目前无法Map
使用CsvSchema
. 进程使用com.fasterxml.jackson.databind.deser.std.MapDeserializer
现在不检查模式。我们可以编写自定义Map
反序列化器。GitHub上有一个问题:CsvMapper does not respect CsvSchema.ColumnType when using @JsonAnySetter wherecowtowncoder
回答:
在这一点上,模式类型并没有太多用于任何事情,但我同意它应该这样做。
编辑
com.fasterxml.jackson.databind.deser.std.MapDeserializer
我决定仔细看看我们可以用幕后使用的事实做些什么。实现Map
将处理类型的自定义反序列化器将很难实现和注册,但我们可以使用有关ValueInstantiator
. 让我们定义Map
一个知道如何处理ColumnType
信息的新类型:
class CsvMap extends HashMap<String, Object> {
private final CsvSchema schema;
private final NumberFormat numberFormat = NumberFormat.getInstance();
public CsvMap(CsvSchema schema) {
this.schema = schema;
}
@Override
public Object put(String key, Object value) {
value = convertIfNeeded(key, value);
return super.put(key, value);
}
private Object convertIfNeeded(String key, Object value) {
CsvSchema.Column column = schema.column(key);
if (column.getType() == CsvSchema.ColumnType.NUMBER) {
try {
return numberFormat.parse(value.toString());
} catch (ParseException e) {
// leave it as it is
}
}
return value;
}
}
对于没有构造函数的新类型,no-arg
我们应该创建新的ValueInstantiator
:
class CsvMapInstantiator extends ValueInstantiator.Base {
private final CsvSchema schema;
public CsvMapInstantiator(CsvSchema schema) {
super(CsvMap.class);
this.schema = schema;
}
@Override
public Object createUsingDefault(DeserializationContext ctxt) {
return new CsvMap(schema);
}
@Override
public boolean canCreateUsingDefault() {
return true;
}
}
示例用法:
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.MappingIterator;
import com.fasterxml.jackson.databind.ObjectReader;
import com.fasterxml.jackson.databind.deser.ValueInstantiator;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.dataformat.csv.CsvMapper;
import com.fasterxml.jackson.dataformat.csv.CsvSchema;
import java.io.File;
import java.io.IOException;
import java.text.NumberFormat;
import java.text.ParseException;
import java.util.HashMap;
public class CsvApp {
public static void main(String[] args) throws IOException {
File csvFile = new File("./resource/test.csv").getAbsoluteFile();
CsvSchema schema = CsvSchema.builder()
.addColumn("firstName", CsvSchema.ColumnType.STRING)
.addColumn("lastName", CsvSchema.ColumnType.STRING)
.addColumn("age", CsvSchema.ColumnType.NUMBER)
.build().withHeader();
// Create schema aware map module
SimpleModule csvMapModule = new SimpleModule();
csvMapModule.addValueInstantiator(CsvMap.class, new CsvMapInstantiator(schema));
// register map
CsvMapper csvMapper = new CsvMapper();
csvMapper.registerModule(csvMapModule);
// get reader for CsvMap + schema
ObjectReader objectReaderWithSchema = csvMapper
.readerWithSchemaFor(CsvMap.class)
.with(schema);
MappingIterator<CsvMap> mappingIterator = objectReaderWithSchema.readValues(csvFile);
while (mappingIterator.hasNext()) {
CsvMap entryMap = mappingIterator.next();
Number age = (Number) entryMap.get("age");
System.out.println(age + " (" + age.getClass() + ")");
}
}
}
以下CSV
有效载荷的代码:
firstName,lastName,age
John,Doe,21
Error,Name,-10.1
印刷:
21 (class java.lang.Long)
-10.1 (class java.lang.Double)
它看起来像一个黑客,但我想展示这种可能性。