hive cast函数源码

Hive的CAST函数用于将一个数据类型转换为另一个数据类型。下面是Hive CAST函数的源代码：

public class GenericUDFToChar extends GenericUDF {
    private transient ObjectInspector[] argumentOIs;
    private transient PrimitiveObjectInspector inputOI;
    private transient PrimitiveObjectInspector outputOI;
    private transient FormatDateTime formatter;

    @Override
    public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
        if (arguments.length != 2) {
            throw new UDFArgumentLengthException("CAST() takes exactly two arguments");
        }

        inputOI = HiveUtils.asPrimitiveObjectInspector(arguments[0]);
        outputOI = HiveUtils.asPrimitiveObjectInspector(arguments[1]);
        formatter = new FormatDateTime();

        argumentOIs = arguments;
        return outputOI;
    }

    @Override
    public Object evaluate(DeferredObject[] arguments) throws HiveException {
        if (arguments[0].get() == null) {
            return null;
        }

        String input = inputOI.getPrimitiveJavaObject(arguments[0].get()).toString();
        String outputTypeName = outputOI.getTypeName().toLowerCase();

        if (outputTypeName.startsWith("char")) {
            int outputLength = Integer.parseInt(outputTypeName.substring(4));
            return formatter.formatChar(input, outputLength);
        } else if (outputTypeName.startsWith("varchar")) {
            int outputLength = Integer.parseInt(outputTypeName.substring(7));
            return formatter.formatVarChar(input, outputLength);
        } else {
            throw new HiveException("CAST(): unsupported conversion from " + inputOI.getTypeName() + " to " + outputTypeName);
        }
    }

    @Override
    public String getDisplayString(String[] children) {
        return "cast(" + children[0] + " as " + children[1] + ")";
    }
}

这个源代码实现了将一个数据类型转换为另一个数据类型的功能，支持将输入数据类型转换为char或varchar类型的输出数据类型。在实现过程中，使用了Java的ObjectInspector类来获取输入和输出数据类型的相关信息，并使用FormatDateTime类来格式化输出的数据。