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从零开始造Spring02---实现setter注入

沪钢木子 2022-06-14 阅读 69

前言

本节我们将要学习如何实现setter 注入。此博文是学习刘欣老师《从零开始造Spring》的学习笔记。

为啥要实现setter 注入

在上一篇博客中我们实现了Bean实例的生成,但是 Bean与Bean之间的依赖关系我们还没有实现,例如:当A类(Bean) 依赖于B类(Bean)时,我们就需要将B类的实例注入到A类中。常见的注入方式有三种:
- setter 注入
- 构造器注入
- 接口注入
接口注入不常用,此处我们主要实现setter注入和构造器注入。首先,我们这篇博客主要讲的就是如何实现setter注入。

数据结构的表达

xml中的配置

<bean id="petStoreService"
class="com.jay.spring.service.v2.PetStoreService">
<property name="accountDao" ref="accountDao"/>
<property name="itemDao" ref="itemDao"/>
<property name="owner" value="xiangwei"/>
<property name="version" value="2"/>
</bean>

<bean id="accountDao" class="com.jay.spring.dao.v2.AccountDao"></bean>
<bean id="itemDao" class="com.jay.spring.dao.v2.ItemDao"/>

思考:我们使用BeanDefinition表达了​​<bean>​​​标签中的id,class。 那么对于property 怎么表达?ref 怎么表达? value 怎么表达?
我们新建一个PropertyValue类用于存放​​​<property>​​​ 标签中的name和 ref 或者value。
类图如下:
从零开始造Spring02---实现setter注入_java
如果是ref 类型的我们还需要将其实例名保存到​​​RuntimeBeanReference​​​中,如果是value 类型的我们需要将其值保存到​​TypedStringValue​​​ 中
从零开始造Spring02---实现setter注入_java_02

关键代码实例

  1. GenericBeanDefinition 类,存放property的数据结构
public class GenericBeanDefinition implements BeanDefinition{
private String beanClassName;
private List<PropertyValue> propertyValueList = new ArrayList<PropertyValue>();
public String getBeanClassName() {
return this.beanClassName;
}
@Override
public List<PropertyValue> getPropertyValues() {
return this.propertyValueList;
}
}
  1. XmlBeanDefinitionReader 类,主要用于解析xml,读取其中的配置
public class XmlBeanDefinitionReader {

public static final String PROPERTY_ELEMENT = "property";

public static final String REF_ATTRIBUTE = "ref";

public static final String VALUE_ATTRIBUTE = "value";

public static final String NAME_ATTRIBUTE = "name";

public void parsePropertyElement(Element beanElem, BeanDefinition bd) {
Iterator iterator = beanElem.elementIterator(PROPERTY_ELEMENT);
while (iterator.hasNext()) {
Element propElem = (Element) iterator.next();
// 取出name 元素
String propertyName = propElem.attributeValue(NAME_ATTRIBUTE);
// 元素如果为空直接返回
if (!StringUtils.hasLength(propertyName)) {
logger.fatal("Tag 'property' must have a 'name' attribute");
return;
}
Object val = parsePropertyValue(propElem, bd, propertyName);
PropertyValue pv = new PropertyValue(propertyName, val);
bd.getPropertyValues().add(pv);
}
}

public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {
String elementName = (propertyName != null) ?
"<property> element for property '" + propertyName + "'" :
"<constructor-arg> element";
//分别取出ref属性和value属性。
boolean hasRefAttribute = (ele.attribute(REF_ATTRIBUTE) != null);
boolean hasValueAttribute = (ele.attribute(VALUE_ATTRIBUTE) != null);
if (hasRefAttribute) {
String refName = ele.attributeValue(REF_ATTRIBUTE);
if (!StringUtils.hasText(refName)) {
logger.error(elementName + " contains empty 'ref' attribute");
}
RuntimeBeanReference ref = new RuntimeBeanReference(refName);
return ref;
} else if (hasValueAttribute) {
TypedStringValue typedStringValue = new TypedStringValue(ele.attributeValue(VALUE_ATTRIBUTE));
return typedStringValue;

} else {
throw new RuntimeException(elementName + " must specify a ref or value");
}
}

}

读取出来ref 或者value之后,我们如何将其实例化呢?对此我们新建了一个类​​BeanDefinitionValueResolve​​​来处理value 的值。
代码如下:

public class BeanDefinitionValueResolve {
private final BeanFactory beanFactory;

public BeanDefinitionValueResolve(BeanFactory beanFactory) {
this.beanFactory = beanFactory;
}

public Object resolveValueIfNecessary(Object value) {
if (value instanceof RuntimeBeanReference) {
RuntimeBeanReference ref = (RuntimeBeanReference) value;
String refName = ref.getBeanName();
Object bean = this.beanFactory.getBean(refName);
return bean;
} else if (value instanceof TypedStringValue) {
return ((TypedStringValue) value).getValue();
} else {
throw new RuntimeException("the value " + value + " has not implemented");
}
}
}

