java 解析csv

opencsv

java读取csv的类库主要有两种,opencsv和javacsv,研究发现,javacsv最后一次更新是2014-12-10,很久不维护了。opencsv是apache的项目,并且至今仍在维护,所以决定使用opencsv。


csv

csv文件,全名 comma separated values,默认以逗号分隔,是纯文本文件。虽然用excel打开后格式排版了,但是那是excel对他进行了处理。用notepad或者sublime text打开能看到最原始的文本。
为了后续举例,这里编辑了一个test.csv

header1,header2,header3
1,a,10
2,b,20
3,c,30
4,d,40
5,e,50
6,f,60

读取方式

  • 最原始的方式,逐行读取,然后操作
 CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));

      /*
       * 逐行读取
       */
      String[] strArr = null;
      while((strArr = reader.readNext())!=null){
          System.out.println(strArr[0]+"---"+strArr[1]+"----"+strArr[2]);
      }

      reader.close();

绑定csv文件转换成bean

逐行读取操作是最原始的操作方式,opencsv提供了基于“策略”的映射,将csv绑定到bean。

策略简介

观察一下策略的继承层次
这里写图片描述

接口

  • MappingStrategy
    • 映射的顶层接口
  • HeaderColumnNameMappingStrategy
    • 列名映射策略,读取csv文件第一行作为header,比如header1,header2,header3,然后调用bean的setHeader1方法,setHeader2方法,setHeader3方法分别设置值,所以这种策略要求,列名与bean中的属性名完全一致,如果不一致,则值为空,不会出错。使用注解时,注解名字必须与csv中列名一致。
  • ColumnPositionMappingStrategy
    • 列位置映射策略,他没有header的概念,所以会输出取所有行。在columnMapping数组中指定bean的属性,第一个值对应csv的第一列,第二个值对应csv的第二类……
  • HeaderColumnNameTranslateMappingStrategy
    • 列头名字翻译映射策略,与HeaderColumnNameMappintStrategy相比,bean的属性名可以与csv列头不一样。通过指定map来映射。

具体映射用法

Java POJO类

public class SimpleBeanInfo {

    private String header1;


    private String header2;

    private String header3;

    public String getHeader1() {
        return header1;
    }

    @Override
    public String toString() {
        return "SimpleBeanInfo [header1=" + header1 + ", header2=" + header2
                + ", header3=" + header3 + "]";
    }

    public void setHeader1(String header1) {
        this.header1 = header1;
    }

    public String getHeader2() {
        return header2;
    }

    public void setHeader2(String header2) {
        this.header2 = header2;
    }

    public String getHeader3() {
        return header3;
    }

    public void setHeader3(String header3) {
        this.header3 = header3;
    }

基于列索引的映射

  • 通俗点来说就是列位置映射,csv文件中的列位置对应到bean中的列

  • 非注解方式

CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));
      /*
       *基于列位置,映射成类 
       */
       //csv文件中的第一列对应类的header,第二列对应类的header2,第三列对应类的header3
      String[] columnMapping={"header1","header2","header3"};
      ColumnPositionMappingStrategy mapper = new ColumnPositionMappingStrategy();
      mapper.setColumnMapping(columnMapping);
      mapper.setType(SimpleBeanInfo.class);
      /* */ 
      CsvToBean  csvToBean = new CsvToBean();

      List list = csvToBean.parse(mapper, reader);

      for(SimpleBeanInfo e : list){
          System.out.println(e);
      }

    }
  • 注解方式
public class SimpleBeanInfo {

    @CsvBindByPosition(position=0)
    private String header1;


    @CsvBindByPosition(position=1)
    private String header2;

    @CsvBindByPosition(position=2)
    private String header3;
}
CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));
 ColumnPositionMappingStrategy mapper = new ColumnPositionMappingStrategy();
      mapper.setType(SimpleBeanInfo.class);
      CsvToBean  csvToBean = new CsvToBean();

      List list = csvToBean.parse(mapper, reader);

      for(SimpleBeanInfo e : list){
          System.out.println(e);
      }

基于列名的映射

  • 非注解方式
 CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));

      /* */ 

      HeaderColumnNameMappingStrategy mapper = new
              HeaderColumnNameMappingStrategy();
      mapper.setType(SimpleBeanInfo.class);
      CsvToBean  csvToBean = new CsvToBean();

      List list = csvToBean.parse(mapper, reader);

      for(SimpleBeanInfo e : list){
          System.out.println(e);
      }
  • 注解方式
public class SimpleBeanInfo {

    @CsvBindByName(column="header1")
    private String header1;


    @CsvBindByName(column="header2")
    private String header2;

    @CsvBindByName(column="header3")
    private String header3;
}
CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));

