Spring的p标签是基于XML Schema的配置方式，目的是为了简化配置方式。
在XML文件头部添加xmlns:p="http://www.springframework.org/schema/p"即可使用。(在Spring之后的版本中，p标签已经包含到namespace "http://www.w3.org/2000/xmlns/"中了)
例如：
类Person
public class Person
{
private int age;
private Tool tool;
public void setAge(int age)
{
this.age=age;
}
public void setTool(Tool tool)
{
this.tool=tool;
}
其余代码省略
......
}
原本的bean配置为
<?xml version="1.0" encoding="GBK"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
<bean id="person" class="com.myclass.Person">
<property name="age" value="21"/>
<property name="tool" ref="tool"/>
</bean>
</beans>
使用P标签的配置为
<?xml version="1.0" encoding="GBK"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
<bean id="person" class="com.myclass.Person" p:age="21" p:tool-ref="tool"/>
</beans>
http://blog.csdn.net/spirit23k/article/details/8214765
I‘ve created a project with spring mvc and in my dispatcherServlet.xml file
<bean id="jspViewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver"
p:prefix="/WEB-INF/views/"
p:suffix=".jsp"
/>
p:prefix and p:suffix are not allowed. How can I solve this issue? I‘ve used SpringVersion 3.2.3.RELEASE
You need to add the p-namespace declaration: xmlns:p="http://www.springframework.org/schema/p"
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
See Spring reference: Chapter 5.4.2.6 XML shortcut with the p-namespace
http://docs.spring.io/spring/docs/3.2.x/spring-framework-reference/html/beans.html#beans-p-namespace
XML shortcut with the p-namespace
The p-namespace enables you to use the bean element‘s attributes, instead of nested <property/> elements, to describe your property values and/or collaborating beans.
Spring 2.0 and later supports extensible configuration formats with namespaces, which are based on an XML Schema definition. The beans configuration format discussed in this chapter is defined in an XML Schema document. However, the p-namespace is not defined in an XSD file and exists only in the core of Spring.
The following example shows two XML snippets that resolve to the same result: The first uses standard XML format and the second uses the p-namespace.
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean name="classic" class="com.example.ExampleBean">
<property name="email" value="[email protected]"/>
</bean>
<bean name="p-namespace" class="com.example.ExampleBean"
p:email="[email protected]"/>
</beans>
The example shows an attribute in the p-namespace called email in the bean definition. This tells Spring to include a property declaration. As previously mentioned, the p-namespace does not have a schema definition, so you can set the name of the attribute to the property name.
This next example includes two more bean definitions that both have a reference to another bean:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean name="john-classic" class="com.example.Person">
<property name="name" value="John Doe"/>
<property name="spouse" ref="jane"/>
</bean>
<bean name="john-modern"
class="com.example.Person"
p:name="John Doe"
p:spouse-ref="jane"/>
<bean name="jane" class="com.example.Person">
<property name="name" value="Jane Doe"/>
</bean>
</beans>
As you can see, this example includes not only a property value using the p-namespace, but also uses a special format to declare property references. Whereas the first bean definition uses <property name="spouse" ref="jane"/> to create a reference from bean john to bean jane, the second bean definition uses p:spouse-ref="jane" as an attribute to do the exact same thing. In this case spouse is the property name, whereas the -ref part indicates that this is not a straight value but rather a reference to another bean.
 |
Note |
|---|---|
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The p-namespace is not as flexible as the standard XML format. For example, the format for declaring property references clashes with properties that end in Ref, whereas the standard XML format does not. We recommend that you choose your approach carefully and communicate this to your team members, to avoid producing XML documents that use all three approaches at the same time.
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XML shortcut with the c-namespace
Similar to the the section called “XML shortcut with the p-namespace”, the c-namespace, newly introduced in Spring 3.1, allows usage of inlined attributes for configuring the constructor arguments rather then nested constructor-arg elements.
