使用SuperCSV ICsvBeanReader解析枚举

Question

我解析CSV文件并使用supercsv创建域对象。我的域对象有一个枚举字段，例如：

public class TypeWithEnum {

private Type type;

public TypeWithEnum(Type type) {
    this.type = type;
}

public Type getType() {
    return type;
}

public void setType(Type type) {
    this.type = type;
}
}

我的枚举看起来像这样：

public enum Type {

    CANCEL, REFUND
}

正在尝试从此CSV文件创建bean：

final String[] header = new String[]{ "type"  };
ICsvBeanReader inFile = new CsvBeanReader(new FileReader(
    getFilePath(this.getClass(), "learning/enums.csv")), CsvPreference.STANDARD_PREFERENCE);

final CellProcessor[] processors = 
    new CellProcessor[]{ TODO WHAT TO PUT HERE? };
TypeWithEnum myEnum = inFile.read(
    TypeWithEnum.class, header, processors);

填充对象上下文时此操作失败并出现错误: null违规处理器:在org.supercsv.io.CsvBeanReader.read(未知源)的org.supercsv.io.CsvBeanReader.fillObject(Unknown源处为null

关于解析枚举有什么建议吗？我应该为此编写自己的处理器吗？

我已经尝试编写自己的处理器了，就像这样：

class MyCellProcessor extends CellProcessorAdaptor {
    public Object execute(Object value, CSVContext context) {
        Type type = Type.valueOf(value.toString());
        return next.execute(type, context);
    }
}

但它会以同样的异常消亡。

我的enums.csv文件的内容很简单：

取消

退款

Answer 1

您得到的异常是因为CsvBeanReader不能实例化您的TypeWithEnum类，因为它没有默认(无参数)构造函数。打印堆栈跟踪可能是一个好主意，这样您就可以看到错误的全部细节。

Super CSV依赖于这样一个事实，即您应该提供一个有效的Java bean，即一个具有默认构造函数和每个字段的公共getter/setter的类。

因此，您可以通过将以下代码添加到TypeWithEnum来修复该异常

public TypeWithEnum(){
}

至于解析枚举的提示，有两个最简单的选项：

1.使用HashMapper处理器

@Test
public void hashMapperTest() throws Exception {

    // two lines of input
    String input = "CANCEL\nREFUND";

    // you could also put the header in the CSV file
    // and use inFile.getCSVHeader(true)
    final String[] header = new String[] { "type" };

    // map from enum name to enum
    final Map<Object, Object> typeMap = new HashMap<Object, Object>();
    for( Type t : Type.values() ) {
        typeMap.put(t.name(), t);
    }

    // HashMapper will convert from the enum name to the enum
    final CellProcessor[] processors = 
        new CellProcessor[] { new HashMapper(typeMap) };

    ICsvBeanReader inFile = 
        new CsvBeanReader(new StringReader(input),
        CsvPreference.STANDARD_PREFERENCE);

    TypeWithEnum myEnum;
    while((myEnum = inFile.read(TypeWithEnum.class, header, processors)) !=null){
        System.out.println(myEnum.getType());
    }

}

2.创建自定义CellProcessor

创建您的处理器

package org.supercsv;

import org.supercsv.cellprocessor.CellProcessorAdaptor;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.exception.SuperCSVException;
import org.supercsv.util.CSVContext;

public class TypeProcessor extends CellProcessorAdaptor {

    public TypeProcessor() {
        super();
    }

    public TypeProcessor(CellProcessor next) {
        super(next);
    }

    public Object execute(Object value, CSVContext context) {

        if (!(value instanceof String)){
            throw new SuperCSVException("input should be a String!");
        }

        // parse the String to a Type
        Type type = Type.valueOf((String) value);

        // execute the next processor in the chain
        return next.execute(type, context);
    }

}

使用它！

@Test
public void customProcessorTest() throws Exception {

    // two lines of input
    String input = "CANCEL\nREFUND";

    final String[] header = new String[] { "type" };

    // HashMapper will convert from the enum name to the enum
    final CellProcessor[] processors = 
        new CellProcessor[] { new TypeProcessor() };

    ICsvBeanReader inFile = 
        new CsvBeanReader(new StringReader(input),
        CsvPreference.STANDARD_PREFERENCE);
    TypeWithEnum myEnum;
    while((myEnum = inFile.read(TypeWithEnum.class, header, processors)) !=null){
        System.out.println(myEnum.getType());
    }

}

我正在开发即将发布的Super CSV。我一定会更新网站，让你清楚地知道你必须有一个有效的Java bean --对于那些不喜欢读Javadoc的人来说，也许还需要一个可用的处理器的描述。

Answer 2

下面是一个用于枚举的通用单元处理器

/** A cell processor to convert strings to enums. */
public class EnumCellProcessor<T extends Enum<T>> implements CellProcessor {

    private Class<T> enumClass;
    private boolean ignoreCase;

    /**
     * @param enumClass the enum class used for conversion
     */
    public EnumCellProcessor(Class<T> enumClass) {
        this.enumClass = enumClass;
    }

    /**
     * @param enumClass the enum class used for conversion
     * @param ignoreCase if true, the conversion is made case insensitive
     */
    public EnumCellProcessor(Class<T> enumClass, boolean ignoreCase) {
        this.enumClass = enumClass;
        this.ignoreCase = ignoreCase;
    }

    @Override
    public Object execute(Object value, CsvContext context) {
        if (value == null)
            return null;

        String valueAsStr = value.toString();

        for (T s : enumClass.getEnumConstants()) {
            if (ignoreCase ? s.name().equalsIgnoreCase(valueAsStr) : s.name().equals(valueAsStr)) {
                return s;
            }
        }

        throw new SuperCsvCellProcessorException(valueAsStr + " cannot be converted to enum " + enumClass.getName(), context, this);
    }

}

你会用到它

new EnumCellProcessor<Type>(Type.class);

Answer 3

我试着重现你的错误，但对我来说一切正常。我使用SuperCSV 1.52：

  private enum ENUMS_VALUES{TEST1, TEST2, TEST3};
  @Test
  public void testEnum3() throws IOException
  {
    String testInput = new String("TEST1\nTEST2\nTEST3");
    ICsvBeanReader  reader = new CsvBeanReader(new StringReader(testInput), CsvPreference.EXCEL_NORTH_EUROPE_PREFERENCE);
    final String[] header = new String[] {"header"};
    reader.read(this.getClass(), header, new CellProcessor[] {new CellProcessorAdaptor() {

      @Override
      public Object execute(Object pValue, CSVContext pContext)
      {
        return next.execute(ENUMS_VALUES.valueOf((String)pValue), pContext);
      }}});

  }

  @Test
  public void testEnum4() throws IOException
  {
    String testInput = new String("TEST1\nTEST2\nTEST3");
    ICsvBeanReader reader = new CsvBeanReader(new StringReader(testInput), CsvPreference.EXCEL_NORTH_EUROPE_PREFERENCE);
    final String[] header = new String[] {"header"};
    reader.read(this.getClass(), header, new CellProcessor[] {new CellProcessorAdaptor()
    {

      @Override
      public Object execute(Object pValue, CSVContext pContext)
      {
        return ENUMS_VALUES.valueOf((String)pValue);
      }}});
  }

  public void setHeader(ENUMS_VALUES value)
  {
    System.out.println(value);
  }