mybatis-spring 自动扫描详解

迈不过友情╰ 2022-05-20 08:52 168阅读 0赞

*  mybatis spring 扫描分析
 *  简介
 *  mapperLocations配置
 *  basePackage通配符配置
    
     *   *  第二版扫描包
 *  总结

# mybatis spring 扫描分析 #

<table> 
 <tbody> 
  <tr> 
   <td>名称</td> 
   <td>版本</td> 
  </tr> 
  <tr> 
   <td>spring</td> 
   <td>5.0.0</td> 
  </tr> 
  <tr> 
   <td>mybatis</td> 
   <td>3.4.6</td> 
  </tr> 
  <tr> 
   <td>mybatis-spring</td> 
   <td>1.3.0</td> 
  </tr> 
 </tbody> 
</table>

# 简介 #

重点内容

这里会有以下几个问题  
1. mapperLocations 明明是一个Resource\[\] ,为什么可以通过`通配符`转换为`Resource[]`  
2. basePackage 怎么做通配符设置

# mapperLocations配置 #

既然要分析如何将`通配符`转换为`Resource[]`,那么不管三七二十一,首先就去 setMapperLocations 下个断点,然后再根据堆栈去回溯

事实上,到这里已经是spring-core的地方了.

![mapperLocattions调用堆栈][mapperLocattions]

在这个栈的代码中,参数是`通配符`,结果是`Resource[]`

protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
            // 删除了所有和主流程无关的代码
            for (PropertyValue pv : original) {
                        convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
                        deepCopy.add(pv);
            }
            bw.setPropertyValues(new MutablePropertyValues(deepCopy));
        }

接下来只要分析 `convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);` 就知道如何转换的了.

然后从 convertForProperty 一层一层的跟进,跟进后,有两个值的注意的代码  
1. findDefaultEditor 查找 `Resource[]` 的属性赋值器 PropertyEditor  
2. doConvertValue 用 PropertyEditor 去设置值

private PropertyEditor findDefaultEditor(@Nullable Class<?> requiredType) {
            // 省略不相关的代码
            return  this.propertyEditorRegistry.getDefaultEditor(requiredType);
        }

private Object doConvertValue(@Nullable Object oldValue, @Nullable Object newValue,
                @Nullable Class<?> requiredType, @Nullable PropertyEditor editor) {
                // 省略不相关的代码
                return doConvertTextValue(oldValue, newTextValue, editor);
        }
    
        private Object doConvertTextValue(@Nullable Object oldValue, String newTextValue, PropertyEditor editor) {
        // 省略不相关的代码
            editor.setAsText(newTextValue);
            return editor.getValue();
        }

那么 propertyEditorRegistry 默认提供了哪些属性赋值器呢? 这里不对属性赋值器进行详解,只是简单的罗列出来

<table> 
 <tbody> 
  <tr> 
   <td>类型</td> 
   <td>属性赋值器</td> 
  </tr> 
  <tr> 
   <td>java.io.InputStream</td> 
   <td>InputStreamEditor</td> 
  </tr> 
  <tr> 
   <td>java.io.Reader</td> 
   <td>ReaderEditor</td> 
  </tr> 
  <tr> 
   <td>java.lang.Class[]</td> 
   <td>ClassArrayEditor</td> 
  </tr> 
  <tr> 
   <td>java.nio.file.Path</td> 
   <td>PathEditor</td> 
  </tr> 
  <tr> 
   <td>org.springframework.core.io.Resource</td> 
   <td>ResourceEditor</td> 
  </tr> 
  <tr> 
   <td>java.lang.Class</td> 
   <td>ClassEditor</td> 
  </tr> 
  <tr> 
   <td>org.xml.sax.InputSource</td> 
   <td>InputSourceEditor</td> 
  </tr> 
  <tr> 
   <td>java.net.URI</td> 
   <td>URIEditor</td> 
  </tr> 
  <tr> 
   <td>java.net.URL</td> 
   <td>URLEditor</td> 
  </tr> 
  <tr> 
   <td>org.springframework.core.io.Resource[]</td> 
   <td>ResourceArrayPropertyEditor</td> 
  </tr> 
  <tr> 
   <td>org.springframework.core.io.ContextResource</td> 
   <td>ResourceEditor</td> 
  </tr> 
 </tbody> 
</table>

