java - groovy.lang.Binding属性和变量的区别

Question

无法真正弄清楚/找到两者之间的区别

import groovy.lang.Binding;
import groovy.lang.GroovyShell;

class Scratch {
    public static void main(String[] args) {
        Binding binding = new Binding();
        Integer p = 1,
                v = 1;
        binding.setProperty("p", p);
        binding.setVariable("v", v);

        GroovyShell shell = new GroovyShell(binding);
        shell.evaluate("p++;v++;");
        System.out.println(String.format("BINDING Property = %s, Variable = %s", binding.getProperty("p"), binding.getVariable("v")));
        System.out.println(String.format("JAVA Property = %s, Variable = %s", p, v));
    }
}

输出是:

BINDING Property = 2, Variable = 2
JAVA Property = 1, Variable = 1

使用一个或另一个是否有某种目的。

Answer 1

groovy.lang.Binding 类重载了 setProperty 和 getProperty 方法，因此您可以使用字段访问器或下标运算符访问变量。如果您查看这两种方法的源代码，您会发现类似这样的内容:

/**
 * Overloaded to make variables appear as bean properties or via the subscript operator
 */
public Object getProperty(String property) {
    /** @todo we should check if we have the property with the metaClass instead of try/catch  */
    try {
        return super.getProperty(property);
    }
    catch (MissingPropertyException e) {
        return getVariable(property);
    }
}

/**
 * Overloaded to make variables appear as bean properties or via the subscript operator
 */
public void setProperty(String property, Object newValue) {
    /** @todo we should check if we have the property with the metaClass instead of try/catch  */
    try {
        super.setProperty(property, newValue);
    }
    catch (MissingPropertyException e) {
        setVariable(property, newValue);
    }
}

这意味着在 Groovy 中你可以表达

binding.setVariable("v", v);

作为

binding.v = v
// or
binding['v'] = v

当然，如果您使用 setProperty 或 getProperty 访问的属性存在于类中，那么您将无法使用此名称和在在这种情况下，您需要直接调用 binding.setVariable()。

另一方面，方法 getVariable 和 setVariable 直接读取或将值放入内部映射。这是它的源代码:

/**
 * @param name the name of the variable to lookup
 * @return the variable value
 */
public Object getVariable(String name) {
    if (variables == null)
        throw new MissingPropertyException(name, this.getClass());

    Object result = variables.get(name);

    if (result == null && !variables.containsKey(name)) {
        throw new MissingPropertyException(name, this.getClass());
    }

    return result;
}

/**
 * Sets the value of the given variable
 *
 * @param name  the name of the variable to set
 * @param value the new value for the given variable
 */
public void setVariable(String name, Object value) {
    if (variables == null)
        variables = new LinkedHashMap();
    variables.put(name, value);
}