裝配Spring Bean

目標(biāo)：

掌握3種依賴注入的方式
掌握如何使用XML裝配Bean
掌握如何使用注解方式裝配Bean及消除歧義
掌握如何使用profile 和條件裝配Bean
掌握Bean 的作用域
了解Spring EL的簡(jiǎn)易使用

依賴注入的3種方式：

構(gòu)造器注入
setter注入
接口注入

構(gòu)造器注入:

構(gòu)造器注入依賴于構(gòu)造方法實(shí)現(xiàn)，而構(gòu)造方法可以是有參數(shù)或是無(wú)參數(shù)的，在大部分的情況下，我們都是通過(guò)類的構(gòu)造器方法來(lái)創(chuàng)建類的對(duì)象，Spring也可以采用反射的方式，通過(guò)構(gòu)造方法來(lái)完成注入，這就是構(gòu)造器注入的原理。

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n26" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.ssm.chapter9.pojo;

public class Role {
private Long id;
private String roleName;
private String note;

public Role(String roleName, String note) {
this.roleName = roleName;
this.note = note;
}

public Long getId() {
return id;
}

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

public String getRoleName() {
return roleName;
}

public void setRoleName(String roleName) {
this.roleName = roleName;
}

public String getNote() {
return note;
}

public void setNote(String note) {
this.note = note;
}

}
</pre>

constructor-arg元素用于定義類構(gòu)造方法的參數(shù)，其中index用于定義參數(shù)的位置，而value則是設(shè)置值。

這個(gè)注入比較簡(jiǎn)單，但無(wú)法應(yīng)用大量參數(shù)的程式

使用setter注入:

setter注入是Spring中最主流注入方式，它利用Java Bean規(guī)范所定義的setter方法來(lái)完成注入，靈活且可讀性高。

首先把構(gòu)造方法聲明為無(wú)參數(shù)的，然后使用setter注入為其設(shè)置對(duì)應(yīng)的值，其實(shí)是通過(guò)Java反射技術(shù)得以實(shí)現(xiàn)。

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n33" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.ssm.chapter9.pojo;

public class Role {
private Long id;
private String roleName;
private String note;

public Role() {

}
public Role(String roleName, String note) {
this.roleName = roleName;
this.note = note;
}

public Long getId() {
return id;
}

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

public String getRoleName() {
return roleName;
}

public void setRoleName(String roleName) {
this.roleName = roleName;
}

public String getNote() {
return note;
}

public void setNote(String note) {
this.note = note;
}

}</pre>

這樣Spring就會(huì)通過(guò)反射調(diào)用沒(méi)有參數(shù)的構(gòu)造方法生成對(duì)象，同時(shí)通過(guò)反射對(duì)應(yīng)的setter注入配置的值了，這種方式是Spring最主要的方式。

接口注入：

接口注入主要來(lái)自外界

裝配Bean概述

Spring 中提供3中方法進(jìn)行配置：

在xml中顯示配置。
在Java的接口和類中實(shí)現(xiàn)配置。
隱式配置的接口發(fā)現(xiàn)機(jī)制和自動(dòng)裝配原則

3種方式優(yōu)先級(jí)：

基于約定優(yōu)于配置的原則，最優(yōu)先的應(yīng)該是通過(guò)隱式Bean的發(fā)現(xiàn)機(jī)制和自動(dòng)裝配的原則.這樣的好處是減少程序開發(fā)者的決定權(quán)，簡(jiǎn)單又不失靈活。
在沒(méi)有辦法使用自動(dòng)裝配原則的情況下應(yīng)該優(yōu)先考慮Java接口和類中實(shí)現(xiàn)配置，這樣的好處是避免xml配置的泛濫，也更為容易。這種場(chǎng)景典型的例子是一個(gè)父類有多個(gè)子類，比如學(xué)生類有兩個(gè)子類:男生類和女生類，通過(guò)IoC容器初始化一個(gè)學(xué)生類，容器將無(wú)法知道使用哪個(gè)子類去初始化，這個(gè)時(shí)候可以使用Java的注解配置去指定。
在上述方法無(wú)法使用的情況下，那么只能選擇xml去配置Spring IoC容器。由于現(xiàn)實(shí)工作中常常用到第三方的類庫(kù)，有些類并不是我們開發(fā)的，我們無(wú)法修改里面的代碼，這個(gè)時(shí)候就通過(guò)xml的方式配置使用了。

