真实业务场景
（不希望配置类注册为Bean 或 不希望声明@ConfigurationProperties）
假设某一个jar包内封装了DataSourceProperties
@Configuration
@ConfigurationProperties(
prefix = "my.datasource"
)
@Data
public class DataSourceProperties {
private List<String> suffix;
private List<DataSourceDetailProperties> db;
}
在jar包的Configuration中，某个@Bean的构造过程中引用了这个DataSourceProperties
public JdbcTemplate buildJdbcTemplate(DataSourceProperties dataSourceProperties) {
}
在某个业务场景中，同时存在两个DataSourceProperties 会造成一个问题，注入的时候会提示有多个候选的bean 但是没法去修改Jar包中的内容
自己重复写一个DataSourceProperties 不是很优雅
这时候引出了一个需求，DataSourceProperties不希望注册为Bean，但是能够从配置文件读取构建对象
解决方案一
使用org.springframework.boot.context.properties.bind.Binder 从配置文件构建配置对象
@Bean
public JdbcTemplate buildJdbcTemplate(Environment environment) {
Binder binder = Binder.get(environment);
DataSourceProperties
properties1 = binder.bind("my.datasource1", Bindable.of(DataSourceProperties.class)).get(),
properties2 = binder.bind("my.datasource2", Bindable.of(DataSourceProperties.class)).get();
}
binder.bind("xxx", Bindable.of(type)).get() 似乎是重复的编码方式？
解决方案二
使@Value注解能够支持自动调用这段代码 binder.bind("xxx", Bindable.of(type)).get() 例如
@Bean
public JdbcTemplate buildJdbcTemplate(@Value("my.datasource1") DataSourceProperties properties1,
@Value("my.datasource2") DataSourceProperties properties2) {
}
org.springframework.beans.factory.support.DefaultListableBeanFactory#doResolveDependency 最后会交由converter处理
Class<?> type = descriptor.getDependencyType();
Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if (value != null) {
if (value instanceof String) {
String strVal = resolveEmbeddedValue((String) value);
BeanDefinition bd = (beanName != null && containsBean(beanName) ?
getMergedBeanDefinition(beanName) : null);
value = evaluateBeanDefinitionString(strVal, bd);
}
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
try {
return converter.convertIfNecessary(value, type, descriptor.getTypeDescriptor());
}
catch (UnsupportedOperationException ex) {
// A custom TypeConverter which does not support TypeDescriptor resolution...
return (descriptor.getField() != null ?
converter.convertIfNecessary(value, type, descriptor.getField()) :
converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
}
}
项目启动时，添加String to Object的转换器，支持@Value 并且 "bind:"开头（防止影响@Value原有功能）
package com.nuonuo.accounting.guiding.support.spring;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.context.properties.bind.Bindable;
import org.springframework.boot.context.properties.bind.Binder;
import org.springframework.boot.convert.ApplicationConversionService;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;
import java.util.Set;
import static java.util.Collections.singleton;
public class ValuePropertiesBindableAnnotationSupport implements ApplicationContextInitializer<ConfigurableApplicationContext> {
private static final String PREFIX = "bind:";
@Override
public void initialize(ConfigurableApplicationContext context) {
Binder binder = Binder.get(context.getEnvironment());
((ApplicationConversionService) context.getBeanFactory().getConversionService()).addConverter(new ConditionalGenericConverter() {
@Override
public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
Value value = targetType.getAnnotation(Value.class);
return value != null && value.value().startsWith(PREFIX);
}
@Override
public Set<ConvertiblePair> getConvertibleTypes() {
return singleton(new ConvertiblePair(String.class, Object.class));
}
@Override
public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
Value value = targetType.getAnnotation(Value.class);
Class<?> type = targetType.getType();
assert value != null;
return binder.bind(value.value().replace(PREFIX, ""), Bindable.of(type)).get();
}
});
}
}
转换后代码执行 binder.bind(value.value().replace(PREFIX, ""), Bindable.of(type)).get(); 目的就达成了
在META-INF/spring.factories中添加注册的Bean
# ApplicationContextInitializer
org.springframework.context.ApplicationContextInitializer=\
com.nuonuo.accounting.guiding.support.spring.ValuePropertiesBindableAnnotationSupport,\
最终效果
@Bean
public JdbcTemplate buildJdbcTemplate(@Value("bind:my.datasource1") DataSourceProperties properties1,
@Value("bind:my.datasource2") DataSourceProperties properties2) {
}以上就是Value注解支持对象类型ConfigurationProperties功能的详细内容，更多关于Value支持对象类型的资料请关注编程网其它相关文章！
