Spring详细内容En（2）

电玩女神 2023-09-24 18:39 54阅读 0赞

# 1.Constructor Injection with Dependent Object #

*  If there is `HAS-A relationship` between the classes, we create the instance of dependent object (contained object) first then pass it as an argument of the main class constructor.
 *  Here, our scenario is Employee HAS-A Address. The Address class object will be termed as the dependent object.

## **Address.java** ##

This class contains three properties, one constructor and toString() method to return the values of these object.

public class Address {
        
        private String city;
        private String state;
        private String country;
    
        public Address(String city, String state, String country) {
        
            this.city = city;
            this.state = state;
            this.country = country;
        }
        public String toString(){
        
            return city+" "+state+" "+country;
        }
    }

## **Employee.java** ##

It contains three properties id, name and address(**dependent object**) ,two constructors and show() method to **show the records of the current object including the depedent object.**

public class Employee {
        
        private int id;
        private String name;
        private Address address;
    
        public Employee(int id, String name, Address address) {
        
            this.id = id;
            this.name = name;
            this.address = address;
        }
        void show(){
        
            System.out.println(id+" "+name);
            System.out.println(address.toString());
        }
    }

## **applicationContext.xml** ##

The`ref` attribute is used to **define the reference of another object**, such way we are passing the dependent object as an constructor argument.

## **Test.java** ##

This class gets the bean from the `applicationContext.xml` file and calls the show method.

public class Test1 {
        
        public static void main(String[] args) {
        
            Resource resource = new ClassPathResource("applicationContext.xml");
            BeanFactory factory = new XmlBeanFactory(resource);
            Employee employee = (Employee) factory.getBean("employee");
            employee.show();
    
        }
    }

1 Amy
    Suzhou Jangsu China

# 2.Constructor Injection with Collection Example #

*  We can `inject collection values` by `constructor`in spring framework.
 *  There can be used `three elements inside the constructor-arg element`.
    
     *  list
     *  set
     *  map

## Question.java ##

public class Question {
        
        private int id;
        private String name;
        private List<String> answers;
    
        public Question(int id, String name, List<String> answers) {
        
            this.id = id;
            this.name = name;
            this.answers = answers;
        }
        public void displayInfo(){
        
            System.out.println(id+" "+name);
            Iterator<String> itr = answers.iterator();
            while(itr.hasNext()){
        
                System.out.println(itr.next());
            }
        }
    }

## applicationContext.xml ##

The list element of constructor-arg is used here to define the `list`.

## Test.java ##

public class Test {
        
        public static void main(String[] args) {
        
            Resource resource = new ClassPathResource("applicationContext.xml");
            BeanFactory factory = new XmlBeanFactory(resource);
            Question question= (Question) factory.getBean("question");
            question.displayInfo();
        }
    }

1 Amy
    Java is a programming language
    Java is a Platform

# 3.Constructor Injection with Non-String Collection (having Dependent Object) Example #

*  If we **have dependent object in the collection**, we can inject these information by using the **ref element inside the list, set or map**.
 *  In this example, we are taking the example of Forum where **One question can have multiple answers**.

## Question.java ##

This class contains three properties, **two constructors and displayInfo() method** that prints the information. Here, we are **using List to contain the multiple answers**.

public class Question {
        
        private int id;
        private String name;
        private List<Answer> answers;
    
        public Question() {
        
        }
    
        public Question(int id, String name, List<Answer> answers) {
        
            this.id = id;
            this.name = name;
            this.answers = answers;
        }
    
        public void displayInfo(){
        
            System.out.println(id+" "+name);
            Iterator<Answer> itr = answers.iterator();
            while(itr.hasNext()){
        
                System.out.println(itr.next());
            }
        }
    }

## Answer.java ##

This class has three properties id, name and by with constructor and toString() method.

public class Answer {
        
        private int id;
        private String name;
        private String by;
        public Answer(){
        }
    
        public Answer(int id, String name, String by) {
        
            super();
            this.id = id;
            this.name = name;
            this.by = by;
        }
        public String toString(){
        
            return id+" "+name+" "+by;
        }
    }

## applicationContext.xml ##

The `ref`element is used to define the reference of another bean. Here, we are using `bean` attribute of `ref` element to specify the reference of another bean.

