我如何序列化&反序列化CSV正确？ [英] How do I serialize & deserialize CSV properly?

问题描述

我一直在尝试将对象序列化为CSV String ，但对象包含 List 和 @JsonUnwrapped 在列表对象上不起作用。

预期示例输出：

：

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

strong>实际输出：

  com.fasterxml.jackson.core.JsonGenerationException：无法识别的列'name'：
  

这里是我的代码 :(大部分是2 POJO的） / p>

  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>部分; 
 
 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）; 
} 
 
} 
  

没有什么我试图似乎工作，我已阅读关于stackoverflow和github的每个帖子，但我可以找到一个有效的解决方案。

对于任何无意义的注释，我遗漏了没有理由，如果你回答代码，请随时删除它们。

解决方案

从错误中，我想相信它与你的模式有关的 > > > > on Car 而不是name





您可能想在其中添加parts，但您会得到与<$ c相同的错误$ c>name不是该模式的一部分。

对代码进行了一些更改后，我能够序列化和反序列化 Car 对象。

部分

这里，经过一些其他修改后，单个String值，因此添加

  @JsonPropertyOrder（{name}）
 public static class Part {
 @JsonProperty（name）
私有字符串名称; 
 
 public Part（）{
 this（）; 
} 
 
 public Part（String partJSON）{
 // TODO：取消序列化参数...它是一个序列化的部分字符串... 
 this.name = partJSON; 
} 
  

车

在这里，您需要实现一个方法，它将 List< Part> 手动转换为CSV可读格式。

这样的方法看起来像这样

  @JsonGetter $ b public String getPartString（）{
 String separator =;; 
 StringBuilder sb = new StringBuilder（）; 
 
迭代器< 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（）; 
} 
  

此外，不要忘记修复类顶部的模式

  @JsonPropertyOrder（{color，parts}）
 public static class Car {
 
 @JsonProperty（color）
 private String color; 
 @JsonProperty（parts）
 private List< Part>部分; 
 
 public Car（）{
 this.parts = new ArrayList<>（）; 
} 
  

序列化

您可以更改 serialize 方法将类的类型作为通用类型参数，而不是显式的 Class 这样。

  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）; 
} 
  

主要作家
$ b

现在，如果你序列化一个 Car ，你应该看到

  color，parts 
 red，gearbox; door; bumper 
  

主要读者

读取CSV字符串并循环遍历 Car.getParts c>

  Car car = mapper.readerFor（Car.class）.with（csvSchema）.readValue（csv）; 
 
 for（Part p：car.getParts（））{
 System.out.println（p.getName（））; 
} 
  







  gearbox 
 door 
 bumper 
  




I've been trying to serialize an object to a CSV String but the object contains a List and @JsonUnwrapped doesn't work on List objects.

Expected sample output:

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

Actual output:

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

Here is my code: (Most of it is the 2 POJO's)

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);
}

}

Nothing I try seems to work, I've read every post on stackoverflow and github about the topic but I can't find a working solution.

Sorry about any pointless annotations that I've left behind for no reason and if you answer with code, please feel free to remove them.

解决方案

From the error, I would like to believe that it has something to do with your schema for a Car, which has the columns of {"color"} taken from @JsonPropertyOrder on Car and not a "name" value.

You probably want to add "parts" in there, but you would get the same error that "name" is not part of that schema.

After a few changes to your code, I was able to serialize and deserialize a Car object.

Part

Here, after some other changes it needed a constructor with a single String value, so add that

@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;
    }

Car

Here, you will need to implement a method that will convert the List<Part> into a CSV-readable format manually.

Such a method would look like this

@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();
} 

Also, don't forget to fix the schema at the top of the class

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

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

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

serialize

You can change your serialize method to take the type of the class as a generic type parameter instead of an explicit Class like so.

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);
}

main - writer

Now, if you serialize a Car, you should see

color,parts
red,gearbox;door;bumper

main - reader

And reading that CSV string and looping over the 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

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