通過(guò)XML配置配置裝配Bean：

xml對(duì)于剛接觸Spring IoC容器的人來(lái)說(shuō)更為清晰明了，使用xml裝配Bean需要定義對(duì)應(yīng)的Spring Bean的元素。

裝配簡(jiǎn)易值

id="role2" id屬性是spring找到的一個(gè)Bean的編號(hào)，不過(guò)id不是一個(gè)必須的屬性，如果沒(méi)有聲明它，那么Spring將會(huì)采用“全限定名#{number}”的格式編號(hào)。com.ssm.chapter9.pojo.Role#0==bean id="role2" class="com.ssm.chapter9.pojo.Role"
class顯然是一個(gè)類的全限定名
property元素是定義類的屬性，其中name屬性定義的是屬性的名稱，而value是其值。

裝配集合：

有些時(shí)候要一些復(fù)雜的裝配工作，比如Set，Map，List，Array，Properties等。先定義Bean

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n71" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.ssm.chapter10.pojo;

import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;

public class ComplexAssembly {

private Long id;
private List<String> list;
private Map<String, String> map;
private Properties props;
private Set<String> set;
private String[] array;

public Long getId() {
return id;
}

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

public List<String> getList() {
return list;
}

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

public Map<String, String> getMap() {
return map;
}

public void setMap(Map<String, String> map) {
this.map = map;
}

public Properties getProps() {
return props;
}

public void setProps(Properties props) {
this.props = props;
}

public Set<String> getSet() {
return set;
}

public void setSet(Set<String> set) {
this.set = set;
}

public String[] getArray() {
return array;
}

public void setArray(String[] array) {
this.array = array;
}

}</pre>

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="xml" cid="n72" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;"><bean id="complexAssembly" class="com.ssm.chapter10.pojo.ComplexAssembly">
<property name="id" value="1" />
<property name="list">
<list>
<value>value-list-1</value>
<value>value-list-2</value>
<value>value-list-3</value>
</list>
</property>
<property name="map">
<map>
<entry key="key1" value="value-key-1" />
<entry key="key2" value="value-key-2" />
<entry key="key3" value="value-key-3" />
</map>
</property>
<property name="props">
<props>
<prop key="prop1">value-prop-1</prop>
<prop key="prop2">value-prop-2</prop>
<prop key="prop3">value-prop-3</prop>
</props>
</property>
<property name="set">
<set>
<value>value-set-1</value>
<value>value-set-2</value>
<value>value-set-3</value>
</set>
</property>
<property name="array">
<array>
<value>value-array-1</value>
<value>value-array-2</value>
<value>value-array-3</value>
</array>
</property>
</bean></pre>

List屬性為對(duì)應(yīng)的<list>元素進(jìn)行裝配，然后通過(guò)多個(gè)<value>元素設(shè)值。
Map屬性為對(duì)應(yīng)的<map>元素進(jìn)行裝配，然后通過(guò)多個(gè)<entry>元素設(shè)值，只是entry包含一個(gè)鍵（key）和一個(gè)值（value）的設(shè)值。
Properties屬性，為對(duì)應(yīng)的<Properties>元素進(jìn)行裝配，然后通過(guò)多個(gè)<Property>元素設(shè)值,只是property元素有一個(gè)必填屬性key，然后可以設(shè)值。
Set屬性為對(duì)應(yīng)的<set>元素進(jìn)行裝配，然后通過(guò)多個(gè)<value>元素設(shè)值.
對(duì)于數(shù)組而言，<array>元素進(jìn)行裝配，然后通過(guò)多個(gè)<value>元素設(shè)值.

