无法在Apache velocity中显示对象的实例变量

Question

我试图使用Apache速度显示一些信息，但它似乎不起作用。

Follwing是代码段。

package velocitydemo;

import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;

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

class Vehicle {
    private String vname;
    private Wheel wheel;
    private String type;    
    /**
     * @return the vname
     */
    public String getVname() {
        return vname;
    }

    /**
     * @param vname the vname to set
     */
    public void setVname(String vname) {
        this.vname = vname;
    }

    /**
     * @return the wheel
     */
    public Wheel getWheel() {
        return wheel;
    }

    /**
     * @param wheel the wheel to set
     */
    public void setWheel(Wheel wheel) {
        this.wheel = wheel;
    }

    /**
     * @return the type
     */
    public String getType() {
        return type;
    }

    /**
     * @param type the type to set
     */
    public void setType(String type) {
        this.type = type;
    }

    /**
     * @return the model
     */
    public int getModel() {
        return model;
    }

    /**
     * @param model the model to set
     */
    public void setModel(int model) {
        this.model = model;
    }

    private int model;

    public Vehicle(String name, Wheel wheel, String type, int model) {
        super();
        this.vname = name;
        this.wheel = wheel;
        this.type = type;
        this.model = model;
    }
}

class Wheel {
    private String type;
    private String name;

    /**
     * @return the type
     */
    public String getType() {
        return type;
    }

    /**
     * @param type the type to set
     */
    public void setType(String type) {
        this.type = type;
    }

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    public Wheel(String type, String name) {
        super();
        this.type = type;
        this.name = name;
    }
}

public class HelloWorld {
    private static List<String> list = new ArrayList<String>();

    public static void main(String[] args) throws Exception {

        Vehicle vh = constructVehicle("Model S", "Vinyl", "JK", "Electric", 2014);

        VelocityEngine ve = new VelocityEngine();
        ve.init();
        /* next, get the Template */
        Template t = ve.getTemplate("helloworld.vm");
        /* create a context and add data */
        VelocityContext context = new VelocityContext();
        context.put("name", "World");
        context.put("name2", "foobar");
        context.put("name3", "flash");
        context.put("vehicle", vh);
        StringWriter writer = new StringWriter();
        t.merge(context, writer);
        System.out.println(writer.toString());
    }

    public static Vehicle constructVehicle(String vehicleName, String wheelType, String wheelName, String vhType, int model) {
        Wheel wl = new Wheel(wheelType, wheelName);
        Vehicle vh = new Vehicle(vehicleName, wl, vhType, model);

        return vh;
    }
}

速度模板是helloworld.vm，其中包含以下信息

Hello $name!  Welcome to Velocity!
Hello $name2!  Welcome to Velocity!
Hello $name3!  Welcome to Velocity!
Car is  $vehicle.vname
Car is  $vehicle.getVname()
Car is  $vehicle.hashCode()  and model is $vehicle.getModel()

然而输出是：

Hello World!  Welcome to Velocity!
Hello foobar!  Welcome to Velocity!
Hello flash!  Welcome to Velocity!


Car is  $vehicle.vname
Car is  $vehicle.getVname()
Car is  14872264  and model is $vehicle.getModel()

我不明白为什么类车辆的变量没有得到解决。