<?xml version="1.0" encoding="UTF-8"?>
    <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="ans1" class="com.amy.Answer">
            <constructor-arg value="1" type="int"></constructor-arg>
            <constructor-arg value="Ste" type="String"></constructor-arg>
            <constructor-arg value="Java is a programming language" type="String"></constructor-arg>
        </bean>
        <bean id="ans2" class="com.amy.Answer">
            <constructor-arg value="2" type="int"></constructor-arg>
            <constructor-arg value="David" type="String"></constructor-arg>
            <constructor-arg value="Java is a Platform" type="String"></constructor-arg>
        </bean>
    
        <bean id="question" class="com.amy.Question">
            <constructor-arg value="1" type="int"></constructor-arg>
            <constructor-arg value="Amy" type="String"></constructor-arg>
            <constructor-arg>
                <list>
                    <ref bean="ans1"/>
                    <ref bean="ans2"/>
                </list>
            </constructor-arg>
    
        </bean>
    </beans>

## Test.java ##

1 Amy
    1 Ste Java is a programming language
    2 David Java is a Platform

# 4.Constructor Injection with Non-String Map (having dependent Object) Example #

*  In this example, we are **using map** as the answer that have Answer and User.
 *  Here, we are using key and value pair both as an object. `Answer`has its own information such as `answerId, answer and postedDate`, `User`has its own information such as`userId, username, emailId`.

public class User {
        
        private int id;
        private String name,email;
        public User(){
        }
    
        public User(int id, String name, String email) {
        
            this.id = id;
            this.name = name;
            this.email = email;
        }
    
        @Override
        public String toString() {
        
            return "Id:"+id+" Name:"+name+" Email Id:"+email;
        }
    }

public class Question {
        
        private int id;
        private String name;
        private Map<Answer,User> answers;
    
        public Question() {
        
        }
    
        public Question(int id, String name, Map<Answer,User> answers) {
        
            this.id = id;
            this.name = name;
            this.answers = answers;
        }
    
        public void displayInfo(){
        
            System.out.println("question id:"+id);
            System.out.println("question name:"+name);
            System.out.println("Answers....");
            Set<Map.Entry<Answer,User>> set= answers.entrySet();
    
            Iterator<Map.Entry<Answer,User>> itr = set.iterator();
            while(itr.hasNext()){
        
                Map.Entry<Answer,User> entry = itr.next();
                Answer ans = entry.getKey();
                User user = entry.getValue();
                System.out.println("Answer Information:");
                System.out.println(ans);
                System.out.println("Posted By:");
                System.out.println(user);
            }
        }
    }

<?xml version="1.0" encoding="UTF-8"?>
    <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="ans1" class="com.amy.Answer">
            <constructor-arg value="1" ></constructor-arg>
            <constructor-arg value="Java is a Programming Language"></constructor-arg>
            <constructor-arg value="12/12/2001"></constructor-arg>
        </bean>
        <bean id="user1" class="com.amy.User">
            <constructor-arg value="1" ></constructor-arg>
            <constructor-arg value="Ste" ></constructor-arg>
            <constructor-arg value="Ste@gmail.com" ></constructor-arg>
        </bean>
        <bean id="ans2" class="com.amy.Answer">
            <constructor-arg value="2" type="int"></constructor-arg>
            <constructor-arg value="Java is a Platform" type="String"></constructor-arg>
            <constructor-arg value="12/12/2003" type="String"></constructor-arg>
        </bean>
        <bean id="user2" class="com.amy.User">
            <constructor-arg value="2" ></constructor-arg>
            <constructor-arg value="LiLi" ></constructor-arg>
            <constructor-arg value="LiLi@gmail.com" ></constructor-arg>
        </bean>
    