從上面看到對(duì)字符串的各個(gè)集合加載，但是有些時(shí)候可能需要更為復(fù)雜的裝載，比如一個(gè)List可以是一個(gè)系列類的對(duì)象，又如一個(gè)Map集合類，鍵可以是一個(gè)類的對(duì)象，而值也要是一個(gè)類的對(duì)象。

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n85" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.ssm.chapter10.pojo;

public class Role {
private Long id;
private String roleName;
private String note;

public Role() {
}

public Role(Long id, String roleName, String note) {
this.id = id;
this.roleName = roleName;
this.note = note;
}

public Long getId() {
return id;
}

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

public String getRoleName() {
return roleName;
}

public void setRoleName(String roleName) {
this.roleName = roleName;
}

public String getNote() {
return note;
}

public void setNote(String note) {
this.note = note;
}

}
</pre>

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n86" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.ssm.chapter10.pojo;

public class User {
private Long id;
private String userName;
private String note;

public Long getId() {
return id;
}

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

public String getUserName() {
return userName;
}

public void setUserName(String userName) {
this.userName = userName;
}

public String getNote() {
return note;
}

public void setNote(String note) {
this.note = note;
}

}
</pre>

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n87" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.ssm.chapter10.pojo;

import java.util.List;
import java.util.Map;
import java.util.Set;

public class UserRoleAssembly {

private Long id;
private List<Role> list;
private Map<Role, User> map;
private Set<Role> set;

public Long getId() {
return id;
}

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

public List<Role> getList() {
return list;
}

public void setList(List<Role> list) {
this.list = list;
}

public Map<Role, User> getMap() {
return map;
}

public void setMap(Map<Role, User> map) {
this.map = map;
}

public Set<Role> getSet() {
return set;
}

public void setSet(Set<Role> set) {
this.set = set;
}

}
</pre>

這里定義了兩個(gè)角色Bean（role1和role2）和兩個(gè)用戶Bean（user1和user2），他們和之前定義沒(méi)有什么不同，只是后面的定義略微不同而已。

List屬性為對(duì)應(yīng)的<list>元素定義注入，然后使用多個(gè)<ref>元素的Bean屬性去引用之前定義好的Bean。
Map屬性使用<map>元素定義注入，然后使用多個(gè)<entry>元素的key-ref屬性去引用之前定義好的Bean作為鍵，而用value-ref屬性去引用之前定義好的Bean作為值。
Set屬性使用<set>元素定義注入，然后使用多個(gè)<ref>元素的Bean屬性去引用之前定義好的Bean

命名空間裝配：

Spring還提供對(duì)應(yīng)的命名空間的定義，只是在使用命名空間的時(shí)候要先引入對(duì)應(yīng)的命名空間和xml模式。

<util:list id="list">
<ref bean="role1" />
<ref bean="role2" />
</util:list>

<util:map id="map">
<entry key-ref="role1" value-ref="user1" />
<entry key-ref="role2" value-ref="user2" />
</util:map>

<util:set id="set">
<ref bean="role1" />
<ref bean="role2" />
</util:set>

xmlns:c="http://www.springframework.org/schema/c"

xmlns:p="http://www.springframework.org/schema/p"

xmlns:util="http://www.springframework.org/schema/util"

注意加粗的代碼，它們定義了XML的命名空間，這樣才能在內(nèi)容里面使用p和c這樣的前綴定義
id為role1的角色定義，c:0代表構(gòu)造方法的第一個(gè)參數(shù)，c:1代表的是第2個(gè)，c:_2代表的是第3個(gè)，以此類推。
id為role2的角色定義，p代表引用屬性，其中p：id=“2”以2為值，使用setId方法設(shè)置，roleName，note屬性也是一樣的道理

