spring learning code 1

Thu, Apr 16, 2020 6-minute read

This is my learning note about how Spring core features like IoC, AOP works, with Code Examples .

Spring Code Learning Notes with Code Examples

Spring Code Learning Notes with Code Examples

spring introduce

download

inport jar

Beans
Core
Context
Expression

create class and mothod


public class User {
    public void add() {
        System.out.println("add.............");
    }
}

create an object with Spring properties

1. xml file in Spring properties

test

1. load spring properties file

2. get object from properties (bean id)

Spring IOC

1. spring ioc basic concepts

xml encoding, factory-based design pattern, reflect
original: tightly coupled

class UserService{
    execute();
    UserDao dao = new UserDao();
    dao.add();
}

class UserDao{
    add() {
        ...
    }
}

factory-based design pattern

class UserService{
    execute();
    UserDao dao = UserFactory.getDao();
    dao.add();
}

class UserDao{
    add() {
        ...
    }
}

class UserFactory{
    public static UserDao getDao() {
        return new UserDao();
    }
}

IOC

<bean id="user" class="com.learn.User"></bean>

class UserFactory{
    public static UserDao getDao() {
        // 1. xml encoding
        String classValue = class属性;
        // 2. use reflect create an object
        Class clazz = Class.for(Name);
        return (UserDao)clazz.newInstance();
    }
}

2. IOC interface(BeanFactory)

BeanFactory: for String, not for developer
- won’t creates object when loading properties file
ApplicationContext
- creating objects when loading properties file

3. IOC opertation Bean management(xml)

creating objects in xml(bean)

bean tag properties
- id, class…
- create objects by No-argument constructor
set properties in xml
- DI: set properties
DI: set method

1). create class, and set method

public void setBname(String bname) {
    this.bname = bname;
}

2). spring xml file, set properties

DI: use annotation

1). create class, and set method, and argument constructor

public class Orders{
    private String oname;
    private String address;

    public Order(String oname, String address) {
        this.oname = oname;
        this.address = address;
    }
}

2). spring xml file, use argument constructor

4. Bean management(xml) external beans

2 classes: service and dao
call methods in dao from service class

// service and dao objects: 在service层创建UserDAO类，生成set方法
<bean id="userService" class="com.learn.service.UserService">
// inject userDao object
// name attribute: class attribute name private UserDao userDao;
<property name="userDao" ref="userDaoImpl"></property>
</bean>
<bean id="userDaoImpl" class="com.learn.dao.UserDaoImpl"></bean>

5. Bean management(xml) inner beans and Cascade assignment

1 对多关系：部门和员工
在实体类之间表示 1 对多关系

department

public class Dept {
    private String dname;
    public void setDname(String dname) {
        this.dname = dname;
    }
}

employ

public class Emp {
    private String ename;
    private Dept dept;
    public void setDept(Dept dept) {
        this.dept = dept;
    }
}

xml

// inner bean
<bean id="emp" class="com.learn.bean.Emp">
// inject userDao object
<property name="ename" value="lucy"></property>
// method 1
// <property name="dept" ref="dame"></property>
// method 2
<property name="dept">
    <bean id="dept" class="com.learn.bean.Dept">
    <property name="dname" value="IT"></property>
</property>
</bean>

6. Bean management(xml) array, list, map

6.1 class and set method

public class Stu {
    // array
    private String[] courses;
    // list
    private List<String> list;

    // map
    private Map<String, String> maps;

    // set
    private Set<String> sets;

    public void setCourses(String[] courses) {
        this.courses = courses;
    }
      
    public void setList( List<String> list) {
        this.list =  list;
    }
    public void setMap(Map<String, String> maps) {
        this.maps =  maps;
    }
    public void setSet(Set<String> sets) {
        this.sets =  sets;
    }
}

6.2 xml


<bean id="stu" class="com.learn.conllectiontype.Stu">

// array
<property name="courses">
    <array>
        <value>java class </value>
        <value>sql class </value>
    </array>
</property>

// list
<property name="list">
    <list>
        <value>AAA </value>
        <value>BBB class </value>
    </list>
</property>