Let‘s review the examples from the section called “Constructor-based dependency injection” with the c namespace:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:c="http://www.springframework.org/schema/c"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="bar" class="x.y.Bar"/>
<bean id="baz" class="x.y.Baz"/>
<-- ‘traditional‘ declaration -->
<bean id="foo" class="x.y.Foo">
<constructor-arg ref="bar"/>
<constructor-arg ref="baz"/>
<constructor-arg value="[email protected]"/>
</bean>
<-- ‘c-namespace‘ declaration -->
<bean id="foo" class="x.y.Foo" c:bar-ref="bar" c:baz-ref="baz" c:email="[email protected]">
</beans>
The c: namespace uses the same conventions as the p: one (trailing -ref for bean references) for setting the constructor arguments by their names. And just as well, it needs to be declared even though it is not defined in an XSD schema (but it exists inside the Spring core).
For the rare cases where the constructor argument names are not available (usually if the bytecode was compiled without debugging information), one can use fallback to the argument indexes:
<-- ‘c-namespace‘ index declaration --> <bean id="foo" class="x.y.Foo" c:_0-ref="bar" c:_1-ref="baz">
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Note |
|---|---|
|
Due to the XML grammar, the index notation requires the presence of the leading _ as XML attribute names cannot start with a number (even though some IDE allow it). |
In practice, the constructor resolution mechanism is quite efficient in matching arguments so unless one really needs to, we recommend using the name notation through-out your configuration.
Compound property names
You can use compound or nested property names when you set bean properties, as long as all components of the path except the final property name are not null. Consider the following bean definition.
<bean id="foo" class="foo.Bar"> <property name="fred.bob.sammy" value="123" /> </bean>
The foo bean has a fred property, which has a bob property, which has a sammy property, and that final sammy property is being set to the value 123. In order for this to work, thefred property of foo, and the bob property of fred must not be null after the bean is constructed, or a NullPointerException is thrown.
5.4.3 Using depends-on
If a bean is a dependency of another that usually means that one bean is set as a property of another. Typically you accomplish this with the <ref/> element in XML-based configuration metadata. However, sometimes dependencies between beans are less direct; for example, a static initializer in a class needs to be triggered, such as database driver registration. The depends-on attribute can explicitly force one or more beans to be initialized before the bean using this element is initialized. The following example uses the depends-on attribute to express a dependency on a single bean:
<bean id="beanOne" class="ExampleBean" depends-on="manager"/> <bean id="manager" class="ManagerBean" />
To express a dependency on multiple beans, supply a list of bean names as the value of the depends-on attribute, with commas, whitespace and semicolons, used as valid delimiters:
<bean id="beanOne" class="ExampleBean" depends-on="manager,accountDao"> <property name="manager" ref="manager" /> </bean> <bean id="manager" class="ManagerBean" /> <bean id="accountDao" class="x.y.jdbc.JdbcAccountDao" />
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Note |
|---|---|
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The depends-on attribute in the bean definition can specify both an initialization time dependency and, in the case of singleton beans only, a corresponding destroy time dependency. Dependent beans that define a depends-on relationship with a given bean are destroyed first, prior to the given bean itself being destroyed. Thus depends-on can also control shutdown order.
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5.4.4 Lazy-initialized beans
By default, ApplicationContext implementations eagerly create and configure all singleton beans as part of the initialization process. Generally, this pre-instantiation is desirable, because errors in the configuration or surrounding environment are discovered immediately, as opposed to hours or even days later. When this behavior is notdesirable, you can prevent pre-instantiation of a singleton bean by marking the bean definition as lazy-initialized. A lazy-initialized bean tells the IoC container to create a bean instance when it is first requested, rather than at startup.
In XML, this behavior is controlled by the lazy-init attribute on the <bean/> element; for example:
<bean id="lazy" class="com.foo.ExpensiveToCreateBean" lazy-init="true"/> <bean name="not.lazy" class="com.foo.AnotherBean"/>
When the preceding configuration is consumed by an ApplicationContext, the bean named lazy is not eagerly pre-instantiated when the ApplicationContext is starting up, whereas the not.lazy bean is eagerly pre-instantiated.
However, when a lazy-initialized bean is a dependency of a singleton bean that is not lazy-initialized, the ApplicationContext creates the lazy-initialized bean at startup, because it must satisfy the singleton‘s dependencies. The lazy-initialized bean is injected into a singleton bean elsewhere that is not lazy-initialized.
You can also control lazy-initialization at the container level by using the default-lazy-init attribute on the <beans/> element; for example:
<beans default-lazy-init="true"> <!-- no beans will be pre-instantiated... --> </beans>
http://www.cnblogs.com/huey/p/4507122.html