        <bean id="question" class="com.amy.Question">
            <constructor-arg value="1" type="int"></constructor-arg>
            <constructor-arg value="What is Java?"></constructor-arg>
            <constructor-arg>
                <map>
                    <entry key-ref ="ans1" value-ref="user1"/>
                    <entry key-ref="ans2" value-ref="user2" />
                </map>
            </constructor-arg>
    
        </bean>
    </beans>

# 5.Inheriting Bean in Spring #

*  By using the `parent` attribute of `bean`, we can specify the `inheritance` relation between the beans. In such case, parent bean values will be inherited to the current bean.

public class Employee {
        
        private int id;
        private String name;
        private Address address;
    
        public Employee() {
        
        }
    
        public Employee(int id, String name) {
        
            this.id = id;
            this.name = name;
        }
    
        public Employee(int id, String name, Address address) {
        
            this.id = id;
            this.name = name;
            this.address = address;
        }
    
        void show(){
        
            System.out.println(id+" "+name);
            System.out.println(address.toString());
        }
    }

package com.amy;
    
    import org.springframework.beans.factory.BeanFactory;
    import org.springframework.beans.factory.xml.XmlBeanFactory;
    import org.springframework.core.io.ClassPathResource;
    import org.springframework.core.io.Resource;
    
    /**
     * @author: Amy
     * @create: 2023-02-14 16:13
     **/
    public class Test1 {
        
        public static void main(String[] args) {
        
            Resource resource = new ClassPathResource("applicationContext.xml");
            BeanFactory factory = new XmlBeanFactory(resource);
            Employee employee = (Employee) factory.getBean("employee");
            employee.show();
    
        }
    }

1 Ste
    Ghaziabad UP USA

# 6.Dependency Injection by setter method #

*  We can `inject the dependency` by `setter method` also.
 *  The `<property>` subelement of `<bean>` is used for setter injection.
    
     *  primitive and String-based values
     *  Dependent object (contained object)
     *  Collection values etc.

## Injecting primitive and string-based values by setter method ##

public class Employee {
        
        private int id;
        private String name;
        private String city;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public String getCity() {
        
            return city;
        }
    
        public void setCity(String city) {
        
            this.city = city;
        }
        void display(){
        
            System.out.println(id + " "+ name+" "+city);
        }
    }

1 Amy Shanghai

## Setter Injection `with Dependent Object`Example ##

public class Employee {
        
        private int id;
        private String name;
        private Address address;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public Address getAddress() {
        
            return address;
        }
    
        public void setAddress(Address address) {
        
            this.address = address;
        }
    
        void display(){
        
            System.out.println(id+" "+name);
            System.out.println(address);
        }
    }

public class Address {
        
        private String city;
        private String state;
        private String country;
    
        public String getCity() {
        
            return city;
        }
    
        public void setCity(String city) {
        
            this.city = city;
        }
    
        public String getState() {
        
            return state;
        }
    
        public void setState(String state) {
        
            this.state = state;
        }
    
        public String getCountry() {
        
            return country;
        }
    
        public void setCountry(String country) {
        
            this.country = country;
        }
    
        public String toString(){
        
            return city+" "+state+" "+country;
        }
    }

1 Amy
    Ghaziabad UP India

## Setter Injection with Collection Example ##

*  We can inject collection values by `setter method`in spring framework. There can be used `three elements`inside the `property element`.
 *  It can be:
    
     *  list
     *  set
     *  map
 *  Each collection can have `string` based and`non-string`based values.

package com.amy;
    
    import java.util.Iterator;
    import java.util.List;
    import java.util.Map;
    import java.util.Set;
    
    /**
     * @author: Amy
     * @create: 2023-02-15 18:39
     **/
    public class Question {
        
        private int id;
        private String name;
        private  List<String> answers;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public List<String> getAnswers() {
        
            return answers;
        }
    
        public void setAnswers(List<String> answers) {
        
            this.answers = answers;
        }
        public void displayInfo(){
        
            System.out.println(id+" "+name);
            System.out.println("answers are:");
            Iterator<String> itr=answers.iterator();
            while(itr.hasNext()){
        
