日期： 2019-03-21
编写spring启动入口：
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ClassPathXmlApplicationContext构造器的类加载逻辑：使用给定父级创建新的ClassPathXmlApplicationContext， 从给定的XML文件加载定义的类。
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这篇文章主要讲解：super(parent) 和 setConfigLocations(configLocations) 逻辑。
1 . supper（parent）的逻辑：调用到父类
org.springframework.context.support.AbstractApplicationContext() 构造器。
/**
*@see org.springframework.context.support.AbstractApplicationContext#setParent(ApplicationContext)
*/
public AbstractApplicationContext(ApplicationContext parent) {
//对用户设置的配置文件位置处理，主要是通配符（${ }）的处理
this();
//设置父类容器,合并环境变量。主要是系统变量和jvm变量
setParent(parent);
}
设置父类容器，合并环境变量：在spring作为父容器时，springmvc将spring父容器引用过来，可以获取到spring容器的参数和配置，但是父容器不能访问子容器的配置，原因就在于此。
public void setParent(ApplicationContext parent) {
this.parent = parent;
if (parent != null) {
Environment parentEnvironment = parent.getEnvironment();
if (parentEnvironment instanceof ConfigurableEnvironment) {
getEnvironment().merge((ConfigurableEnvironment) parentEnvironment);
}
}
}
接下看看环境变量到底是做什么的：parent.getEnvironment();
public ConfigurableEnvironment getEnvironment() {
if (this.environment == null) {
this.environment = createEnvironment();
}
return this.environment;
}
protected ConfigurableEnvironment createEnvironment() {
return new StandardEnvironment();
}
public class StandardEnvironment extends AbstractEnvironment {
/** System environment property source name: {@value} */
public static final String SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME = "systemEnvironment";
/** JVM system properties property source name: {@value} */
public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";
/**
* 将系统参数变量和jvm参数变量加入缓存map缓存
* Customize the set of property sources with those appropriate for any standard
* Java environment:
* <ul>
* <li>{@value #SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME}
* <li>{@value #SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME}
* </ul>
* <p>Properties present in {@value #SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME} will
* take precedence over those in {@value #SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME}.
* @see AbstractEnvironment#customizePropertySources(MutablePropertySources)
* @see #getSystemProperties()
* @see #getSystemEnvironment()
*/
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {
propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
}
}
//获取系统参数变量
public Map<String, Object> getSystemEnvironment() {
if (suppressGetenvAccess()) {
return Collections.emptyMap();
}
try {
return (Map) System.getenv();
}
catch (AccessControlException ex) {
return (Map) new ReadOnlySystemAttributesMap() {
@Override
protected String getSystemAttribute(String attributeName) {
try {
return System.getenv(attributeName);
}
catch (AccessControlException ex) {
if (logger.isInfoEnabled()) {
logger.info("Caught AccessControlException when accessing system environment variable '" +
attributeName + "'; its value will be returned [null]. Reason: " + ex.getMessage());
}
return null;
}
}
};
}
}
//获取jvm参数变量
@SuppressWarnings({"unchecked", "rawtypes"})
public Map<String, Object> getSystemProperties() {
try {
return (Map) System.getProperties();
}
catch (AccessControlException ex) {
return (Map) new ReadOnlySystemAttributesMap() {
@Override
protected String getSystemAttribute(String attributeName) {
try {
return System.getProperty(attributeName);
}
catch (AccessControlException ex) {
if (logger.isInfoEnabled()) {
logger.info("Caught AccessControlException when accessing system property '" +
attributeName + "'; its value will be returned [null]. Reason: " + ex.getMessage());
}
return null;
}
}
};
}
}
最后，merge方法融合父类容器配置：getEnvironment().merge((ConfigurableEnvironment) parentEnvironment)：
@Override
public void merge(ConfigurableEnvironment parent) {
for (PropertySource<?> ps : parent.getPropertySources()) {
if (!this.propertySources.contains(ps.getName())) {
this.propertySources.addLast(ps);
}
}
/**
获取明确配置的profile（key="spring.profiles.active"，默认为key="spring.profiles.default")
eg 通过配置jvm参数方式设置：-Dspring.profiles.active=dev
通过web.xml方式来设置：
<context-param>
<param-name>spring.profiles.active</param-name>
<param-value>dev</param-value>
</context-param>
*/
String[] parentActiveProfiles = parent.getActiveProfiles();
if (!ObjectUtils.isEmpty(parentActiveProfiles)) {
synchronized (this.activeProfiles) {
for (String profile : parentActiveProfiles) {
this.activeProfiles.add(profile);
}
}
}
String[] parentDefaultProfiles = parent.getDefaultProfiles();
if (!ObjectUtils.isEmpty(parentDefaultProfiles)) {
synchronized (this.defaultProfiles) {
this.defaultProfiles.remove(RESERVED_DEFAULT_PROFILE_NAME);
for (String profile : parentDefaultProfiles) {
this.defaultProfiles.add(profile);
}
}
}
}
2 . setConfigLocations（String[]）处理配置文件位置
/**
* Set the config locations for this application context.
* <p>If not set, the implementation may use a default as appropriate.
* 对配置的配置文件的位置进行通配符的处理，然后，保存在configLocations数组中
*/
public void setConfigLocations(String... locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
//对配置文件路径的${}转义，分隔符为“：”
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
resolvePath（String）方法最后会调用到PropertyPlaceholderHelper#parseStringValue（String , PlaceholderResolver , Set<String>）方法：
1）查找${key}通配符，找到其中key对应value
2）递归查找${key}，替换为value。
3）如果value为null，则查找分隔符":"的位置，截取分割符后面的值作为value
protected String parseStringValue(
String value, PlaceholderResolver placeholderResolver, Set<String> visitedPlaceholders) {
StringBuilder result = new StringBuilder(value);
//查找 “${” 的位置
int startIndex = value.indexOf(this.placeholderPrefix);
while (startIndex != -1) {
// 查找最后一个 “}” 的位置
int endIndex = findPlaceholderEndIndex(result, startIndex);
if (endIndex != -1) {
String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
String originalPlaceholder = placeholder;
if (!visitedPlaceholders.add(originalPlaceholder)) {
throw new IllegalArgumentException(
"Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
}
// Recursive invocation, parsing placeholders contained in the placeholder key.
//递归获取${}中的值
placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
// Now obtain the value for the fully resolved key...
String propVal = placeholderResolver.resolvePlaceholder(placeholder);
if (propVal == null && this.valueSeparator != null) {
// propVal 为null时，查找分隔符“：”后面的值作为value
int separatorIndex = placeholder.indexOf(this.valueSeparator);
if (separatorIndex != -1) {
String actualPlaceholder = placeholder.substring(0, separatorIndex);
String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
if (propVal == null) {
propVal = defaultValue;
}
}
}
if (propVal != null) {
// Recursive invocation, parsing placeholders contained in the
// previously resolved placeholder value.
propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
//将${}获取的value，替换原来的${}
result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
if (logger.isTraceEnabled()) {
logger.trace("Resolved placeholder '" + placeholder + "'");
}
startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length());
}
else if (this.ignoreUnresolvablePlaceholders) {
// Proceed with unprocessed value.
startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
}
else {
throw new IllegalArgumentException("Could not resolve placeholder '" +
placeholder + "'" + " in value \"" + value + "\"");
}
visitedPlaceholders.remove(originalPlaceholder);
}
else {
startIndex = -1;
}
}
return result.toString();
}
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