通過(guò)注解裝配Bean：

從上面的例子已知如何使用XML的方式去裝配Bean，但更多的時(shí)候已經(jīng)不推薦使用XMl的方式去裝配Bean，更多時(shí)候回考慮使用注解（annotation）的方式去裝配Bean，使用注解方式可以減少xml的配置，注解功能更為強(qiáng)大，它既能實(shí)現(xiàn)XML的功能，也提供了自動(dòng)裝配的功能，采用了自動(dòng)裝配后，程序員所需要做的決斷就少了，更有利對(duì)程序的開發(fā)，這就是“約定優(yōu)于配置”的開發(fā)原則。

在Spring中，它提供了兩種方式來(lái)讓Spring IoC容器發(fā)現(xiàn)Bean。

組件掃描：通過(guò)定義資源的方式，讓Spring IoC容器掃描對(duì)應(yīng)的包，從而把Bean裝配進(jìn)來(lái)。
自動(dòng)裝配：通過(guò)注解定義，使得一些依賴關(guān)系可以通過(guò)注解完成。

通過(guò)掃描和自動(dòng)裝配，大部分的工程都可以用Java配置完成，而不是xml，可以有效減少配置和引入大量xml。

如果系統(tǒng)存在多個(gè)公共的配置文件（多個(gè)properties和xml文件）或第三方資源，使用xml配置會(huì)更加明確。

以注解為主，以xml配置為輔。

使用@Component裝配Bean

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n123" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.pojo;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component(value = "role")
public class Role {
@Value("1")
private Long id;
@Value("role_name_1")
private String roleName;
@Value("role_note_1")
private String note;

public Long getId() {
return id;
}

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

public String getRoleName() {
return roleName;
}

public void setRoleName(String roleName) {
this.roleName = roleName;
}

public String getNote() {
return note;
}

public void setNote(String note) {
this.note = note;
}

}
</pre>

注意註解@Component(value = "role")，@Value("1")

註解@Component代表Spring IoC會(huì)把這個(gè)類掃描生成Bean實(shí)例，而其中的value屬性代表在Spring中的id，這就相當(dāng)于XML方式定義的Bean的id，（<bean id="role_1"class="com.ssm.chapter9.pojo.Role">也可以簡(jiǎn)寫成@Component("role")，甚至直接寫成@Componen，對(duì)于不寫的，Spring IoC容器就默認(rèn)類名，但是以首字母小寫的形式作為id，為其生成對(duì)象，配置到容器中。
注解@Value代表的是值得注入，這里只是簡(jiǎn)單注入一些值，其中id是一個(gè)long型，注入的時(shí)候Spring會(huì)為其轉(zhuǎn)換類型。

Spring IoC掃描類：

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n131" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.pojo;

import org.springframework.context.annotation.ComponentScan;

@ComponentScan
public class PojoConfig {

}
</pre>

注意:package com.zw.pojo; @ComponentScan

包名和代碼清單需要一致（package com.zw.pojo;）
@ComponentScan代表進(jìn)行掃描，默認(rèn)是掃描當(dāng)前包的路徑，POJO的包名和它保持一致才能掃描，否則沒(méi)有的。

測(cè)試：

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n139" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.main;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.zw.pojo.PojoConfig;
import com.zw.pojo.Role;

public class Demo1Main {

public static void main(String[] args) {
// TODO Auto-generated method stub
ApplicationContext context = new AnnotationConfigApplicationContext(PojoConfig.class);
Role role=context.getBean(Role.class);
System.out.println(role.getId());
}

}
</pre>

此處有兩個(gè)明顯的弊端：

對(duì)于@ComponentScan注解，它只掃描所在包的Java類，但是更多的時(shí)候真正需要的是可以掃描所指定的類
上面只是注入了一些簡(jiǎn)單的值，而沒(méi)有注入對(duì)象，同樣在現(xiàn)實(shí)的開發(fā)可以注入對(duì)象是十分重要的