      HeaderColumnNameMappingStrategy mapper = new
              HeaderColumnNameMappingStrategy();
      mapper.setType(SimpleBeanInfo.class);
      CsvToBean  csvToBean = new CsvToBean();

      List list = csvToBean.parse(mapper, reader);

      for(SimpleBeanInfo e : list){
          System.out.println(e);
      }

基于列名转换映射

 CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));
      /*
       * 基于列名转换,映射成类
      */
      HeaderColumnNameTranslateMappingStrategy<SimpleBeanInfo> mapper = 
              new HeaderColumnNameTranslateMappingStrategy<SimpleBeanInfo>();
      mapper.setType(SimpleBeanInfo.class);

      Map<String,String> columnMapping = new HashMap<String,String>();
      columnMapping.put("header1", "header1");//csv中的header1对应bean的header1
      columnMapping.put("header2", "header2");
      columnMapping.put("header3", "header3");
      mapper.setColumnMapping(columnMapping);

      CsvToBean<SimpleBeanInfo>  csvToBean = new CsvToBean<SimpleBeanInfo>();

      List<SimpleBeanInfo> list = csvToBean.parse(mapper, reader);

      for(SimpleBeanInfo e : list){
          System.out.println(e);
      }

过滤器

opencsv提供了过滤器,可以过滤某些行,比如page header、page footer等

  • 所有的过滤器必须实现CsvToBeanFilter 接口
public class MyCsvToBeanFilter implements CsvToBeanFilter {

        public boolean allowLine(String[] line) {
            //过滤第一列值等于1的行
            if("1".equals(line[0])){
                return false;
            }
            return true;
        }

}
 MyCsvToBeanFilter filter = new MyCsvToBeanFilter();
 List list = csvToBean.parse(mapper, reader,filter);

转化器

类中的属性不一定都是字符串,比如数字、日期等,但是我们从csv中获取到的都是字符串,这种情况就应该使用转化器。
这里定义一个SimpleBeanConverter,继承AbstractBeanField


public class SimpleBeanFieldConverter extends AbstractBeanField<SimpleBeanInfo> {

    @Override
    protected Object convert(String value) throws CsvDataTypeMismatchException,
            CsvRequiredFieldEmptyException, CsvConstraintViolationException {
        Field f = getField();
        if("date".equals(f.getName())){
            try {
                return new SimpleDateFormat("yyyy-MM-dd").parse(value);
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
}

test.csv添加一列header4

header1,header2,header3,header4
1,a,10,2016-05-01
2,b,20,2016-05-02
3,c,30,2016-05-03
4,d,40,2016-05-04
5,e,50,2016-05-05
6,f,60,2016-05-06

SimpleBeanInfo添加属性

@CsvCustomBindByPosition(position=3,converter=SimpleBeanFieldConverter.class)
private Date date;

输出结果
由于ColumnPositionMappingStrategy会连header行也解析,所以第一行会打印异常信息。我们看到header4列已经转换为日期。如果不只一个列需要转换怎么办?在相应的属性上添加注解(@CsvCustomBindByPosition或@CsvCustomBindByName),然后在convert(Object value)中扩展即可

java.text.ParseException: Unparseable date: "header4"
    at java.text.DateFormat.parse(DateFormat.java:357)
    at test_maven.SimpleBeanFieldConverter.convert(SimpleBeanFieldConverter.java:24)
    at com.opencsv.bean.AbstractBeanField.setFieldValue(AbstractBeanField.java:70)
    at com.opencsv.bean.CsvToBean.processField(CsvToBean.java:245)
    at com.opencsv.bean.CsvToBean.processLine(CsvToBean.java:220)
    at com.opencsv.bean.CsvToBean.processLine(CsvToBean.java:189)
    at com.opencsv.bean.CsvToBean.parse(CsvToBean.java:166)
    at com.opencsv.bean.CsvToBean.parse(CsvToBean.java:133)
    at test_maven.TestCSV.main(TestCSV.java:46)
SimpleBeanInfo [header1=header1, header2=header2, header3=header3, date=null]
SimpleBeanInfo [header1=2, header2=b, header3=20, date=Mon May 02 00:00:00 CST 2016]
SimpleBeanInfo [header1=3, header2=c, header3=30, date=Tue May 03 00:00:00 CST 2016]
SimpleBeanInfo [header1=4, header2=d, header3=40, date=Wed May 04 00:00:00 CST 2016]
SimpleBeanInfo [header1=5, header2=e, header3=50, date=Thu May 05 00:00:00 CST 2016]
SimpleBeanInfo [header1=6, header2=f, header3=60, date=Fri May 06 00:00:00 CST 2016]

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