                System.out.println(itr.next());
            }
        }
    }

package com.amy;
    
    import org.springframework.beans.factory.BeanFactory;
    import org.springframework.beans.factory.xml.XmlBeanFactory;
    import org.springframework.core.io.ClassPathResource;
    import org.springframework.core.io.Resource;
    
    
    /**
     * @author: Amy
     * @create: 2023-02-14 14:39
     **/
    public class Test {
        
        public static void main(String[] args) {
        
            Resource resource = new ClassPathResource("applicationContext.xml");
            BeanFactory factory = new XmlBeanFactory(resource);
            Question question= (Question) factory.getBean("question");
            question.displayInfo();
        }
    }

1 "What is Java?"
    answers are:
    Java is a programming language
    Java is a platform
    Java is an Island

## Setter Injection with Non-String Collection (having Dependent Object) Example ##

*  If we have dependent object in the collection, we can inject these information by `using the ref element` inside the `list, set or map`.
 *  Here, we will use list, set or map element inside the property element.

public class Answer {
        
        private int id;
        private String name;
        private String by;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public String getBy() {
        
            return by;
        }
    
        public void setBy(String by) {
        
            this.by = by;
        }
    
        public String toString(){
        
            return id+" "+name+" "+by;
        }
    }

public class Question {
        
        private int id;
        private String name;
        private  List<Answer> answers;;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public List<Answer> getAnswers() {
        
            return answers;
        }
    
        public void setAnswers(List<Answer> answers) {
        
            this.answers = answers;
        }
    
        public void displayInfo(){
        
            System.out.println(id+" "+name);
            Iterator<Answer> itr = answers.iterator();
            while(itr.hasNext()){
        
                System.out.println(itr.next());
            }
        }
    }

<?xml version="1.0" encoding="UTF-8"?>
    <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="answer1" class="com.amy.Answer">
            <property name="id" value="1"></property>
            <property name="name" value="Java is a programming language"></property>
            <property name="by" value="Ravi Malik"></property>
        </bean>
        <bean id="answer2" class="com.amy.Answer">
            <property name="id" value="2"></property>
            <property name="name" value="Java is a platform"></property>
            <property name="by" value="Sachin"></property>
        </bean>
    
        <bean id="question" class="com.amy.Question" >
           <property name="id">
               <value>1</value>
           </property>
            <property name="name">
                <value>"What is Java?"</value>
            </property>
            <property name="answers">
                <list>
                  <ref bean="answer1"></ref>
                  <ref bean="answer2"></ref>
                </list>
            </property>
        </bean>
    </beans>

1 "What is Java?"
    answers are:
    1 Java is a programming language Ravi Malik
    2 Java is a platform Sachin

## Setter Injection with Map Example ##

*  In this example, we are using map as the answer for a question that have `answer` as the `key` and `username` as the `value`.
 *  Here, we are using`key` and `value` pair both as a string.

Like previous examples, it is the example of forum where `one question can have multiple answers`.

public class Question {
        
        private int id;
        private String name;
        private Map<String,String> answers;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public Map<String, String> getAnswers() {
        
            return answers;
        }
    
        public void setAnswers(Map<String, String> answers) {
        
            this.answers = answers;
        }
    
        public void displayInfo(){
        
            System.out.println("question id:"+id);
            System.out.println("question name:"+name);
            System.out.println("Answers....");
            Set<Map.Entry<String, String>> set=answers.entrySet();
            Iterator<Map.Entry<String, String>> itr=set.iterator();
            while(itr.hasNext()){
        
                Map.Entry<String,String> entry=itr.next();
                System.out.println("Answer:"+entry.getKey()+" Posted By:"+entry.getValue());
            }
        }
    }

question id:1
    question name:"What is Java?"
    Answers....
    Answer: Java is a programming language Posted By:Amy
    Answer:Java is a Platform  Posted By:LiLi

## Setter Injection with Non-String Map (having dependent Object) ##

*  In this example, we are using `map` as the`answer` that have Answer and User.
 *  Here, we are`using key and value pair both as an object`.
 *  `Answe`r has its own information such as `answerId, answer and postedDate`, `User` has its own information such as `userId, username, emailId`.