@ComponentScan有兩個(gè)配置項(xiàng)：

basePackages：base Packages Package+s Package表示包，s表示多個(gè)包。
basePackageClasses：base Package Classes Class+es Class表示類，es表示多個(gè)類。

驗(yàn)證@ComponentScan的兩個(gè)配置項(xiàng)，首先定義一個(gè)接口RoleService：

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n153" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.service;

import com.zw.pojo.Role;

public interface RoleService {
public void printRoleInfo(Role role);

}
</pre>

使用接口編寫一些操作類是Spring所推薦的，它可以將定義和實(shí)現(xiàn)分離，這樣就更為靈活。

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n155" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.service.impl;

import org.springframework.stereotype.Component;

import com.sun.org.apache.xerces.internal.impl.dv.dtd.IDDatatypeValidator;
import com.zw.pojo.Role;
import com.zw.service.RoleService;
@Component
public class RoleServiceImpl implements RoleService {

@Override
public void printRoleInfo(Role role) {
// TODO Auto-generated method stub
System.out.println("id="+role.getId());
System.out.println("roleName="+role.getRoleName());
System.out.println("note="+role.getNote());
}

}
</pre>

這里的@ComponentScan表明它是一個(gè)Spring所需要的Bean。而且也實(shí)現(xiàn)了對(duì)應(yīng)的RoleService接口所定義的printRoleInfo方法，

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n158" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.config;

import static org.springframework.test.web.client.match.MockRestRequestMatchers.content;

import org.springframework.context.annotation.ComponentScan;

import com.zw.pojo.Role;
import com.zw.service.impl.RoleServiceImpl;

@ComponentScan(basePackageClasses= {Role.class,RoleServiceImpl.class})//重構(gòu)項(xiàng)目使用它，便于報(bào)錯(cuò)讀取
//@ComponentScan(basePackages= {"com.zw.pojo.Role","com.zw.service"}) //項(xiàng)目?jī)?yōu)先使用它，可讀性比較好

public class ApplicationConfig {

}
</pre>

注意：

這是對(duì)掃描包的定義，可以采用任意一個(gè)@ComponentScan去定義，也可以取消代碼中的注釋。
如果采用多個(gè)@ComponentScan去定義對(duì)應(yīng)的包，但是每定義一個(gè)@ComponentScan，Spring就會(huì)產(chǎn)生一個(gè)新的對(duì)象，也就是所配置的Bean將會(huì)生成多個(gè)實(shí)例，這往往不是我們所需要的。
對(duì)于已定義的basePackages和basePackageClasses的@ComponentScan，Spring會(huì)進(jìn)行專門的區(qū)分，也就是說(shuō)在同一個(gè)@ComponentScan中即使重復(fù)定義相同的包或者存在其子包的定義，也不會(huì)造成因一個(gè)Bean的多次掃描，而導(dǎo)致一次配置生成多個(gè)對(duì)象。

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n167" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.main;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.zw.config.ApplicationConfig;
import com.zw.pojo.PojoConfig;
import com.zw.pojo.Role;
import com.zw.service.RoleService;
import com.zw.service.impl.RoleServiceImpl;

public class Demo1Main {

public static void main(String[] args) {
// TODO Auto-generated method stub
test2();
}

private static void test1() {
ApplicationContext context = new AnnotationConfigApplicationContext(PojoConfig.class);
Role role=context.getBean(Role.class);
System.out.println(role.getId());
}
private static void test2() {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ApplicationConfig.class);
Role role=context.getBean(Role.class);
RoleService roleService=context.getBean(RoleService.class);
roleService.printRoleInfo(role);
context.close();

}

}
</pre>

自動(dòng)裝配--@Autowired:

