spring源码探究---beanFactory为bean对象设置属性时涉及到的类型转换

自己想着实现一个简单点的类似Spring的beanFactory，解析下xml，通过反射调用相关的set方法来实现构建bean对象，其间遇到一个问题没找到比较好的解决方案。

现在有一个简单的bean：

public class MyBean
{
	private int id;

	public int getId()
	{
		return id;
	}

	public void setId(int id)
	{
		this.id = id;
	}
}

然后有一个简单的beans.xml

<beans>
	<bean id="myBean" class="com.iss.bean.MyBean">
		<property name="id" value="1"></property>
	</bean>
</beans>

从xml解析得到一个属性value后，是字符串类型，然后要转换成set方法的参数类型，

但是如果编译时无法得知set参数的类型，就像spring那样在运行时动态获取类型动态转换，该如何实现。

也曾想过一个个比对，但是感觉太复杂，也许有简单点的方法。

然后开始艰辛地调试spring源码….

Spring在解析了xml之后会将所有属性值与属性名存储在对应bean的PropertyValues中，

该结构维护了一个List<PropertyValue> propertyValueList，而PropertyValue则维护着单个属性的属性名和属性值。

然后通过遍历该propertyValueList，将每一个待转换的类型进行判断并转换。

在获取到bean类和属性名后，spring通过该属性的get方法的返回类型或者set方法的参数类型得到属性类型，下面即获取类型

// org.springframework.beans .GenericTypeAwarePropertyDescriptor.class
public synchronized Class getPropertyType() {
		if (this.propertyType == null) {
			if (this.readMethod != null) {
				this.propertyType = GenericTypeResolver.resolveReturnType(this.readMethod, this.beanClass);//这里的readMethod就是get方法
			}
			else {
				MethodParameter writeMethodParam = getWriteMethodParameter();//获取到set方法的参数
				if (writeMethodParam != null) {
					this.propertyType = writeMethodParam.getParameterType();
				}
				else {
					this.propertyType = super.getPropertyType();
				}
			}
		}
		return this.propertyType;
	}

下面是做类型转换一些操作，首先需要根据类型获得一个对应的Editor,原生数据类型都会使用装箱类的Editor

//在org.springframework.beans.PropertyEditorRegistrySupport.class
private void createDefaultEditors() {
		this.defaultEditors = new HashMap<Class<?>, PropertyEditor>(64);

		// Simple editors, without parameterization capabilities.
		// The JDK does not contain a default editor for any of these target types.
		this.defaultEditors.put(Charset.class, new CharsetEditor());
		this.defaultEditors.put(Class.class, new ClassEditor());
		this.defaultEditors.put(Class[].class, new ClassArrayEditor());
		this.defaultEditors.put(Currency.class, new CurrencyEditor());
		this.defaultEditors.put(File.class, new FileEditor());
		this.defaultEditors.put(InputStream.class, new InputStreamEditor());
		this.defaultEditors.put(InputSource.class, new InputSourceEditor());
		this.defaultEditors.put(Locale.class, new LocaleEditor());
		this.defaultEditors.put(Pattern.class, new PatternEditor());
		this.defaultEditors.put(Properties.class, new PropertiesEditor());
		this.defaultEditors.put(Resource[].class, new ResourceArrayPropertyEditor());
		this.defaultEditors.put(TimeZone.class, new TimeZoneEditor());
		this.defaultEditors.put(URI.class, new URIEditor());
		this.defaultEditors.put(URL.class, new URLEditor());
		this.defaultEditors.put(UUID.class, new UUIDEditor());

		// Default instances of collection editors.
		// Can be overridden by registering custom instances of those as custom editors.
		this.defaultEditors.put(Collection.class, new CustomCollectionEditor(Collection.class));
		this.defaultEditors.put(Set.class, new CustomCollectionEditor(Set.class));
		this.defaultEditors.put(SortedSet.class, new CustomCollectionEditor(SortedSet.class));
		this.defaultEditors.put(List.class, new CustomCollectionEditor(List.class));
		this.defaultEditors.put(SortedMap.class, new CustomMapEditor(SortedMap.class));

		// Default editors for primitive arrays.
		this.defaultEditors.put(byte[].class, new ByteArrayPropertyEditor());
		this.defaultEditors.put(char[].class, new CharArrayPropertyEditor());

		// The JDK does not contain a default editor for char!
		this.defaultEditors.put(char.class, new CharacterEditor(false));
		this.defaultEditors.put(Character.class, new CharacterEditor(true));

		// Spring's CustomBooleanEditor accepts more flag values than the JDK's default editor.
		this.defaultEditors.put(boolean.class, new CustomBooleanEditor(false));
		this.defaultEditors.put(Boolean.class, new CustomBooleanEditor(true));

