Java getter用于类的不存在的属性 [英] Java getter for non-existent attribute of class

问题描述

我在Java中使用了一些我并不理解的功能，因此我想阅读它以便我可以更有效地使用它。问题是我不知道它叫什么，因此很难获得更多信息：

I'm using some functionality in Java that I don't really understand so I want to read up on it so that I can use it more effectively. The problem is that I don't know what it is called so it makes it difficult to get more information on it:

我有一个班级 Foo 定义如下：

I have a class Foo defined like this:

private String _name;
private Bar _bar;
//getters and setters

和 Bar ：

private String _code;

//getters and setters

public String get_isCodeSmith()
{
      boolean rVal =  _code.toLowerCase().contains("smith");        
      return rVal;
}

不知何故，在我的JSP页面中（当我有会话变量名为 Foo ）我能够编写如下逻辑标记：

Somehow, in my JSP pages (when I have a Session variable called Foo) I am able to write logic tags like this:

<logic:equal name="Foo" property="_bar._isCodeSmith" value="true">

即使没有属性 _isCodeSmith 在我的班级 Bar 中，它会自动运行 get_isCodeSmith（）方法。

And even though there is no attribute _isCodeSmith in my class Bar, it runs the get_isCodeSmith() method automatically.

这叫什么，我在哪里可以找到更多？

What is this called and where can I find out more?

推荐答案

这是 Javabeans机制。属性不是由字段标识，而是由getter（访问器）和/或setter（mutator）方法标识。

This is the Javabeans mechanism. Properties are identified not by fields, but by getter (accessor) and / or setter (mutator) methods.

有关更多技术信息，请阅读 JavaBeans规范

For more technical info, read the JavaBeans spec

或者看看这个简单的测试类：

Or have a look at this simple test class:

public class TestBean {

    private String complete;
    public String getComplete() { return complete; }
    public void setComplete(final String complete) { this.complete = complete; }

    private String getterOnly;
    public String getGetterOnly() { return getterOnly; }

    private String setterOnly;
    public void setSetterOnly(final String setterOnly) { this.setterOnly = setterOnly; }

    public String getNoBackingField() { return ""; }

}

和简单的JavaBeans分析：

and the simple JavaBeans analysis:

public class Test {
    public static void analyzeBeanProperties(final Class<?> clazz) throws Exception {
        for (final PropertyDescriptor propertyDescriptor
                : Introspector.getBeanInfo(clazz, Object.class).getPropertyDescriptors()) {
            System.out.println("Property name: " + propertyDescriptor.getName());
            System.out.println("Getter method: " + propertyDescriptor.getReadMethod());
            System.out.println("Setter method: " + propertyDescriptor.getWriteMethod());
            System.out.println();
        }
    }

    public static void main(final String[] args) throws Exception {
        analyzeBeanProperties(TestBean.class);
    }
}

输出

Property name: complete
Getter method: public java.lang.String test.bean.TestBean.getComplete()
Setter method: public void test.bean.TestBean.setComplete(java.lang.String)

Property name: getterOnly
Getter method: public java.lang.String test.bean.TestBean.getGetterOnly()
Setter method: null

Property name: noBackingField
Getter method: public java.lang.String test.bean.TestBean.getNoBackingField()
Setter method: null

Property name: setterOnly
Getter method: null
Setter method: public void test.bean.TestBean.setSetterOnly(java.lang.String)

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