问题
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.
回答1:
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
回答2:
Full working CSV Serialize & Deserialize solution:
import com.fasterxml.jackson.annotation.JsonGetter;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.databind.MappingIterator;
import com.fasterxml.jackson.dataformat.csv.CsvMapper;
import com.fasterxml.jackson.dataformat.csv.CsvSchema;
import java.io.IOException;
import java.util.ArrayList;
import static java.util.Arrays.asList;
import java.util.Iterator;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
public class NestedWrapping {
@JsonPropertyOrder({"color", "parts"})
public static class Car {
@JsonProperty("color")
private String color;
@JsonProperty("parts")
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;
}
public Car() {
this.parts = new ArrayList<>();
}
@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();
}
@Override
public String toString() {
return "Car{" + "color=" + color + ", parts=" + parts + '}';
}
}
@JsonPropertyOrder({
"name"
})
public static class Part {
@JsonProperty("name")
private String name;
public Part() {
}
public Part(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Part{" + "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));
String serialized = serialize(car, Car.class, true);
System.out.println("serialized: " + serialized);
List<Car> deserializedCars = (List) deserialize(serialized, Car.class, true);
for (Car deserializedCar : deserializedCars) {
System.out.println("deserialized: " + deserializedCar.toString());
}
} 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);
}
public static final synchronized List<Object> deserialize(final String csv, final Class type, final Boolean hasHeaders) throws IOException {
CsvMapper csvMapper = new CsvMapper();
CsvSchema csvSchema;
if (hasHeaders) {
csvSchema = csvMapper.schemaFor(type).withHeader();
} else {
csvSchema = csvMapper.schemaFor(type).withoutHeader();
}
MappingIterator<Object> mappingIterator = csvMapper.readerFor(type).with(csvSchema).readValues(csv);
List<Object> objects = new ArrayList<>();
while (mappingIterator.hasNext()) {
objects.add(mappingIterator.next());
}
return objects;
}
}
来源：https://stackoverflow.com/questions/36943511/how-do-i-serialize-deserialize-csv-properly