java-如何正确序列化和反序列化CSV？

我一直在尝试将对象序列化为CSV字符串,但是该对象包含一个List,并且@JsonUnwrapped在List对象上不起作用.

预期样本输出：

color,part.name\n
red,gearbox\n
red,door\n
red,bumper

实际输出：

com.fasterxml.jackson.core.JsonGenerationException: Unrecognized column 'name':

这是我的代码：(其中大多数是2个POJO)

import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.annotation.JsonRootName;
import com.fasterxml.jackson.dataformat.csv.CsvMapper;
import com.fasterxml.jackson.dataformat.csv.CsvSchema;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import java.io.IOException;
import static java.util.Arrays.asList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

public class NestedWrapping {

@JsonRootName("Car")
@JsonInclude(JsonInclude.Include.NON_DEFAULT)
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY, getterVisibility = JsonAutoDetect.Visibility.NONE, setterVisibility = JsonAutoDetect.Visibility.NONE)
@JsonPropertyOrder({"color"})
public static class Car {

    @JsonProperty("color")
    private String color;

    @JsonFormat(shape = JsonFormat.Shape.STRING)
    @JacksonXmlElementWrapper(useWrapping = false)
    private List<Part> parts;

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public List<Part> getParts() {
        return parts;
    }

    public void setParts(List<Part> parts) {
        this.parts = parts;
    }

}

@JsonInclude(JsonInclude.Include.NON_DEFAULT)
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY, getterVisibility = JsonAutoDetect.Visibility.NONE, setterVisibility = JsonAutoDetect.Visibility.NONE)
@JsonPropertyOrder({
    "name"
})
public static class Part {

    @JsonProperty("name")
    private String name;

    public String getName() {
        return name;
    }

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

}

public static void main(String args[]) {
    try {
        Car car = new Car();
        car.setColor("red");
        Part part1 = new Part();
        part1.setName("geabox");
        Part part2 = new Part();
        part2.setName("door");
        Part part3 = new Part();
        part3.setName("bumper");
        car.setParts(asList(part1, part2, part3));
        System.out.println("serialized: " + serialize(car, Car.class, true));
    } catch (IOException ex) {
        Logger.getLogger(NestedWrapping.class.getName()).log(Level.SEVERE, null, ex);
    }
}

public static final synchronized String serialize(final Object object, final Class type, final Boolean withHeaders) throws IOException {
    CsvMapper csvMapper = new CsvMapper();
    CsvSchema csvSchema;
    if (withHeaders) {
        csvSchema = csvMapper.schemaFor(type).withHeader();
    } else {
        csvSchema = csvMapper.schemaFor(type).withoutHeader();
    }
    return csvMapper.writer(csvSchema).writeValueAsString(object);
}

}

我尝试执行的所有操作似乎都没有效果,但我已经在stackoverflow和github上阅读了有关该主题的所有post,但找不到有效的解决方案.

抱歉,我无缘无故留下的毫无意义的注释,如果您使用代码回答,请随时将其删除.

解决方法:

从错误中,我想相信这与您的Car模式有关,该模式具有{“ color”}列,这些列取自Car上的@JsonPropertyOrder,而不是“ name”值.

您可能想在其中添加“部分”,但是会收到相同的错误,即“名称”不属于该架构.

在对您的代码进行了一些更改之后,我得以对Car对象进行序列化和反序列化.

部分

在这里,经过一些其他更改,它需要一个具有单个String值的构造函数,因此添加

@JsonPropertyOrder({"name"})
public static class Part {
    @JsonProperty("name")
    private String name;

    public Part() {
        this("");
    }

    public Part(String partJSON) {
        // TODO: Unserialize the parameter... it is a serialized Part string... 
        this.name = partJSON;
    }

汽车

在这里,您将需要实现一种方法,该方法将转换List< Part>手动转换为CSV可读格式.

这样的方法看起来像这样

@JsonGetter("parts")
public String getPartString() {
    String separator = ";";
    StringBuilder sb = new StringBuilder();

    Iterator<Part> iter = this.parts.iterator();
    while (iter.hasNext()) {
        Part p = iter.next();
        sb.append(p.getName());

        if (iter.hasNext())
            sb.append(separator);
    }

    return sb.toString();
} 

另外,不要忘记将模式固定在类的顶部

@JsonPropertyOrder({"color", "parts"})
public static class Car {

    @JsonProperty("color")
    private String color;
    @JsonProperty("parts")
    private List<Part> parts;

    public Car() {
        this.parts = new ArrayList<>();
    }

连载

您可以更改序列化方法,以将类的类型作为通用类型参数,而不是像这样的显式类.

public static final synchronized <T> String serialize(final T object, final Boolean withHeaders) throws IOException {
    CsvMapper csvMapper = new CsvMapper();
    CsvSchema csvSchema = csvMapper.schemaFor(object.getClass());

    if (withHeaders) {
        csvSchema = csvSchema.withHeader();
    } else {
        csvSchema = csvSchema.withoutHeader();
    }

    return csvMapper.writer(csvSchema).writeValueAsString(object);
}

主-作家

现在,如果您序列化了Car,您应该会看到

color,parts
red,gearbox;door;bumper

主要-读者

并读取该CSV字符串并遍历Car.getParts()

Car car = mapper.readerFor(Car.class).with(csvSchema).readValue(csv);

for (Part p : car.getParts()) {
    System.out.println(p.getName());
}

gearbox
door
bumper

标签：unmarshalling,java,csv,marshalling,jackson-dataformat-csv
来源： https://codeday.me/bug/20191014/1912432.html