前面提到兩個(gè)問(wèn)題之一就是沒(méi)有注入對(duì)象，關(guān)于這個(gè)問(wèn)題，在注解中略微有點(diǎn)復(fù)雜。大部分的情況下建議使用自動(dòng)裝配，因?yàn)榭梢詼p少配置的復(fù)雜度。前面的Spring學(xué)習(xí)，Spring是先完成Bean的定義和生成，然后尋找需要注入的資源。

<pre mdtype="fences" cid="n170" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.service;

public interface RoleService2 {
public void printRoleInfo();

}
</pre>

Spring 推薦的接口方式，這個(gè)更靈活。因?yàn)閷⒍x和實(shí)現(xiàn)分離了。

<pre mdtype="fences" cid="n174" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.service.impl;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.zw.pojo.Role;
import com.zw.service.RoleService2;
@Component("RoleService2")

public class RoleServiceImpl2 implements RoleService2 {
@Autowired
private Role role=null;

public Role getRole() {
return role;
}

public void setRole(Role role) {
this.role = role;
}

@Override
public void printRoleInfo() {
// TODO Auto-generated method stub
System.out.println("id="+role.getId());
System.out.println("roleName="+role.getRoleName());
System.out.println("note="+role.getNote());
}

}
</pre>

@Autowired

private Role role=null;

@Autowired注解，表示在Spring IoC定位所有的Bean后，這個(gè)字段需要按類型注入，這樣IoC容器就會(huì)尋找資源，然后將其注入。

<pre mdtype="fences" cid="n176" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.main;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.zw.config.ApplicationConfig;
import com.zw.pojo.PojoConfig;
import com.zw.pojo.Role;
import com.zw.service.RoleService;
import com.zw.service.RoleService2;
import com.zw.service.impl.RoleServiceImpl;

public class Demo1Main {

public static void main(String[] args) {
// TODO Auto-generated method stub
test3();
}

}

private static void test3() {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ApplicationConfig.class);
RoleService2 roleService = context.getBean(RoleService2.class);
roleService.printRoleInfo();
context.close();

}

}
</pre>

自動(dòng)裝配的歧視性（@Primary和@Qualifier）：

@Autowired在一個(gè)接口有多個(gè)實(shí)現(xiàn)類的時(shí)候無(wú)法使用

<pre mdtype="fences" cid="n194" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.service.impl;

import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;

import com.zw.pojo.Role;
import com.zw.service.RoleService;
@Component("roleService3")
//@Primary //測(cè)試@Primary 一個(gè)接口存在多個(gè)實(shí)現(xiàn)類區(qū)分優(yōu)先處理
public class RoleServiceImpl3 implements RoleService{

@Override
public void printRoleInfo(Role role) {
// TODO Auto-generated method stub
System.out.println("id ="+role.getId());
System.out.println(",roleName ="+role.getRoleName());
System.out.println("roleService3note ="+role.getNote());
}

}
</pre>

在新建一個(gè)RoleController類，它有個(gè)字段RoleService類型。

<pre mdtype="fences" cid="n201" lang="java" class="md-fences md-end-block ty-contain-cm modeLoaded md-focus" spellcheck="false" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package com.zw.controlller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.zw.pojo.Role;
import com.zw.service.RoleService;
@Component
//Controlller 控制器
public class RoleControlller {
@Autowired
private RoleService roleService=null;
public void printRole(Role role) {
roleService.printRoleInfo(role);

}

}
</pre>

這里的字段 RoleService是一個(gè)RoleService接口類型。RoleService有兩個(gè)實(shí)現(xiàn)類。分別是RoleServiceImpl和RoleServiceImpl3，這個(gè)時(shí)候Spring IoC容器就會(huì)犯糊涂，無(wú)法判斷把那個(gè)對(duì)象注入進(jìn)來(lái)，于是就會(huì)拋出異常。這樣@Autowired就失敗了。

//@Primary //測(cè)試@Primary 一個(gè)接口存在多個(gè)實(shí)現(xiàn)類區(qū)分優(yōu)先處理

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# 裝配Spring Bean