那么接下来就去 `Resource[]` 对应的 ResourceArrayPropertyEditor 去分析,是如何进行转换的

public void setAsText(String text) {
            String pattern = resolvePath(text).trim();
            try {
                setValue(this.resourcePatternResolver.getResources(pattern));
            }
            catch (IOException ex) {
                throw new IllegalArgumentException(
                        "Could not resolve resource location pattern [" + pattern + "]: " + ex.getMessage());
            }
        }

跟进 AbstractApplicationContext.getResources 发现关键在于`resourcePatternResolver`

public Resource[] getResources(String locationPattern) throws IOException {
            return this.resourcePatternResolver.getResources(locationPattern);
        }

去寻找 resourcePatternResolver 实际的对象

public AbstractApplicationContext() {
            this.resourcePatternResolver = getResourcePatternResolver();
        }
    
        protected ResourcePatternResolver getResourcePatternResolver() {
                return new PathMatchingResourcePatternResolver(this);
        }

resourcePatternResolver 在构造时,被初始化为:`PathMatchingResourcePatternResolver`

这里不对 PathMatchingResourcePatternResolver 进行深入详解,可以见名知意的理解为: 路径匹配资源的规则解析器

那么也就是说,当函数 setXXX 的参数类型为 Resource\[\] 时,

spring会自动使用ResourceArrayPropertyEditor去赋值,我们就可以直接写通配符

# basePackage通配符配置 #

开发方式从  
\- com.company.mapper/HandlerAMapper  
\- com.company.mapper/HandlerBMapper

转换为  
\- com.company.handlera/mapper/HandlerAMapper  
\- com.company.handlerb/mapper/HandlerAMapper

会有一个好处就是,通模块的Mapper,Service等各种代码都在一起,不用到处找包了.

问题在于 basePackage 它是不支持通配符扫描的,但是支持`,`分割来配置多个包

那么我们要做的就是,将通配符转换为用`,`分割的多个包就行了

接下来用 ScanBasePackage 将`通配符`转换为`用逗号分割的包名`

public class ScanBasePackage { 
        private String wildcard;
    
        public void setWildcard(String wildcard) {
            this.wildcard = wildcard;
        }
    
        public String getPack() throws IOException, ClassNotFoundException {
            ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
            MetadataReaderFactory metadataReaderFactory = new SimpleMetadataReaderFactory(resolver);
            Set<String> stringList = new HashSet<>();
            Resource[] resources = resolver.getResources("classpath*:"+wildcard+".class");
            for(Resource resource:resources){
                MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(resource);
                stringList.add(Class.forName(metadataReader.getClassMetadata().getClassName()).getPackage().getName());
            }
            return stringList.stream().collect(Collectors.joining(","));
        }
    }

然后将xml配置部分的 basePackage 改为 \#\{scanPackageBean.pack\} 占位符的形式

这样就可以不用自己去拼接所有包名了

### 第二版扫描包 ###

那么根据设置setXXX 参数为通配符的理论: 我们把 ScanBasePackage 改成下面这个样子

public class ScanBasePackage { 
        private Resource [] wildcard;
    
        public void setWildcard(Resource [] wildcard) {
            this.wildcard = wildcard;
        }
    
        public String getPack() throws IOException, ClassNotFoundException {
            MetadataReaderFactory metadataReaderFactory = new SimpleMetadataReaderFactory();
            Set<String> stringList = new HashSet<>();
            for(Resource resource:wildcard){
                MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(resource);
                stringList.add(Class.forName(metadataReader.getClassMetadata().getClassName()).getPackage().getName());
            }
            return stringList.stream().collect(Collectors.joining(","));
        }
    }

xml 文件

# 总结 #

1.  使用spring 默认的 PropertyEditor 给mapperLocations 赋值
2.  自定义setXXX 的参数类型为Resource\[\]时,可以使用通配符
3.  使用 PathMatchingResourcePatternResolver 去解析通配符获得包名

[mapperLocattions]: http://cdn.blog.shangwantong.com/mybatis/spring/mapperLocattionsStack.png