上一篇文章说完了自定义配置文件properties的写法，并且介绍了采用classpath*通配模式下读取多个同名文件的内容方法。
下面就要进入到对springboot的默认配置文件application.properties的分析了。
二、springboot读取默认配置文件深入探究
1.springboot启动用运行
通过run里面跟踪下去，会执行到ConfigurableApplicationContext run(String... args)里面，在里面初始化sprignboot的上下文配置。它的listern（ConfigFileApplicationListener）会对它的执行进行监听。
ConfigFileApplicationListener里面存在一些static变量，我们先来看一下他们,后面都会用到。
注意下面的 DEFAULT_SEARCH_LOCATIONS ，都是采用classpath:的模式，并没有带*
public class ConfigFileApplicationListener
implements EnvironmentPostProcessor, SmartApplicationListener, Ordered {
private static final String DEFAULT_PROPERTIES = "defaultProperties";
// Note the order is from least to most specific (last one wins)
private static final String DEFAULT_SEARCH_LOCATIONS = "classpath:/,classpath:/config/,file:./,file:./config/";
private static final String DEFAULT_NAMES = "application";
...
/**
* The "config location" property name.
*/
public static final String CONFIG_LOCATION_PROPERTY = "spring.config.location";
/**
* The "config additional location" property name.
*/
public static final String CONFIG_ADDITIONAL_LOCATION_PROPERTY = "spring.config.additional-location";
...
}
调用到ConfigFileApplicationListener 里面的
addLoadedPropertySources(ConfigurableEnvironment environment,ResourceLoader resourceLoader)，该方法内部会初始化Loader对象，调用load()函数。
下面进入正文——我们来详细看一下load()函数
public void load() {
this.profiles = new LinkedList<>();
this.processedProfiles = new LinkedList<>();
this.activatedProfiles = false;
this.loaded = new LinkedHashMap<>();
initializeProfiles();
while (!this.profiles.isEmpty()) {
Profile profile = this.profiles.poll();
if (profile != null && !profile.isDefaultProfile()) {
addProfileToEnvironment(profile.getName());
}
load(profile, this::getPositiveProfileFilter,
addToLoaded(MutablePropertySources::addLast, false));
this.processedProfiles.add(profile);
}
load(null, this::getNegativeProfileFilter,
addToLoaded(MutablePropertySources::addFirst, true));
addLoadedPropertySources();
}
可以发现里面profiles.poll()一开始为空，所以会调用
load(profile, this::getPositiveProfileFilter,
addToLoaded(MutablePropertySources::addLast, false));
2.真正读取的地方
首先来看一下load源码
private void load(Profile profile, DocumentFilterFactory filterFactory,
DocumentConsumer consumer) {
getSearchLocations().forEach((location) -> {
boolean isFolder = location.endsWith("/");
Set<String> names = isFolder ? getSearchNames() : NO_SEARCH_NAMES;
names.forEach(
(name) -> load(location, name, profile, filterFactory, consumer));
});
}
3. 先调用getSearchLocations()方法
接着相应的搜索地方调用查找位置，除非配置了spring.config.location
private Set<String> getSearchLocations() {
if (this.environment.containsProperty(CONFIG_LOCATION_PROPERTY)) {
return getSearchLocations(CONFIG_LOCATION_PROPERTY);
}
Set<String> locations = getSearchLocations(
CONFIG_ADDITIONAL_LOCATION_PROPERTY);
locations.addAll(
asResolvedSet(ConfigFileApplicationListener.this.searchLocations,
DEFAULT_SEARCH_LOCATIONS));
return locations;
}
3.1继续进入其中的asResolvedSet()方法
这里面做了一个reverse操作
private Set<String> asResolvedSet(String value, String fallback) {
List<String> list = Arrays.asList(StringUtils.trimArrayElements(
StringUtils.commaDelimitedListToStringArray((value != null)
? this.environment.resolvePlaceholders(value) : fallback)));
Collections.reverse(list);
return new LinkedHashSet<>(list);
}
4. 接着我们来看 getSearchNames()方法
操作都差不多，大同小异，先看下有没有设置别名，没有的话就采用默认的application名称
private Set<String> getSearchNames() {
if (this.environment.containsProperty(CONFIG_NAME_PROPERTY)) {
String property = this.environment.getProperty(CONFIG_NAME_PROPERTY);
return asResolvedSet(property, null);
}
return asResolvedSet(ConfigFileApplicationListener.this.names, DEFAULT_NAMES);
}
5. 最后我们来看一下foreach里面的load方法
如果找得到name(即上面默认情况下的application，或者自定义名称)的情况下，就进行相应的配置文件的读取
private void load(String location, String name, Profile profile,
DocumentFilterFactory filterFactory, DocumentConsumer consumer) {
if (!StringUtils.hasText(name)) {
for (PropertySourceLoader loader : this.propertySourceLoaders) {
if (canLoadFileExtension(loader, location)) {
load(loader, location, profile,
filterFactory.getDocumentFilter(profile), consumer);
return;
}
}
}
Set<String> processed = new HashSet<>();
for (PropertySourceLoader loader : this.propertySourceLoaders) {
for (String fileExtension : loader.getFileExtensions()) {
if (processed.add(fileExtension)) {
loadForFileExtension(loader, location + name, "." + fileExtension,