那么如果获取bean,并且设置属性呢:
关键代码如下:(DefaultBeanFactory类中)

public Object createBean(BeanDefinition bd) {
// 创建实例
Object bean = instantiateBean(bd);
//设置属性
populateBean(bd, bean);
// populateBeanUseCommonBeanUtils(bd,bean);
return bean;
}

private Object instantiateBean(BeanDefinition bd) {
ClassLoader beanClassLoader = this.getBeanClassLoader();
String beanClassName = bd.getBeanClassName();

try {
Class<?> clz = beanClassLoader.loadClass(beanClassName);
return clz.newInstance();
} catch (Exception e) {
throw new BeanCreationException("create bean for "+ beanClassName +" failed",e);
}
}
/**
* 调用set方法进行setter注入
* @param bd
* @param bean
*/
protected void populateBean(BeanDefinition bd, Object bean) {
// 获取一个bean下所有的PropertyValue
List<PropertyValue> pvs = bd.getPropertyValues();
if (pvs == null || pvs.isEmpty()) {
return;
}
// 实例化BeanDefinitionValueResolve,并传入当前的DefaultBeanFactory
BeanDefinitionValueResolve valueResolve = new BeanDefinitionValueResolve(this);
SimpleTypeCoverter coverter = new SimpleTypeCoverter();

try {
for (PropertyValue pv : pvs) {
String propertyName = pv.getName();
//对于ref来说就是beanName,对于value 来说就是value
Object originalValue = pv.getValue();
Object resolvedValue = valueResolve.resolveValueIfNecessary(originalValue);
// 假设现在originalValue表示的是ref=accountDao,已经通过resolve得到了accountDao对象,接下来
// 如何调用petStoreService的setAccountDao方法?
// 注释:使用到了java.beans 中的Introspector类拿到bean的相关信息,包括其属性,方法
BeanInfo beanInfo = Introspector.getBeanInfo(bean.getClass());
PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
for (PropertyDescriptor pd : pds) {
if (pd.getName().equals(propertyName)) {
Object convertedValue = coverter.convertIfNecessary(resolvedValue, pd.getPropertyType());
//通过反射的方式调用set方法
pd.getWriteMethod().invoke(bean, convertedValue);
break;
}
}
}
} catch (Exception e) {
throw new BeanCreationException("Failed to obtain BeanInfo for class["+bd.getBeanClassName()+"]",e);
}

}

调试如下:
从零开始造Spring02---实现setter注入_java_03

类型转化

类图如下:
从零开始造Spring02---实现setter注入_java_04
解析说明:
TypeConverter 类型转化接口,将传入的值转化为其需要的类型。
SimpleTypeCoverter 是TypeConverter接口的一个实现。其依赖于java.beans中的PropertyEditor,其类似于java GUI中的编程,例如:拖拽一个button, 然后,设置其颜色,长度,宽度,这些都属于button的属性,在java.beans中将这些抽象成了一个PropertyEditor 接口。 setAsText(), 例如button 的高度,值是什么跟属性的类型密切相关。

代码示例

public class CustomNumberEditor extends PropertyEditorSupport {
private final Class<? extends Number> numberClass;
private final boolean allowEmpty;
private final NumberFormat numberFormat;

public CustomNumberEditor(Class<? extends Number> numberClass, boolean allowEmpty) {
this(numberClass, allowEmpty,null);
}

public CustomNumberEditor(Class<? extends Number> numberClass, boolean allowEmpty, NumberFormat numberFormat) {
if (numberClass == null || !Number.class.isAssignableFrom(numberClass)) {
throw new IllegalArgumentException("Property class must be a subclass of Number");

}

this.numberClass = numberClass;
this.allowEmpty = allowEmpty;
this.numberFormat = numberFormat;
}

@Override
public void setAsText(String text) throws IllegalArgumentException {
if (this.allowEmpty && !StringUtils.hasText(text)) {
setValue(null);
} else if (this.numberFormat != null) {
setValue(NumberUtils.parseNumber(text, this.numberClass, this.numberFormat));
} else {
setValue(NumberUtils.parseNumber(text, this.numberClass));

}
}

public void setValue(Object value) {
if (value instanceof Number) {
super.setValue(NumberUtils.convertNumberToTargetClass((Number) value, this.numberClass));

} else {
super.setValue(value);
}
}
public String getAsText() {
Object value = getValue();
if (value == null) {
return "";
} else if (this.numberFormat != null) {
return this.numberFormat.format(value);
} else {
return value.toString();
}

}
}

SimpleTypeConverter 类

/**
* 值的类型转化
* @param value 3
* @param requiredType Integer.class
* @param <T>
* @return
* @throws TypeMismatchException
*/
@Override
public <T> T convertIfNecessary(Object value, Class<T> requiredType) throws TypeMismatchException {
// 值能不能直接赋值呢,能,直接返回
if (ClassUtils.isAssignableValue(requiredType, value)) {
return (T) value;
} else {
// 只支持字符串
if (value instanceof String) {
PropertyEditor defaultEditor = findDefaultEditor(requiredType);
try {
defaultEditor.setAsText((String) value);
} catch (IllegalArgumentException e) {
//非法参数异常
throw new TypeMismatchException(value, requiredType);
}
return (T) defaultEditor.getValue();
} else {
throw new RuntimeException("Todo : can't convert value for "+value +" class:"+requiredType);
}

