Spring源码-入门
一、测试类
public class Main {
public static void main(String[] args) {
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:app-${user}.xml");
Person person = applicationContext.getBean(Person.class);
System.out.println(person.getName());
}
}
同时添加jvm参数-Duser=test
二、app-test.xml文件
<beans>
<bean id="person" class="xml.Person">
<property value="张三" name="name"></property>
</bean>
</beans>
三、源码跟踪
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
创建ClassPathXmlApplicationContext从xml位置加载Bean定义。
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
super(parent); // 初始化父类
setConfigLocations(configLocations); // 设置xml文件位置
if (refresh) {
refresh(); // 刷新容器
}
}
从super(parent);进去
public AbstractApplicationContext(@Nullable ApplicationContext parent) {
this();
setParent(parent);
}
@Override
public void setParent(@Nullable ApplicationContext parent) {
this.parent = parent;
if (parent != null) {
Environment parentEnvironment = parent.getEnvironment();
if (parentEnvironment instanceof ConfigurableEnvironment) {
getEnvironment().merge((ConfigurableEnvironment) parentEnvironment); // 与父类的Environment对象合并
}
}
}
public void setConfigLocations(@Nullable String... locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
this.configLocations[i] = resolvePath(locations[i]).trim(); // 解析xml文件的路径，xml文件路径可能存在${}的情况，需要解析替换
}
}
else {
this.configLocations = null;
}
}
protected String resolvePath(String path) {
return getEnvironment().resolveRequiredPlaceholders(path); // 解析${...}并替换
}
@Override
public ConfigurableEnvironment getEnvironment() {
if (this.environment == null) {
this.environment = createEnvironment();
}
return this.environment;
}
protected ConfigurableEnvironment createEnvironment() {
return new StandardEnvironment();
}
查看StandardEnvironment的父类AbstractEnvironment构造函数
public AbstractEnvironment() {
this(new MutablePropertySources());
}
protected AbstractEnvironment(MutablePropertySources propertySources) {
this.propertySources = propertySources;
this.propertyResolver = createPropertyResolver(propertySources);
customizePropertySources(propertySources);
}
protected void customizePropertySources(MutablePropertySources propertySources) {
}
StandardEnvironment的customizePropertySources方法
@Override
protected void customizePropertySources(MutablePropertySources propertySources) {
propertySources.addLast(
new PropertiesPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
propertySources.addLast(
new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
}
AbstractEnvironment类
@Override
@SuppressWarnings({"rawtypes", "unchecked"})
public Map<String, Object> getSystemProperties() {
try {
return (Map) System.getProperties(); // 获取JVM属性
}
catch (AccessControlException ex) {
return (Map) new ReadOnlySystemAttributesMap() {
@Override
@Nullable
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;
}
}
};
}
}
@Override
@SuppressWarnings({"rawtypes", "unchecked"})
public Map<String, Object> getSystemEnvironment() {
if (suppressGetenvAccess()) {
return Collections.emptyMap();
}
try {
return (Map) System.getenv(); // 获取系统设置的属性
}
catch (AccessControlException ex) {
return (Map) new ReadOnlySystemAttributesMap() {
@Override
@Nullable
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;
}
}
};
}
}
resolveRequiredPlaceholders
//AbstractEnvironment
@Override
public String resolveRequiredPlaceholders(String text) throws IllegalArgumentException {
return this.propertyResolver.resolveRequiredPlaceholders(text); \\ propertyResolver是PropertySourcesPropertyResolver
}
在创建StandardEnvironment对象时
public AbstractEnvironment() {
this(new MutablePropertySources());
}
protected AbstractEnvironment(MutablePropertySources propertySources) {
this.propertySources = propertySources;
this.propertyResolver = createPropertyResolver(propertySources);
customizePropertySources(propertySources);
}
protected ConfigurablePropertyResolver createPropertyResolver(MutablePropertySources propertySources) {
return new PropertySourcesPropertyResolver(propertySources);
}
PropertySourcesPropertyResolver的父类AbstractPropertyResolver的方法resolveRequiredPlaceholders
@Override
public String resolveRequiredPlaceholders(String text) throws IllegalArgumentException {
if (this.strictHelper == null) {
this.strictHelper = createPlaceholderHelper(false);
}
return doResolvePlaceholders(text, this.strictHelper);
}
private String doResolvePlaceholders(String text, PropertyPlaceholderHelper helper) {
return helper.replacePlaceholders(text, this::getPropertyAsRawString);
}
public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
Assert.notNull(value, "'value' must not be null");
return parseStringValue(value, placeholderResolver, null);
}
protected String parseStringValue(
String value, PlaceholderResolver placeholderResolver, @Nullable Set<String> visitedPlaceholders) {
int startIndex = value.indexOf(this.placeholderPrefix); //placeholderPrefix = "${"; 查找前缀位置
if (startIndex == -1) {
return value;
}
StringBuilder result = new StringBuilder(value);
while (startIndex != -1) {
int endIndex = findPlaceholderEndIndex(result, startIndex); // 从startIndex开始在result查找placeholderSuffix的位置
if (endIndex != -1) {
String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
String originalPlaceholder = placeholder;
if (visitedPlaceholders == null) {
visitedPlaceholders = new HashSet<>(4);
}
if (!visitedPlaceholders.add(originalPlaceholder)) {
throw new IllegalArgumentException(
"Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
}
// Recursive invocation, parsing placeholders contained in the placeholder key.
placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders); //递归调用parseStringValue解析placeholder，${}里面可能存在${}
// Now obtain the value for the fully resolved key...
String propVal = placeholderResolver.resolvePlaceholder(placeholder); //通过系统属性解析placeholder
if (propVal == null && this.valueSeparator != null) { // 设置默认值
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);
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();
}
private int findPlaceholderEndIndex(CharSequence buf, int startIndex) {
int index = startIndex + this.placeholderPrefix.length();
int withinNestedPlaceholder = 0;
while (index < buf.length()) {
if (StringUtils.substringMatch(buf, index, this.placeholderSuffix)) { // placeholderSuffix = "}"
if (withinNestedPlaceholder > 0) {
withinNestedPlaceholder--;
index = index + this.placeholderSuffix.length();
}
else {
return index;
}
}
else if (StringUtils.substringMatch(buf, index, this.simplePrefix)) {
withinNestedPlaceholder++;
index = index + this.simplePrefix.length();
}
else {
index++;
}
}
return -1;
}
