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The <property> elements in Listing 2-5 specify the setter injections on bean properties. These properties are defined in the JavaBean specifications and are typically used to read and assign class member variables. The method names and types in the getter and setter methods must match. The property names in the XML file refer to this name, although the first letter of the property name must be lowercase. For example, the setFullName() method becomes fullName, the setRanking() method becomes ranking, and so on. To set a property with the Spring container, you need at least a setter method, as shown in Listing 2-6. Listing 2-6. Write-Only JavaBean Properties Have Only Setter Methods package com.apress.springbook.chapter02; public class Player { private String fullName; private int ranking; public void setFullName(String fullName) { this.fullName = fullName; } public void setRanking(int ranking) { this.ranking = ranking; } } You can optionally add a getter method to make the property readable, as shown in Listing 2-7, but this is not required by the container. Listing 2-7. Adding a Getter Method to Make the JavaBean Property Readable package com.apress.springbook.chapter02; public class Player { private String fullName; private int ranking; public void setFullName(String fullName) { this.fullName = fullName; }

public void setRanking(int ranking) { this.ranking = ranking; } public String getFullName() { return this.fullName; } public int getRanking() { return this.ranking; } } Setter injection can inject values and other beans, as shown in Listing 2-8. Listing 2-8. Injecting Values and Other Beans via Setter Methods < xml version="1.0" encoding="UTF-8" > <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd"> <beans> <bean id="Kim" class="com.apress.springbook.chapter02.Player"> <property name="fullName" value="Kim Clijsters"/> <property name="ranking" value="1"/> </bean> <bean id="Justine" class="com.apress.springbook.chapter02.Player"> <property name="fullName" ref="Henin-Hardenne"/> <property name="ranking" value="5"/> </bean> <bean id="Henin-Hardenne" class="java.lang.String"> <constructor-arg value="Justine Henin-Hardenne"/> </bean> </beans> The value attribute injects a literal value from the XML file, and the ref attribute injects another bean. This example creates a java.lang.String bean, indicating that the container can instantiate any class.

We ll rewrite the Player class to use constructor injection, as shown in Listing 2-9. Listing 2-9. The Player Class, Which Takes Its Internal State via the Constructor package com.apress.springbook.chapter02; public class Player { private String fullName; private int ranking; public Player(String fullName, int ranking) { if (fullName == null || fullName.length() == 0) { throw new IllegalArgumentException("Full name is required!"); } this.fullName = fullName;

this.ranking = ranking; } public String getFullName() { return this.fullName; } public int getRanking() { return this.ranking; } } By refactoring the Player class, we ve introduced one significant change by making the full name required. Checking the state of the object is the most important reason that developers create constructors in their classes. Listing 2-10 shows how the container is instructed to call the constructor. Listing 2-10. Instructing the Container to Call the Player Constructor < xml version="1.0" encoding="UTF-8" > <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd"> <beans> <bean id="Kim" class="com.apress.springbook.chapter02.Player"> <constructor-arg value="Kim Clijsters"/> <constructor-arg value="1"/> </bean> <bean id="Justine" class="com.apress.springbook.chapter02.Player"> <constructor-arg ref="Henin-Hardenne"/> <constructor-arg value="5"/> </bean> <bean id="Henin-Hardenne" class="java.lang.String"> <constructor-arg value="Justine Henin-Hardenne"/> </bean> </beans> The container must choose which constructor it will invoke based on the information in the bean definition. For the configuration in Listing 2-10, the behavior is predictable since the Player class defines only one constructor. Listing 2-11 shows an example that includes two constructors.

In Java, the names of constructor arguments cannot be retrieved from compiled classes by the Reflection API. Other tools, like the open source ASM framework, can retrieve constructor argument names by looking at debug information in the compiled bytecode. However, at the time of this writing, the container does not take the name of arguments into account when invoking constructors.

Listing 2-11. The ConstructorTestBean Class, Which Has Two Constructors package com.apress.springbook.chapter02; public class ConstructorTestBean { private boolean constructor1Used = false; private boolean constructor2Used = false;