		// The JDK does not contain default editors for number wrapper types!
		// Override JDK primitive number editors with our own CustomNumberEditor.
		this.defaultEditors.put(byte.class, new CustomNumberEditor(Byte.class, false));
		this.defaultEditors.put(Byte.class, new CustomNumberEditor(Byte.class, true));
		this.defaultEditors.put(short.class, new CustomNumberEditor(Short.class, false));
		this.defaultEditors.put(Short.class, new CustomNumberEditor(Short.class, true));
		this.defaultEditors.put(int.class, new CustomNumberEditor(Integer.class, false));
		this.defaultEditors.put(Integer.class, new CustomNumberEditor(Integer.class, true));
		this.defaultEditors.put(long.class, new CustomNumberEditor(Long.class, false));
		this.defaultEditors.put(Long.class, new CustomNumberEditor(Long.class, true));
		this.defaultEditors.put(float.class, new CustomNumberEditor(Float.class, false));
		this.defaultEditors.put(Float.class, new CustomNumberEditor(Float.class, true));
		this.defaultEditors.put(double.class, new CustomNumberEditor(Double.class, false));
		this.defaultEditors.put(Double.class, new CustomNumberEditor(Double.class, true));
		this.defaultEditors.put(BigDecimal.class, new CustomNumberEditor(BigDecimal.class, true));
		this.defaultEditors.put(BigInteger.class, new CustomNumberEditor(BigInteger.class, true));

		// Only register config value editors if explicitly requested.
		if (this.configValueEditorsActive) {
			StringArrayPropertyEditor sae = new StringArrayPropertyEditor();
			this.defaultEditors.put(String[].class, sae);
			this.defaultEditors.put(short[].class, sae);
			this.defaultEditors.put(int[].class, sae);
			this.defaultEditors.put(long[].class, sae);
		}
	}

通过上面的代码可以看出假如此时的属性类型为int等则Editor为CustomNumberEditor，其他类似，

然后调用不同的Editor的setAsText方法将从xml解析得到的String类型转换成对应类型

比如下面的Number的转换

// org.springframework.beans.propertyeditors. CustomNumberEditor.class
public void setAsText(String text) throws IllegalArgumentException {
		if (this.allowEmpty && !StringUtils.hasText(text)) {
			// Treat empty String as null value.
			setValue(null);
		}
		else if (this.numberFormat != null) {
			// Use given NumberFormat for parsing text.
			setValue(NumberUtils.parseNumber(text, this.numberClass, this.numberFormat));
		}
		else {
			// Use default valueOf methods for parsing text.
			setValue(NumberUtils.parseNumber(text, this.numberClass));
		}
	}

最终可以看到，spring的处理方式还是比对class对象再做类型转换，

只不过spring做了一个更好的管理，将Number的放在一起，其他的不同类型都单独考虑，不知道还有没更加方便的转换方法

// org.springframework.util.NumberUtils.class
public static <T extends Number> T parseNumber(String text, Class<T> targetClass) {
		Assert.notNull(text, "Text must not be null");
		Assert.notNull(targetClass, "Target class must not be null");
		String trimmed = StringUtils.trimAllWhitespace(text);

		if (targetClass.equals(Byte.class)) {
			return (T) (isHexNumber(trimmed) ? Byte.decode(trimmed) : Byte.valueOf(trimmed));
		}
		else if (targetClass.equals(Short.class)) {
			return (T) (isHexNumber(trimmed) ? Short.decode(trimmed) : Short.valueOf(trimmed));
		}
		else if (targetClass.equals(Integer.class)) {
			return (T) (isHexNumber(trimmed) ? Integer.decode(trimmed) : Integer.valueOf(trimmed));
		}
		else if (targetClass.equals(Long.class)) {
			return (T) (isHexNumber(trimmed) ? Long.decode(trimmed) : Long.valueOf(trimmed));
		}
		else if (targetClass.equals(BigInteger.class)) {
			return (T) (isHexNumber(trimmed) ? decodeBigInteger(trimmed) : new BigInteger(trimmed));
		}
		else if (targetClass.equals(Float.class)) {
			return (T) Float.valueOf(trimmed);
		}
		else if (targetClass.equals(Double.class)) {
			return (T) Double.valueOf(trimmed);
		}
		else if (targetClass.equals(BigDecimal.class) || targetClass.equals(Number.class)) {
			return (T) new BigDecimal(trimmed);
		}
		else {
			throw new IllegalArgumentException(
					"Cannot convert String [" + text + "] to target class [" + targetClass.getName() + "]");
		}
	}