble",
            "cost": 47.49
        },
        {
            "Name": "Soap",
            "cost": 3.99
        }
    ],
    "details": [
        {
            "area": 1090.098
        }
    ]
}

请用正确的解决方案指导我，我厌倦了使用比较器但是JsonNode响应中的这个产品节点没有任何POJO类，所以我不能使用obj.StringName进行比较。

Answer 1

以下解决方案使用包javax.json.* 来解析和生成JSON。

import java.util.*;
import java.io.*;
import javax.json.*;

public class Products
{
    // This is an "internal" method that loads the JSON to a String
    static final String json = LFEC.loadFile("products.json");
    
    public static void main(String[] argv) throws IOException
    {
        // *********** Parse Input Json *****************
        // Save the products in a sorted TreeMap...
        // NOTE: We will have to "resort it" afterwards..
        // **********************************************
        TreeMap<String, Double> productsSortedByName = new TreeMap<>();

        // Retrieve the JsonObject's
        JsonObject   obj         = Json.createReader(new StringReader(json)).readObject();
        JsonArray    products    = obj.getJsonArray("products");
        
        for (JsonObject product : products.getValuesAs(JsonObject.class))
        {
            // Retreives the product name and price for each product
            String name = product.getString("Name");
            double cost = product.getJsonNumber("cost").doubleValue();

            // Save in a Java TreeMap<String, Double> 
            // NOTE:  TreeMap sorts by the "Key" (not the value)

            productsSortedByName.put(name, Double.valueOf(cost));
        }
        
        // ******** Sort Products by Price **************
        // Since the question requires that the TreeMap sort by price, not product name...
        // This shall build a new TreeMap that is sorted by the Price
        // This is tricky, because it requires having **TWO** TreeMap's
        // **********************************************

        Comparator<String> comp = (String key1, String key2) -> 
            productsSortedByName.get(key1).compareTo(productsSortedByName.get(key2));

        // Build the TreeMap, and put the contents of the original TreeMap into the new one
        TreeMap<String, Double> productsSortedByPrice = new TreeMap<>(comp);
        productsSortedByPrice.putAll(productsSortedByName);
        
        // ********* Products are Sorted ****************
        // Now build the sorted JSON - this part is "self-explanatory."
        // AGAIN, this is how the JDK package "javax.json.*" can be used to create JSON
        // ********* Build Output Json ******************

        JsonArrayBuilder arrBuilder = Json.createArrayBuilder();
        
        for (String product : productsSortedByPrice.keySet())
            arrBuilder.add(Json.createObjectBuilder()
                .add("name", product)
                .add("cost", productsSortedByPrice.get(product).doubleValue()));
        
        String sortedJson = Json
            .createObjectBuilder()
            .add("products", arrBuilder)
            .add("details", obj.getJsonArray("details"))
            .build()
            .toString();
        
        // Print out the sorted JSON to terminal...
        System.out.println(sortedJson);
    }
}

以上代码将在终端输出以下内容：

{"products":[{"name":"Soap","cost":3.99},{"name":"Marble","cost":47.49},{"name":"Mixer","cost":59.99}],"details":[{"area":1090.098}]}

Answer 2

如果您不想为数据模型创建 POJO，可以使用 javax.json.json-api 库直接使用 JSON。

查看我的 maven 文件（在代码示例之后），了解我添加到项目中的依赖项列表。

package so;
import java.io.StringReader;
import java.io.StringWriter;

import javax.json.*;


public class SortExample {
    
    public JsonObject sortProductsByPrice(JsonObject order) {
        
        JsonArray products = order.getJsonArray("products");
        JsonArray details = order.getJsonArray("details");
        
        JsonArrayBuilder arrayBuilder = Json.createArrayBuilder();

        
        products.stream().sorted((product1, product2) -> {
            JsonNumber cost1 = product1.asJsonObject().getJsonNumber("cost");
            JsonNumber cost2 = product2.asJsonObject().getJsonNumber("cost");
            return Double.compare(cost1.doubleValue(), cost2.doubleValue());
        }).forEach((value) -> arrayBuilder.add(value));
        
        
        JsonObjectBuilder objectBuilder = Json.createObjectBuilder();
        
        objectBuilder.add("products", arrayBuilder.build());
        objectBuilder.add("details", details);
        
        return objectBuilder.build();
        
    }

    public static void main(String[] args) {
        
        String orderString = 
                "{\"products\": [ {\"Name\": \"Marble\",\"cost\": 47.49 }, { \"Name\": \"Mixer\",  \"cost\": 59.99  },  { \"Name\": \"Soap\", \"cost\": 3.99  } ], \"details\" : [ { \"area\" : 1090.098  } ] }";
        
                
        JsonObject order = Json.createReader(new StringReader(orderString)).readObject();
        
        JsonObject sortedOrder = new SortExample().sortProductsByPrice(order);
        
        StringWriter writer = new StringWriter();
        Json.createWriter(writer).writeObject(sortedOrder);
        
        System.out.println(writer.toString());
    }

}

打印：

{"products":[{"Name":"Soap","cost":3.99},{"Name":"Marble","cost":47.49},{"Name":"Mixer","cost":59.99}],"details":[{"area":1090.098}]}

我的示例中的main 方法只是从您的示例中构造有效负载。工作在sortProductsByPrice完成。

它只是将产品保留在其JsonValue 表示中，并使用流式 API 对其进行排序，然后将它们放回新的JsonArray，最后使用原始details 和排序的产品构建一个新的JsonObject .

我不熟悉 javax.json 并且找不到漂亮的打印选项。也许有更好的库可用。但这为您提供了您想要做什么的要点。

依赖关系：

        <dependency>
            <groupId>javax.json</groupId>
            <artifactId>javax.json-api</artifactId>
            <version>1.1.4</version>
        </dependency>
        <dependency>
            <groupId>org.glassfish</groupId>
            <artifactId>javax.json</artifactId>
            <version>1.1.4</version>
        </dependency>