On the way learning spring 4-白红宇

On the way learning spring 4

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发布时间：2019-06-28

本文共 3646 字，大约阅读时间需要 12 分钟。

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）

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:

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);    }    }

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);    }    }

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);    }    }