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Spring-19 Auto-Wiring by type
在Xml文件中定义bean之间的关系时，有3种方法：
1. inner bean
2. 在bean 的property中定义另外一个bean
3. Spring Autowiring（有很多种类型， 这里 by type）
<bean id="logger" class="com.caveofprogramming.spring.test.Logger" autowire="byType"> </bean> <bean id="consolewriter" class="com.caveofprogramming.spring.test.ConsoleWriter"> </bean> <bean id="filewriter" class="com.caveofprogramming.spring.test.FileWriter"> </bean>
Auto-wiring 的两个问题：
1. When project is very big, it hard to know what exactly happen when use Auto-wiring.
2. beans which are wired should exactly matched. It will exist error casue of ambiguity. For example:
<bean id="logger" class="com.caveofprogramming.spring.test.Logger" autowire="byType"> </bean> <bean id="consolewriter" class="com.caveofprogramming.spring.test.ConsoleWriter"> </bean> <bean id="consolewriter1" class="com.caveofprogramming.spring.test.ConsoleWriter"> </bean>
<bean id="filewriter" class="com.caveofprogramming.spring.test.FileWriter"> </bean> </beans>
Interface 的 Implement 也可能出现 ambiguity的问题。
package com.caveofprogramming.spring.test; public class Logger { private ConsoleWriter consoleWriter; private FileWriter fileWriter; public void setConsoleWriter(ConsoleWriter consoleWriter) { this.consoleWriter = consoleWriter; } public void setFileWriter(FileWriter fileWriter) { this.fileWriter = fileWriter; } public void writeFile(String text){ fileWriter.write(text); } public void writeConsole(String text){ consoleWriter.write(text); } }
Spring-20 Autowiring by Name
（注意 logger.class与 Spring-19 中的区别 ambiguity）
package com.caveofprogramming.spring.test; public class Logger { private LogWriter consoleWriter; private LogWriter fileWriter; public void setConsoleWriter(LogWriter writer) { this.consoleWriter = writer; } public void setFileWriter(LogWriter fileWriter) { this.fileWriter = fileWriter; } public void writeFile(String text){ fileWriter.write(text); } public void writeConsole(String text){ consoleWriter.write(text); } }
<bean id="logger" class="com.caveofprogramming.spring.test.Logger" autowire="byName"> </bean> <bean id="consoleWriter" class="com.caveofprogramming.spring.test.ConsoleWriter"> </bean> <bean id="fileWriter" class="com.caveofprogramming.spring.test.FileWriter"> </bean>
而且，variables 和 bean中的 id 要 match。
Spring-21 Autowiring by Constructor
package com.caveofprogramming.spring.test; public class Logger { private LogWriter consoleWriter; private LogWriter fileWriter; public Logger(ConsoleWriter consoleWriter, FileWriter fileWriter){ this.consoleWriter = consoleWriter; this.fileWriter = fileWriter; } public void setConsoleWriter(LogWriter writer) { this.consoleWriter = writer; } public void setFileWriter(LogWriter fileWriter) { this.fileWriter = fileWriter; } public void writeFile(String text){ fileWriter.write(text); } public void writeConsole(String text){ consoleWriter.write(text); } }
<bean id="logger" class="com.caveofprogramming.spring.test.Logger" autowire="constructor"> </bean> <bean id="consoleWriter" class="com.caveofprogramming.spring.test.ConsoleWriter"> </bean> <bean id="fileWriter" class="com.caveofprogramming.spring.test.FileWriter"> </bean>
Constructor 是通过Type来match的？？
用了autowire=“constructor”后，不能再property？？
Spring-22 Default Autowiring
解决Defalult Autowiring 中的byType中的ambiguity
package com.caveofprogramming.spring.test; public class Logger { private ConsoleWriter consoleWriter; private FileWriter fileWriter; /* public Logger(ConsoleWriter consoleWriter, FileWriter fileWriter){ this.consoleWriter = consoleWriter; this.fileWriter = fileWriter; */ public void setConsoleWriter(ConsoleWriter writer) { this.consoleWriter = writer; } public void setFileWriter(FileWriter fileWriter) { this.fileWriter = fileWriter; } public void writeFile(String text){ fileWriter.write(text); } public void writeConsole(String text){ consoleWriter.write(text); } }
<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.xsd" default-autowire="byType" default-autowire-candidates="consoleWriter,fileWriter"> <bean id="logger" class="com.caveofprogramming.spring.test.Logger"> </bean> <bean id="consoleWriter" class="com.caveofprogramming.spring.test.ConsoleWriter"> </bean> <bean id="fileWriter" class="com.caveofprogramming.spring.test.FileWriter"> </bean> <bean id="fileWriter1" class="com.caveofprogramming.spring.test.FileWriter"> </bean> </beans>
Spring-22 Removing Autowire Ambiguities
1. autowire-cadidate="false"
2. primary = "true"
<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.xsd" default-autowire="byType" > <bean id="logger" class="com.caveofprogramming.spring.test.Logger"> </bean> <bean id="consoleWriter" class="com.caveofprogramming.spring.test.ConsoleWriter"> </bean> <bean id="fileWriter" class="com.caveofprogramming.spring.test.FileWriter"> </bean> <bean id="fileWriter1" class="com.caveofprogramming.spring.test.FileWriter" autowire-candidate="false"> </bean>
<bean id="logger" class="com.caveofprogramming.spring.test.Logger"> </bean> <bean id="consoleWriter" class="com.caveofprogramming.spring.test.ConsoleWriter" primary="true"> </bean> <bean id="consoleWriter1" class="com.caveofprogramming.spring.test.ConsoleWriter"> </bean> <bean id="fileWriter" class="com.caveofprogramming.spring.test.FileWriter"> </bean> <bean id="fileWriter1" class="com.caveofprogramming.spring.test.FileWriter" autowire-candidate="false"> </bean>
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原文地址：http://www.cnblogs.com/patrickspring/p/4912924.html
