java 解析csv

opencsv

java讀取csv的類庫主要有兩種，opencsv和javacsv，研究發現，javacsv最後一次更新是2014-12-10，很久不維護了。opencsv是apache的項目，並且至今仍在維護，所以決定使用opencsv。 csv

csv檔案，全名 comma separated values，預設以逗號分隔，是純文字檔案。雖然用excel開啟後格式排版了，但是那是excel對他進行了處理。用notepad或者sublime text開啟能看到最原始的文本。
為了後續舉例，這裡編輯了一個test.csv

header1,header2,header31,a,102,b,203,c,304,d,405,e,506,f,60

讀取方式 最原始的方式，逐行讀取，然後操作

 CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));      /*       * 逐行讀取       */      String[] strArr = null;      while((strArr = reader.readNext())!=null){          System.out.println(strArr[0]+"---"+strArr[1]+"----"+strArr[2]);      }      reader.close();

綁定csv檔案轉換成bean

逐行讀取操作是最原始的操作方式，opencsv提供了基於“策略”的映射，將csv綁定到bean。 策略簡介

觀察一下策略的繼承層次
介面 MappingStrategy
映射的頂層介面 HeaderColumnNameMappingStrategy
列名映射策略，讀取csv檔案第一行作為header，比如header1,header2,header3,然後調用bean的setHeader1方法，setHeader2方法，setHeader3方法分別設定值，所以這種策略要求，列名與bean中的屬性名稱完全一致，如果不一致，則值為空白，不會出錯。使用註解時，註解名字必須與csv中列名一致。 ColumnPositionMappingStrategy
列位置映射策略，他沒有header的概念，所以會輸出取所有行。在columnMapping數組中指定bean的屬性，第一個值對應csv的第一列，第二個值對應csv的第二類…… HeaderColumnNameTranslateMappingStrategy
列頭名字翻譯映射策略,與HeaderColumnNameMappintStrategy相比，bean的屬性名稱可以與csv列頭不一樣。通過指定map來映射。 具體映射用法 Java POJO類

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;    }

基於列索引的映射

通俗點來說就是列位置映射，csv檔案中的列位置對應到bean中的列

非註解方式

CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));      /*       *基於列位置，映射成類        */       //csv檔案中的第一列對應類的header，第二列對應類的header2，第三列對應類的header3      String[] columnMapping={"header1","header2","header3"};      ColumnPositionMappingStrategy<SimpleBeanInfo> mapper = new ColumnPositionMappingStrategy<SimpleBeanInfo>();      mapper.setColumnMapping(columnMapping);      mapper.setType(SimpleBeanInfo.class);      /* */       CsvToBean<SimpleBeanInfo>  csvToBean = new CsvToBean<SimpleBeanInfo>();      List<SimpleBeanInfo> list = csvToBean.parse(mapper, reader);      for(SimpleBeanInfo e : list){          System.out.println(e);      }    }

註解方式

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<SimpleBeanInfo> mapper = new ColumnPositionMappingStrategy<SimpleBeanInfo>();      mapper.setType(SimpleBeanInfo.class);      CsvToBean<SimpleBeanInfo>  csvToBean = new CsvToBean<SimpleBeanInfo>();      List<SimpleBeanInfo> list = csvToBean.parse(mapper, reader);      for(SimpleBeanInfo e : list){          System.out.println(e);      }

基於列名的映射 非註解方式

 CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));      /* */       HeaderColumnNameMappingStrategy<SimpleBeanInfo> mapper = new              HeaderColumnNameMappingStrategy<SimpleBeanInfo>();      mapper.setType(SimpleBeanInfo.class);      CsvToBean<SimpleBeanInfo>  csvToBean = new CsvToBean<SimpleBeanInfo>();      List<SimpleBeanInfo> list = csvToBean.parse(mapper, reader);      for(SimpleBeanInfo e : list){          System.out.println(e);      }

註解方式

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<SimpleBeanInfo> mapper = new              HeaderColumnNameMappingStrategy<SimpleBeanInfo>();      mapper.setType(SimpleBeanInfo.class);      CsvToBean<SimpleBeanInfo>  csvToBean = new CsvToBean<SimpleBeanInfo>();      List<SimpleBeanInfo> list = csvToBean.parse(mapper, reader);      for(SimpleBeanInfo e : list){          System.out.println(e);      }

基於列名轉換映射

 CSVReader reader = new CSVReader(new InputStreamReader(new FileInputStream("test.csv"),"gbk"));      /*       * 基於列名轉換，映射成類      */      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對應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);      }

過濾器

opencsv提供了過濾器，可以過濾某些行，比如page header、page footer等 所有的過濾器必須實現CsvToBeanFilter 介面

public class MyCsvToBeanFilter implements CsvToBeanFilter {        public boolean allowLine(String[] line) {            //過濾第一列值等於1的行            if("1".equals(line[0])){                return false;            }            return true;        }}

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

轉化器

類中的屬性不一定都是字串，比如數字、日期等，但是我們從csv中擷取到的都是字串，這種情況就應該使用轉化器。
這裡定義一個SimpleBeanConverter，繼承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,header41,a,10,2016-05-012,b,20,2016-05-023,c,30,2016-05-034,d,40,2016-05-045,e,50,2016-05-056,f,60,2016-05-06

SimpleBeanInfo添加屬性

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

輸出結果
由於ColumnPositionMappingStrategy會連header行也解析，所以第一行會列印異常資訊。我們看到header4列已經轉換為日期。如果不只一個列需要轉換怎麼辦。在相應的屬性上添加註解(@CsvCustomBindByPosition或@CsvCustomBindByName)，然後在convert(Object value)中擴充即可

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]