java.lang.ClassCastException : java. lang.String 无法转换为 java.lang.Boolean，使用 Table.addRow() 和 Jackcess

Question

我正在尝试使用 Jackcess 在 MS Access 数据库中写入一些值。我的值最初是使用 String 表示的。我使用的代码如下:

int nColumns = 0;

// get table from internal representation
ModelDatabaseTable table = this.DB.getTable(tableName);

// create new table
TableBuilder DBTableBuilder = new TableBuilder(tableName);

// get table's columns and their Jackcess datatype    
Map<String, DataType> columns = table.getColumns();

// for each column, insert it in the actual database
for (String columnName : columns.keySet()) {
    DataType dt = columns.get(columnName);
    ColumnBuilder cb = new ColumnBuilder(columnName).setType(dt);
    if (dt.isVariableLength()) {
        cb.setMaxLength();
    }
    DBTableBuilder.addColumn(cb);
    nColumns += 1;
}

// if columns were inserted
if (nColumns > 0) {
    // write table to actual database
    Table DBTable = DBTableBuilder.toTable(this.DBConnection);

    // for each row
    for (ModelDatabaseRow row : table.getRows()) {

        // get list of values (represented using String)
        List<String> values = new ArrayList<String>();

        // for each column get its value and insert it in values
        for (String columnName : columns.keySet()) {
            String columnValue = row.getColumn(columnName);
            values.add(columnValue);
        }

        // print current row
        System.out.println(values.toString());

        // insert row in database table. Exception rises here:
        // java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Boolean
        DBTable.addRow(values.toArray());
    }
}

下面是一个不起作用的基本示例(常规数据使用 JSON 描述)。在这种情况下，例程在尝试插入 BOOLEAN 值(HasM、HasZ)时停止，但它能够插入 DOUBLE 值 - 这些值都作为参数提供给 Table.addRow() 函数作为一个字符串数组。

{
  "tables": {
    "Table1": {
      "rows": [
      {
        "items": {
        "ExtentBottom": "45.050715999999994",
        "ExtentLeft": "7.644834000000003",
        "ExtentRight": "7.670400999999998",
        "ExtentTop": "45.07392899999999",
        "FieldName": "Shape",
        "HasM": "false",
        "HasZ": "false",
        "IdxGridSize": "3.7252903001966386E-7",
        "IdxOriginX": "0.0",
        "IdxOriginY": "0.0",
        "MHigh": "NaN",
        "MLow": "NaN",
        "SRID": "1",
        "ShapeType": "4",
        "TableName": "GDB_Items",
        "ZHigh": "NaN",
        "ZLow": "NaN"
        }
      },
      {
        "items": {
        "ExtentBottom": "4989476.8181",
        "ExtentLeft": "393329.1171000004",
        "ExtentRight": "395300.25320000015",
        "ExtentTop": "4992023.569399999",
        "FieldName": "Shape",
        "HasM": "false",
        "HasZ": "false",
        "IdxGridSize": "0.009311329524584121",
        "IdxOriginX": "0.0",
        "IdxOriginY": "0.0",
        "MHigh": "NaN",
        "MLow": "NaN",
        "SRID": "2",
        "ShapeType": "4",
        "TableName": "Building_DIMMER_01",
        "ZHigh": "NaN",
        "ZLow": "NaN"
        }
      }
      ],
      "columns": {
      "ExtentBottom": "DOUBLE",
      "ExtentLeft": "DOUBLE",
      "ExtentRight": "DOUBLE",
      "ExtentTop": "DOUBLE",
      "FieldName": "TEXT",
      "HasM": "BOOLEAN",
      "HasZ": "BOOLEAN",
      "IdxGridSize": "DOUBLE",
      "IdxOriginX": "DOUBLE",
      "IdxOriginY": "DOUBLE",
      "MHigh": "DOUBLE",
      "MLow": "DOUBLE",
      "SRID": "LONG",
      "ShapeType": "LONG",
      "TableName": "TEXT",
      "ZHigh": "DOUBLE",
      "ZLow": "DOUBLE"
      } 
    }
  }
}

前面的 JSON 表示我的程序使用的数据的内部表示，它的结构是这样的:

{
  "tables": {
    "TableName": {
      "rows": [
        {
          "items: {
            "columnName1": "columnValue1",
            ...
            "columnNameN": "columnValueN"
           }
        },
        {
          "items: {
            "columnName1": "columnValue1",
            ...
            "columnNameN": "columnValueN"
           }
        }
      ],
      "columns": {
        "columnName1": "columnDataType1",
        ...
        "columnNameN": "columnDataTypeN"
      }
    }
  }
}

不懂的可以问我，

谢谢

Answer 1

Jackcess 通常希望使用强类型的 Java 对象。在这种情况下，Jackcess 必须尝试通过在添加行时自动将 String 转换为 Double 来提供帮助。无论出于何种原因，Jackcess 不愿意自动将 String 转换为 Boolean^{*/sup>，即使这种转换看起来很明显(对我们来说)，所以对于带有字段的表}

ID:自动编号，主键
DoubleField:数字( double )
YesnoField:是/否

下面的代码会抛出你看到的异常

String doubleFieldValue = "3.14159";
String yesnoFieldValue = "true";
tbl.addRow(Column.AUTO_NUMBER, doubleFieldValue, yesnoFieldValue);

但是，这会起作用

String doubleFieldValue = "3.14159";
String yesnoFieldValue = "true";
tbl.addRow(Column.AUTO_NUMBER, doubleFieldValue, Boolean.parseBoolean(yesnoFieldValue));

作为一般规则，最好在使用 Jackcess 时尝试使用正确类型的对象以避免像这样的小“意外”，所以按权利我们确实应该使用

String doubleFieldValue = "3.14159";
String yesnoFieldValue = "true";
tbl.addRow(Column.AUTO_NUMBER, Double.parseDouble(doubleFieldValue), Boolean.parseBoolean(yesnoFieldValue));

^* 编辑:2015-03-21

今天发布的 Jackcess 2.0.9 添加了将 String 值自动转换为 Boolean 的功能。