Java jackson dataformat csv:不带POJO的映射数值
我正在尝试使用Java jackson dataformat csv:不带POJO的映射数值,java,csv,jackson,jackson-dataformat-csv,Java,Csv,Jackson,Jackson Dataformat Csv,我正在尝试使用jackson dataformat CSV解析一个CSV文件,我想将数字列映射到数字java类型 CsvSchema schema = CsvSchema.builder().setUseHeader(true) .addColumn("firstName", CsvSchema.ColumnType.STRING) .addColumn("lastName", CsvSchema.ColumnType.STRING) .addColumn("age",
jackson dataformat CSV
解析一个CSV文件,我想将数字列映射到数字java类型
CsvSchema schema = CsvSchema.builder().setUseHeader(true)
.addColumn("firstName", CsvSchema.ColumnType.STRING)
.addColumn("lastName", CsvSchema.ColumnType.STRING)
.addColumn("age", CsvSchema.ColumnType.NUMBER)
.build();
CsvMapper csvMapper = new CsvMapper();
MappingIterator<Map<String, Object>> mappingIterator = csvMapper
.readerFor(Map.class)
.with(schema)
.readValues(is);
while (mappingIterator.hasNext()) {
Map<String, Object> entryMap = mappingIterator.next();
Number age = (Number) entryMap.get("age");
}
我知道CsvSchema
在POJO中工作得很好,但我需要处理任意的CSV模式,所以我不能为每种情况创建一个新的java类
将CSV解析为键入的
映射
或数组
的任何方法?目前无法使用CsvSchema
配置映射
反序列化。进程使用com.fasterxml.jackson.databind.deser.std.MapDeserializer
,它现在不检查模式。我们可以编写自定义Map
反序列化程序。GitHub上有一个问题:cowtowncoder
回答:
在这一点上,模式类型并没有用于任何事情,但我同意
应该这样
编辑
我决定仔细看看我们能做些什么,因为com.fasterxml.jackson.databind.desr.std.MapDeserializer
在幕后使用。实现定制的Map
反序列化器(它将关注类型)将很难实现和注册,但我们可以使用ValueInstantiator
的相关知识。让我们定义新的Map
type,它知道如何处理ColumnType
info:
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;
}
}
用法示例:
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() + ")");
}
}
}
印刷品:
21 (class java.lang.Long)
-10.1 (class java.lang.Double)
这看起来像一个黑客,但我想展示这种可能性。你可以用它来做这类事情。它更快、更灵活:
CsvParserSettingssettings = new CsvParserSettings(); //configure the parser if needed
CsvParser parser = new CsvParser(settings);
for (Record record : parser.iterateRecords(is)) {
Short age = record.getShort("age");
}
要获取类型化映射,请告诉解析器您正在处理的列的类型:
parser.getRecordMetadata().setTypeOfColumns(Short.class, "age" /*, and other column names*/);
//to get 0 instead of nulls when the field is empty in the file:
parser.getRecordMetadata().setDefaultValueOfColumns("0", "age", /*, and other column names*/);
// then parse
for (Record record : parser.iterateRecords(is)) {
Map<String,Object> map = record.toFieldMap();
}
parser.getRecordMetadata().setTypeOfColumns(Short.class,“age”/*和其他列名*/);
//要在文件中字段为空时获取0而不是null,请执行以下操作:
parser.getRecordMetadata().setDefaultValueOfColumns(“0”、“年龄”、/*和其他列名*/);
//然后解析
for(记录:parser.iteratereRecords(is)){
Map Map=record.toFieldMap();
}
希望这有帮助
免责声明:我是这个图书馆的作者。它是开源和免费的(Apache 2.0许可证)谢谢你,Michał。我将寻找其他解决方案。@IgorLuzhanov,请看第页。@IgorLuzhanov,我知道你已经接受了其他答案,但也许你会发现一些有用的东西。
21 (class java.lang.Long)
-10.1 (class java.lang.Double)
CsvParserSettingssettings = new CsvParserSettings(); //configure the parser if needed
CsvParser parser = new CsvParser(settings);
for (Record record : parser.iterateRecords(is)) {
Short age = record.getShort("age");
}
parser.getRecordMetadata().setTypeOfColumns(Short.class, "age" /*, and other column names*/);
//to get 0 instead of nulls when the field is empty in the file:
parser.getRecordMetadata().setDefaultValueOfColumns("0", "age", /*, and other column names*/);
// then parse
for (Record record : parser.iterateRecords(is)) {
Map<String,Object> map = record.toFieldMap();
}