profile, filterFactory, consumer);
}
}
}
}
5.1 继续进入第一个if的load()方法
别看这段代码长，实际上就是try里面的第一句有用，后面都是一些情况判断
private void load(PropertySourceLoader loader, String location, Profile profile,
DocumentFilter filter, DocumentConsumer consumer) {
try {
Resource resource = this.resourceLoader.getResource(location);
if (resource == null || !resource.exists()) {
if (this.logger.isTraceEnabled()) {
this.logger.trace("Skipped missing config "
+ getDescription(location, resource, profile));
}
return;
}
if (!StringUtils.hasText(
StringUtils.getFilenameExtension(resource.getFilename()))) {
if (this.logger.isTraceEnabled()) {
this.logger.trace("Skipped empty config extension "
+ getDescription(location, resource, profile));
}
return;
}
String name = "applicationConfig: [" + location + "]";
List<Document> documents = loadDocuments(loader, name, resource);
if (CollectionUtils.isEmpty(documents)) {
if (this.logger.isTraceEnabled()) {
this.logger.trace("Skipped unloaded config "
+ getDescription(location, resource, profile));
}
return;
}
List<Document> loaded = new ArrayList<>();
for (Document document : documents) {
if (filter.match(document)) {
addActiveProfiles(document.getActiveProfiles());
addIncludedProfiles(document.getIncludeProfiles());
loaded.add(document);
}
}
Collections.reverse(loaded);
if (!loaded.isEmpty()) {
loaded.forEach((document) -> consumer.accept(profile, document));
if (this.logger.isDebugEnabled()) {
this.logger.debug("Loaded config file "
+ getDescription(location, resource, profile));
}
}
}
catch (Exception ex) {
throw new IllegalStateException("Failed to load property "
+ "source from location '" + location + "'", ex);
}
}
5.2 与自定义配置文件相连
自此，就和前面的给串联起来了。getResource因为不是classpath*模式，所以会走到上面代码的最后一个else
// a single resource with the given name
return new Resource[] {getResourceLoader().getResource(locationPattern)};
而getResourceLoader().getResource(locationPattern)最后返回的是一个Resource对象，所以对于Resource[]中只会有一个对象存在。
5.3我们在进一步查看它的实现类
public interface ResourceLoader {
/** Pseudo URL prefix for loading from the class path: "classpath:" */
String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;
/**
* Return a Resource handle for the specified resource location.
* <p>The handle should always be a reusable resource descriptor,
* allowing for multiple {@link Resource#getInputStream()} calls.
* <p><ul>
* <li>Must support fully qualified URLs, e.g. "file:C:/test.dat".
* <li>Must support classpath pseudo-URLs, e.g. "classpath:test.dat".
* <li>Should support relative file paths, e.g. "WEB-INF/test.dat".
* (This will be implementation-specific, typically provided by an
* ApplicationContext implementation.)
* </ul>
* <p>Note that a Resource handle does not imply an existing resource;
* you need to invoke {@link Resource#exists} to check for existence.
* @param location the resource location
* @return a corresponding Resource handle (never {@code null})
* @see #CLASSPATH_URL_PREFIX
* @see Resource#exists()
* @see Resource#getInputStream()
*/
Resource getResource(String location);
进一步看它的实现类，如果是for循环里面找到一个值，就会返回
@Override
public Resource getResource(String location) {
Assert.notNull(location, "Location must not be null");
for (ProtocolResolver protocolResolver : this.protocolResolvers) {
Resource resource = protocolResolver.resolve(location, this);
if (resource != null) {
return resource;
}
}
if (location.startsWith("/")) {
return getResourceByPath(location);
}
else if (location.startsWith(CLASSPATH_URL_PREFIX)) {
return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
}
else {
try {
// Try to parse the location as a URL...
URL url = new URL(location);
return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
}
catch (MalformedURLException ex) {
// No URL -> resolve as resource path.
return getResourceByPath(location);
}
}
}
public ClassPathResource(String path, @Nullable ClassLoader classLoader) {
Assert.notNull(path, "Path must not be null");
String pathToUse = StringUtils.cleanPath(path);
if (pathToUse.startsWith("/")) {
pathToUse = pathToUse.substring(1);
}
this.path = pathToUse;
this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
}
6. 当读取完后会回到 1 下面的执行最后的加载参数
addLoadedPropertySources();
总结:对于classpath模式会全局查找多处结果合并，而classpath只要找到一个就停止了。所以采用默认模块下面的配置文件，application.properties，在单项目多模块下，记得要在web模块（即启动模块）下放置一个就好了。这样一方面便于管理，一方面也不会出现重复覆盖的问题。
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