tl;dr
使用 CSV 实用程序,例如Apache 共享 CSV,每一行传入数据都可以传递给您编写的解析方法,并得到结果Employee
对象收集到List
.
Iterable < CSVRecord > iterable = CSVFormat.RFC4180.withFirstRecordAsHeader().parse( reader );
employees =
StreamSupport
.stream( iterable.spliterator() , false )
.map( ( CSVRecord csvRecord ) -> Employee.parse( csvRecord ) )
.collect( Collectors.toList() )
;
That Employee.parse
方法将数据从CSVRecord
做一个Employee
object.
UUID id = UUID.fromString( csvRecord.get( "id" ) ) ;
String name = csvRecord.get( "name" ) ;
return new Employee( id , name ) ;
Details
是的,您可以加载List
来自 CSV 文件。
首先,获取 CSV 解析实用程序,例如 https://commons.apache.org/proper/commons-csv/。 Java 生态系统中有多种此类工具可供选择。
然后定义一个Employee
具有解析 CSV 输入的工厂方法的类。对于 Apache Commons CSV,这将是CSVRecord
object.
重要的parse
的方法Employee
class.
// Parsing from Apache Commons CSV record
static public Employee parse ( CSVRecord csvRecord )
{
UUID id = UUID.fromString( Objects.requireNonNull( csvRecord.get( "id" ) ) );
String name = Objects.requireNonNull( csvRecord.get( "name" ) );
Employee employee = new Employee( id , name );
Objects.requireNonNull( employee );
return employee;
}
整个Employee
类源代码。
package work.basil.example;
import org.apache.commons.csv.CSVRecord;
import java.util.Objects;
import java.util.UUID;
public class Employee
{
// Member fields.
private UUID id;
private String name;
// Constructor.
public Employee ( UUID id , String name )
{
this.id = Objects.requireNonNull( id );
this.name = Objects.requireNonNull( name );
if ( this.name.isBlank() ) { throw new IllegalArgumentException(); }
}
// Parsing from Apache Commons CSV record
static public Employee parse ( CSVRecord csvRecord )
{
UUID id = UUID.fromString( Objects.requireNonNull( csvRecord.get( "id" ) ) );
String name = Objects.requireNonNull( csvRecord.get( "name" ) );
Employee employee = new Employee( id , name );
Objects.requireNonNull( employee );
return employee;
}
// Object overrides.
@Override
public String toString ( )
{
return "Employee{ " +
"id=" + id +
" | name='" + name + '\'' +
" }";
}
@Override
public boolean equals ( Object o )
{
if ( this == o ) return true;
if ( o == null || getClass() != o.getClass() ) return false;
Employee employee = ( Employee ) o;
return getId().equals( employee.getId() );
}
@Override
public int hashCode ( )
{
return Objects.hash( getId() );
}
// Getters.
public UUID getId ( ) { return this.id; }
public String getName ( ) { return this.name; }
}
这是使用该工厂方法来生成的演示List
of Employee
CSV 文件中的记录。这main
这里的方法首先创建一个文件。请注意,第一行是标题行,声明每列的名称。我们在解析代码中使用该名称。
id,name
ac4f0541-4f39-4b8a-a49b-5e88405da503,Alice
ca4a3950-e7a1-4521-993f-1d4c78ecda8c,Bob
67ef39f8-688f-4795-8b41-76d972cad888,Carol
然后我们读取新创建的文件,使用 Apache Commons CSV 将每一行解析为CSVRecord
我们将其传递给静态方法Employee.parse
。我们得到一个Employee
record.
在我们的例子中Apache 共享 CSV,我们得到一个Iterable
of CSVRecord
对象。我们将其转换为Iterable to a Stream using StreamSupport正如问题中所讨论的,使用 Java 8 JDK 将 Iterable 转换为 Stream.
演示代码的核心。
List < Employee > employees = List.of(); // Default to empty non-modifiable list.
Path path = Paths.get( "/Users/basilbourque/csv.txt" );
try (
Reader reader = Files.newBufferedReader( path , StandardCharsets.UTF_8 ) ;
)
{
Iterable < CSVRecord > iterable = CSVFormat.RFC4180.withFirstRecordAsHeader().parse( reader );
employees =
StreamSupport
.stream( iterable.spliterator() , false )
.map( ( CSVRecord csvRecord ) -> Employee.parse( csvRecord ) )
.collect( Collectors.toList() )
;
}
catch ( IOException e )
{
e.printStackTrace();
}
完整的演示代码。
package work.basil.example;
import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVPrinter;
import org.apache.commons.csv.CSVRecord;
import java.io.*;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.time.Duration;
import java.time.Instant;
import java.util.List;
import java.util.UUID;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;
public class EmployeeDemo
{
public static void main ( String[] args )
{
EmployeeDemo app = new EmployeeDemo();
app.write();
app.read();
}
private void write ( )
{
Path path = Paths.get( "/Users/basilbourque/csv.txt" );
try (
Writer writer = Files.newBufferedWriter( path , StandardCharsets.UTF_8 ) ;
CSVPrinter printer = new CSVPrinter( writer , CSVFormat.RFC4180 ) ;
)
{
printer.printRecord( "id" , "name" );
printer.printRecord( UUID.randomUUID() , "Alice" );
printer.printRecord( UUID.randomUUID() , "Bob" );
printer.printRecord( UUID.randomUUID() , "Carol" );
}
catch ( IOException ex )
{
ex.printStackTrace();
}
}
private void read ( )
{
List < Employee > employees = List.of(); // Default to empty non-modifiable list.
Path path = Paths.get( "/Users/basilbourque/csv.txt" );
try (
Reader reader = Files.newBufferedReader( path , StandardCharsets.UTF_8 ) ;
)
{
Iterable < CSVRecord > iterable = CSVFormat.RFC4180.withFirstRecordAsHeader().parse( reader );
employees =
StreamSupport
.stream( iterable.spliterator() , false )
.map( ( CSVRecord csvRecord ) -> Employee.parse( csvRecord ) )
.collect( Collectors.toList() )
;
}
catch ( IOException e )
{
e.printStackTrace();
}
System.out.println( "employees = " + employees );
}
}
运行时。
员工= [员工{ id=ac4f0541-4f39-4b8a-a49b-5e88405da503 | name='Alice' }, 员工{ id=ca4a3950-e7a1-4521-993f-1d4c78ecda8c | name='Bob' }, 员工{ id=67ef39f8-688f-4795-8b41-76d972cad888 |名称='卡罗尔'}]