public class Question {
        
        private int id;
        private String name;
        private Map<Answer,User> answers;;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public Map<Answer, User> getAnswers() {
        
            return answers;
        }
    
        public void setAnswers(Map<Answer, User> answers) {
        
            this.answers = answers;
        }
    
        public void displayInfo(){
        
            System.out.println("question id:"+id);
            System.out.println("question name:"+name);
            System.out.println("Answers....");
            Set<Map.Entry<Answer, User>> set=answers.entrySet();
            Iterator<Map.Entry<Answer, User>> itr=set.iterator();
            while(itr.hasNext()){
        
                Map.Entry<Answer, User> entry=itr.next();
                Answer ans=entry.getKey();
                User user=entry.getValue();
                System.out.println("Answer Information:");
                System.out.println(ans);
                System.out.println("Posted By:");
                System.out.println(user);
            }
        }
    }

public class Answer {
        
        private int id;
        private String answer;
    
        public String getPostedDate() {
        
            return postedDate;
        }
    
        public void setPostedDate(String postedDate) {
        
            this.postedDate = postedDate;
        }
    
        private String postedDate;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getAnswer() {
        
            return answer;
        }
    
        public void setAnswer(String answer) {
        
            this.answer = answer;
        }
    
    
        public String toString(){
        
            return id+" "+ answer +" "+postedDate;
        }
    }

public class User {
        
        private int id;
        private String name,email;
    
        public int getId() {
        
            return id;
        }
    
        public void setId(int id) {
        
            this.id = id;
        }
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public String getEmail() {
        
            return email;
        }
    
        public void setEmail(String email) {
        
            this.email = email;
        }
    
        @Override
        public String toString() {
        
            return "Id:"+id+" Name:"+name+" Email Id:"+email;
        }
    }

<?xml version="1.0" encoding="UTF-8"?>
    <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="answer1" class="com.amy.Answer">
            <property name="id" value="1"></property>
            <property name="answer" value="Java is a Programming Language"></property>
            <property name="postedDate" value="12/12/2001"></property>
        </bean>
        <bean id="answer2" class="com.amy.Answer">
            <property name="id" value="2"></property>
            <property name="answer" value="Java is a Platform"></property>
            <property name="postedDate" value="12/12/2003"></property>
        </bean>
    
        <bean id="user1" class="com.amy.User">
            <property name="id" value="1"></property>
            <property name="name" value="Arun Kumar"></property>
            <property name="email" value="arun@gmail.com"></property>
        </bean>
        <bean id="user2" class="com.amy.User">
            <property name="id" value="2"></property>
            <property name="name" value="Varun Kumar"></property>
            <property name="email" value="Varun@gmail.com"></property>
        </bean>
    
        <bean id="question" class="com.amy.Question">
            <property name="id" value="1"></property>
            <property name="name" value="What is Java?"></property>
            <property name="answers">
                <map>
                    <entry key-ref="answer1" value-ref="user1"></entry>
                    <entry key-ref="answer2" value-ref="user2"></entry>
                </map>
            </property>
        </bean>
    </beans>

question id:1
    question name:What is Java?
    Answers....
    Answer Information:
    1 Java is a Programming Language 12/12/2001
    Posted By:
    Id:1 Name:Arun Kumar Email Id:arun@gmail.com
    Answer Information:
    2 Java is a Platform 12/12/2003
    Posted By:
    Id:2 Name:Varun Kumar Email Id:Varun@gmail.com

# 7.Difference between constructor and setter injection #

1.  `Partial dependency`:

*  it can be injected using setter injection but it is **not possible by constructor**.
 *  Suppose there are **3 properties** in a class, having **3 arg constructor and setters methods**.
 *  In such case, if you want to pass information for only one property, it is possible by`setter method only`.

1.  `Overriding`:

*  `Setter injection` overrides the constructor injection.
 *  If we use both `constructor and setter injection`, `IOC container` will use the `setter injection`.

1.  `Changes`:

*  We can easily `change the value by setter injection`.
 *  It doesn’t create a new bean instance always like constructor.
 *  So `setter injection is flexible` than constructor injection.