Java 在VelocityTemplate中使用枚举参数调用方法

我正在使用apache velocity为我的应用程序生成配置文件，我遇到了使用enum参数调用方法的问题，如下所示：

我有一个CurrentcyUtil.java

package velocity;

public class CurrencyUtil {

    public enum TestEnum {
        A("Aaaa"), B("Bbbb");

        private String value;

        private TestEnum(String value) {
            this.value = value;
        }

        public String getValue() {
            return this.value;
        }
    }

    public String test(TestEnum testEnum) {
        return testEnum.getValue();
    }
}

package velocity;

import org.apache.velocity.app.Velocity;
import org.apache.velocity.app.VelocityEngine;
import org.apache.velocity.VelocityContext;

import velocity.CurrencyUtil.TestEnum;

import java.io.*;
import java.util.Properties;

public class Example {

    private String templateFile;

    public Example(String templateFile) {
        this.templateFile = templateFile;
    }

    public void run() {

        StringReader reader = null;
        try {
            Velocity.init();

            VelocityContext context = new VelocityContext();
            CurrencyUtil cu = new CurrencyUtil();
            context.put("cu", cu);
            context.put("enumA", TestEnum.A);

            Properties properties = new Properties();
            properties.put("runtime.log.logsystem.class", "org.apache.velocity.runtime.log.NullLogSystem");
            VelocityEngine engine = new VelocityEngine();
            engine.init(properties);

            // HELIO00022587
            String data = readFile(templateFile);
            if (data == null) {
                return;
            }
            reader = new StringReader(data);

            // HELIO00022587
            StringWriter writer = new StringWriter();
            boolean result = engine.evaluate(context, writer, "Test", reader);
            if (result) {
                writeToFile(writer.toString(), templateFile + ".result");
            }
        } catch (Exception e) {
            System.out.println(e);
        }
    }

    public String readFile(String filePath) throws IOException {
        String data = null;
        InputStream in = null;
        try {
            byte[] cbuf = new byte[8192];
            int n;
            int count = 0;
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            in = new FileInputStream(filePath);
            while ((n = in.read(cbuf)) >= 0) {
                if (n > 0) {
                    out.write(cbuf);
                }
                count += n;
            }
            data = new String(out.toByteArray(), 0, count);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            in.close();
        }
        return data;
    }

    public void writeToFile(String data, String filePath) throws IOException {
        File file = new File(filePath);
        if (file.exists()) {
            file.delete();
        }
        file.createNewFile();
        FileWriter writer = new FileWriter(file);
        writer.write(data);
        writer.flush();
        writer.close();
    }
}

我有Example.java

package velocity;

public class CurrencyUtil {

    public enum TestEnum {
        A("Aaaa"), B("Bbbb");

        private String value;

        private TestEnum(String value) {
            this.value = value;
        }

        public String getValue() {
            return this.value;
        }
    }

    public String test(TestEnum testEnum) {
        return testEnum.getValue();
    }
}

package velocity;

import org.apache.velocity.app.Velocity;
import org.apache.velocity.app.VelocityEngine;
import org.apache.velocity.VelocityContext;

import velocity.CurrencyUtil.TestEnum;

import java.io.*;
import java.util.Properties;

public class Example {

    private String templateFile;

    public Example(String templateFile) {
        this.templateFile = templateFile;
    }

    public void run() {

        StringReader reader = null;
        try {
            Velocity.init();

            VelocityContext context = new VelocityContext();
            CurrencyUtil cu = new CurrencyUtil();
            context.put("cu", cu);
            context.put("enumA", TestEnum.A);

            Properties properties = new Properties();
            properties.put("runtime.log.logsystem.class", "org.apache.velocity.runtime.log.NullLogSystem");
            VelocityEngine engine = new VelocityEngine();
            engine.init(properties);

            // HELIO00022587
            String data = readFile(templateFile);
            if (data == null) {
                return;
            }
            reader = new StringReader(data);

            // HELIO00022587
            StringWriter writer = new StringWriter();
            boolean result = engine.evaluate(context, writer, "Test", reader);
            if (result) {
                writeToFile(writer.toString(), templateFile + ".result");
            }
        } catch (Exception e) {
            System.out.println(e);
        }
    }

    public String readFile(String filePath) throws IOException {
        String data = null;
        InputStream in = null;
        try {
            byte[] cbuf = new byte[8192];
            int n;
            int count = 0;
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            in = new FileInputStream(filePath);
            while ((n = in.read(cbuf)) >= 0) {
                if (n > 0) {
                    out.write(cbuf);
                }
                count += n;
            }
            data = new String(out.toByteArray(), 0, count);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            in.close();
        }
        return data;
    }

    public void writeToFile(String data, String filePath) throws IOException {
        File file = new File(filePath);
        if (file.exists()) {
            file.delete();
        }
        file.createNewFile();
        FileWriter writer = new FileWriter(file);
        writer.write(data);
        writer.flush();
        writer.close();
    }
}

我有一个模板示例。vm

enumATest=$enumA
enumAValue=$cu.test($enumA)

#set( $enumB = "B")
enumBTest=$enumB
enumBValue=$cu.test($enumB)

输出为：

enumATest=A 
enumAValue=Aaaa => Because enumA is putted to VelocityContext has TestEnum type, so 'test' method execute ok

#set( $enumB = "B") 
enumBTest=B 
enumBValue=$cu.test($enumB) => Variable enumB declare here, so understand as String => Throw NullPoiterException here

我的问题是：如何在模板文件中声明枚举变量？ 请在这方面帮助我，非常感谢