}
}

private PropertyEditor findDefaultEditor(Class<?> requiredType) {
// 查找DefaultEditor
PropertyEditor defaultEditor = this.getDefaultEditor(requiredType);
if (defaultEditor == null) {
throw new RuntimeException("Editor for" + requiredType + "has not been implemented");
}
return defaultEditor;
}

public PropertyEditor getDefaultEditor(Class<?> requiredType) {
if (defaultEditors == null) {
createDefaultEditors();
}
return defaultEditors.get(requiredType);
}

private void createDefaultEditors() {
this.defaultEditors = new HashMap<Class<?>, PropertyEditor>(64);
this.defaultEditors.put(boolean.class, new CustomBooleanEditor(false));
this.defaultEditors.put(Boolean.class, new CustomBooleanEditor(true));
this.defaultEditors.put(int.class, new CustomNumberEditor(Integer.class, false));
this.defaultEditors.put(Integer.class, new CustomNumberEditor(Integer.class, true));

}

———————————-分割线——————————————————–

使用common-beanutil设置bean的属性

说明: Commons BeanUtils 类的
BeanUtils.setProperty(bean, propertyName,propertyValue)
bean : java对象,例如petStoreService
propertyName,例如: “version”,”accountDao”
propertyValue,例如:3, accountDao对象

代码示例

private void populateBeanUseCommonBeanUtils(BeanDefinition bd, Object bean) {
List<PropertyValue> pvs = bd.getPropertyValues();
if (pvs == null || pvs.isEmpty()) {
return;
}
BeanDefinitionValueResolve valueResolve = new BeanDefinitionValueResolve(this);
try {
for (PropertyValue pv : pvs) {
String propertyName = pv.getName();
Object originalValue = pv.getValue();

Object resolve = valueResolve.resolveValueIfNecessary(originalValue);
BeanUtils.copyProperty(bean, propertyName, resolve);

}
} catch (Exception e) {
throw new BeanDefinitionException("Populate bean property failed for["+bd.getBeanClassName()+"");
}


}

———————-答疑总结—————————-

  1. 职责分离的问题:解析的时候只做解析的事,不要做额外的工作。
    从零开始造Spring02---实现setter注入_java_05
  2. Open Close 对修改封闭,对扩展开放,例如:​​AbstractApplicationContext​​。流程定下来了。通过
public abstract Resource getResourceByPath(String configFile);

进行扩展。
3. 单一职责
4. 对接口编程,不对实现编程
5. 优先使用组合。
6. 现在PropertyValue中value有两种类型,是否可以封装成两种PropertyValue
RuntimeBeanReferencePropertyValue和TypedStringValuePropertyValue呢?
答:
1. PropertyValue类中新增一个resolve的抽象方法

public abstract Object resolve(BeanFactory beanFactory);
  1. RuntimeBeanReferencePropertyValue类
public class RuntimeBeanReferencePropertyValue extends PropertyValue {

public RuntimeBeanReferencePropertyValue(String name,String value) {
this.name = name;
this.value = value;
}


@Override
public Object resolve(BeanFactory factory) {
return factory.getBean(name);
}

}
  1. TypedStringValuePropertyValue类
public class TypedStringValuePropertyValue extends PropertyValue {

public TypedStringValuePropertyValue(String name,String value) {
this.name = name;
this.value = value;
}

@Override
public Object resolve(BeanFactory factory) {
return value;
}
}
  1. XmlBeanDefinitionReader中做的修改
public PropertyValue parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {
String elementName = (propertyName != null) ?
"<property> element for property '" + propertyName + "'" :
"<constructor-arg> element";

boolean hasRefAttribute = (ele.attribute(REF_ATTRIBUTE) != null);
boolean hasValueAttribute = (ele.attribute(VALUE_ATTRIBUTE) != null);
if (hasRefAttribute) {
String refName = ele.attributeValue(REF_ATTRIBUTE);
if (!StringUtils.hasText(refName)) {
logger.error(elementName + " contains empty 'ref' attribute");
}
PropertyValue ref = new RuntimeBeanReferencePropertyValue(ele.attributeValue(NAME_ATTRIBUTE),refName);
return ref;
} else if (hasValueAttribute) {
PropertyValue typedStringValue = new TypedStringValuePropertyValue(ele.attributeValue(NAME_ATTRIBUTE),ele.attributeValue(VALUE_ATTRIBUTE));
return typedStringValue;

} else {
throw new RuntimeException(elementName + " must specify a ref or value");
}
}

参考源代码

​​https://github.com/XWxiaowei/spring-learn/releases/tag/testcase-3​​


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