// MAP
<property name="maps">
    <map>
        <entry>key="JAVA" value="jva"</entry>
        <entry>key="PHP" value="php"</entry>
    </map>
</property>

// set
<property name="sets">
    <set>
       <value>MySQL </value>
        <value>Redis </value>
    </set>
</property>
</bean>

7. Bean managementset object type in collection

7.1 class and set method

public class Course {
    private String cname;
    public void setCname(String cname) {
        this.cname = cname;
    }

    public String toString() {

    }

}

public class Stu {
    // array
    private String[] courses;
    // list
    private List<String> list;

    // map
    private Map<String, String> maps;

    // set
    private Set<String> sets;

    // ===============coursed students take===============
    private List<Course> courseList;

    public void setCourseList(List<Course> courseList) {
        this.courseList = courseList;
    }
    // ===============coursed students take===============

    public void setCourses(String[] courses) {
        this.courses = courses;
    }
      
    public void setList( List<String> list) {
        this.list =  list;
    }
    public void setMap(Map<String, String> maps) {
        this.maps =  maps;
    }
    public void setSet(Set<String> sets) {
        this.sets =  sets;
    }
}

7.2 xml


<bean id="stu" class="com.learn.conllectiontype.Stu">

// array
<property name="courses">
    <array>
        <value>java class </value>
        <value>sql class </value>
    </array>
</property>

// list
<property name="list">
    <list>
        <value>AAA </value>
        <value>BBB class </value>
    </list>
</property>

// MAP
<property name="maps">
    <map>
        <entry>key="JAVA" value="jva"</entry>
        <entry>key="PHP" value="php"</entry>
    </map>
</property>

// set
<property name="sets">
    <set>
       <value>MySQL </value>
        <value>Redis </value>
    </set>
</property>
</bean>

// ===============inject list collection type, value is object===============
<property name="courseList">
    <list>
       <ref bean="course1"></ref>
       <ref bean="course2"></ref>
    </list>
</property>
// ===============create multiple course objects===============
<bean id="course1" class="com.learn.collectiontype.Course">
    <property name="cname" value="Spring5"></property>
</bean>
<bean id="course2" class="com.learn.collectiontype.Course">
    <property name="cname" value="MyBatis"></property>
</bean>

8. extract injection in collection

8.1 Book class

public class Book {
    private List<String> list;
    public void setList(List<String> list) {
        this.list = list;
    }

    public String toString() {
        
    }

    public void test() {
        System.out.println(list);
    }

}

8.2 in xml import name space util

<bean xmlns=""
      xmlns:p=""
    //   copy xmlns:p
      xmlns:util="http://www.springframework.org/schema/util"

    //   change xsi:schemaLocation beans to util
    //   xsi:schemaLocation="http://www.springframework.org/schema/beans" "http://www.springframework.org/schema/beans/spring-beans.xsd"
      xsi:schemaLocation="http://www.springframework.org/schema/util" "http://www.springframework.org/schema/util/spring-util.xsd">

8.3 util tag

// 1. list=====================
<util:list id="bookList">
        <value>AAA </value>
        <value>BBB</value>
        <value>CCC</value>
</util:list>

8.4 test

@Test
public void testCollection() {
    ApplicationContext context = new ClassPathXmlApplicationContext("bean2.xml");
Book book = context.getBean("book", Book.class);
book.test();
}

9. IOC manage Bean (factory beans)

9.1 ordinary beans 定义 bean 类型就是返回类型

9.2 factory beans 配置文件定义 bean 类型和返回类型不一样

9.2.1 创建类，作为工厂 bean，实现接口 FactoryBean
9.2.2 实现接口里面的方法，在方法中定义返回的 bean 类型

10. Spring Bean Scopes

10.1 single or instances will be created 单实例多实例 10.2 default model is single instance 默认 spring bean 是单实例对象 10.3 scope is used to set single or multiple: singleton or protype 10.4 singleton vs protype

singleton: create instance when load spring xml file
prototype: create instances when getBean method