Question

我有一种方法，可以使用JsonGenerator将产品对象写入文件。（productToJSON）

我想使用第二种方法，使用JsonGenerator流将HashSet中的所有产品写入JSON文件。我认为打开和关闭流（文件仅包含最后一个产品）存在问题。因此，我可以使用第二种方法打开和关闭流，但是第一种方法不再适用于一种产品。

请让我知道：

是否可以使用2种方法做我想做的事？
有更好的方法吗？

public void productToJSON(Product product, String fileName) throws Exception {
    JsonFactory jsonFactory = new JsonFactory();
    FileOutputStream file = new FileOutputStream(fileName);
    JsonGenerator jsonGen = jsonFactory.createJsonGenerator(file, JsonEncoding.UTF8);
    jsonGen.setPrettyPrinter(new DefaultPrettyPrinter());

    jsonGen.writeStartObject();
    jsonGen.writeStringField("name", product.getName());
    jsonGen.writeNumberField("weight", product.getWeight());
    jsonGen.writeNumberField("stock", product.getStock());
    jsonGen.writeNumberField("price", product.getPrice());
    jsonGen.writeNumberField("rating", product.getRating());
    jsonGen.writeEndObject();
    jsonGen.close();
}

public void productsToJSON(String fileName) throws Exception {
    for (Product p : this.products) {
        this.productToJSON(p, fileName);
    }
}

Answer 1

一种方法-始终将productsToJSON调用：

private void productToJSON(Product product, JsonGenerator jsonGen) throws Exception {
    jsonGen.writeStartObject();
    jsonGen.writeStringField("name", product.getName());
    jsonGen.writeNumberField("weight", product.getWeight());
    jsonGen.writeNumberField("stock", product.getStock());
    jsonGen.writeNumberField("price", product.getPrice());
    jsonGen.writeNumberField("rating", product.getRating());
    jsonGen.writeEndObject();
}

public void productsToJSON(String fileName) throws Exception {
    JsonFactory jsonFactory = new JsonFactory();
    FileOutputStream file = new FileOutputStream(fileName);
    JsonGenerator jsonGen = jsonFactory.createJsonGenerator(file, JsonEncoding.UTF8);
    jsonGen.setPrettyPrinter(new DefaultPrettyPrinter());
    if (this.products.size > 1) {
        jsonGen.writeStartArray(this.products.size)
    }
    for (Product p: this.products) {
        this.productToJSON(p, jsonGen);
    }
    if (this.products.size > 1) {
        jsonGen.writeEndArray()
    }
    jsonGen.close();
}

方法二-一种私有方法和两种公共方法：

private void productToJSON(Product product, JsonGenerator jsonGen) throws Exception {
    jsonGen.writeStartObject();
    jsonGen.writeStringField("name", product.getName());
    jsonGen.writeNumberField("weight", product.getWeight());
    jsonGen.writeNumberField("stock", product.getStock());
    jsonGen.writeNumberField("price", product.getPrice());
    jsonGen.writeNumberField("rating", product.getRating());
    jsonGen.writeEndObject();
}

public void productsToJSON(String fileName) throws Exception {
    JsonFactory jsonFactory = new JsonFactory();
    FileOutputStream file = new FileOutputStream(fileName);
    JsonGenerator jsonGen = jsonFactory.createJsonGenerator(file, JsonEncoding.UTF8);
    jsonGen.setPrettyPrinter(new DefaultPrettyPrinter());
    jsonGen.writeStartArray(this.products.size)
    for (Product p: this.products) {
        this.productToJSON(p, jsonGen);
    }
    jsonGen.writeEndArray()
    jsonGen.close();
}

public void productToJSON(Product p, String fileName) throws Exception {
    JsonFactory jsonFactory = new JsonFactory();
    FileOutputStream file = new FileOutputStream(fileName);
    JsonGenerator jsonGen = jsonFactory.createJsonGenerator(file, JsonEncoding.UTF8);
    jsonGen.setPrettyPrinter(new DefaultPrettyPrinter());
    this.productToJSON(p, jsonGen);
    jsonGen.close();
}

Answer 2

您可以使用ObjectMapper从Java Object创建一个json。 [以及POJO中的Setter-Getter方法]。使用DefaultPrettyPrinter创建ObjectWriter。

注意：无需在JsonGenerator中设置属性。

jsonGen.writeStringField("name", product.getName());

请参阅下面的示例。

    import java.io.File;
    import java.util.ArrayList;
    import java.util.List;
    import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
    import com.fasterxml.jackson.databind.ObjectMapper;
    import com.fasterxml.jackson.databind.ObjectWriter;

    public class Demo {
        public static void main(String[] args) throws Exception {
            List<Product> list = new ArrayList<Product>();
            list.add(new Product("Sample Product", 123012));
            list.add(new Product("Sample 1 Product 1", 2134));
            list.add(new Product("Sample 1 Product 2", 4353));
            list.add(new Product("Sample 1 Product 3", 34345));
            productsToJSON(list, "Test.txt");
        }

        private static void productsToJSON(List<Product> products, String fileName) throws Exception {
            ObjectMapper mapper = new ObjectMapper();
            ObjectWriter writer = mapper.writer(new DefaultPrettyPrinter());
            writer.writeValue(new File(fileName), products);
        }
    }

    class Product {
        private String name;
        private Integer weight;

        public Product(String name, Integer weight) {
            this.name = name;
            this.weight = weight;
        }

        public String getName() {
            return name;
        }

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

        public Integer getWeight() {
            return weight;
        }

        public void setWeight(Integer weight) {
            this.weight = weight;
        }
    }

输出：

    [ {
      "name" : "Sample Product",
      "weight" : 123012
    }, {
      "name" : "Sample1 Product1",
      "weight" : 123012
    } ]

为集合中的每个元素调用JsonGenerator方法

2 个答案: