溫馨提示×
您好，登錄后才能下訂單哦！
點擊 登錄注冊 即表示同意《億速云用戶服務條款》
您好，登錄后才能下訂單哦！
場景復現
你知道MyBatis是怎么實現日志的?額,這個簡單,我知道啊!不就是在mybatis-config.xml文件中配置一下嗎?
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <settings> <setting name="logImpl" value="SLF4J"/> </settings> </configuration>
看,就是上面這么配置就行了,這樣還可以實現日志切換呢!
看官方文檔介紹,有如下日志實現可以切換:
你知道具體的原理嗎?MyBatis是怎樣實現日志切換的呢?
額,這個,這個...(撓頭,源碼還沒看過呢,😓)
源碼擼起來~
對于這個不確定的事,作為程序員的我,怎能輕易說不知道呢?!源碼走起來~
找到一個入口
首先,先從GitHub上將MyBatis的源碼給clone到本地.老大們擼了那么多行代碼,從哪開始下手呢???
大佬們,也是很規范的,寫完代碼有不少的Junit測試類,從test/java中找到了logging包.那就從這開始吧~
@Test
public void shouldReadLogImplFromSettings() throws Exception {
//try-with-resources語句,目的就是為了讀取配置文件IO
//mybatis-config.xml配置文件內容如上,<setting name="logImpl" value="SLF4J"/>
try (Reader reader = Resources.getResourceAsReader("org/apache/ibatis/logging/mybatis-config.xml")) {
//解析配置文件,解析配置文件的代碼就在這了~
new SqlSessionFactoryBuilder().build(reader);
}
Log log = LogFactory.getLog(Object.class);
log.debug("Debug message.");
assertEquals(log.getClass().getName(), NoLoggingImpl.class.getName());
}
SqlSessionFactoryBuilder類
//根據配置文件IO構建SqlSessionFactory
public SqlSessionFactory build(Reader reader) {
return build(reader, null, null);
}
public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
try {
//構建XML配置構建器
XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
//解析XML配置文件
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
reader.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
XMLConfigBuilder XML配置構建器
構造函數
//reader是XML配置文件IO
public XMLConfigBuilder(Reader reader, String environment, Properties props) {
this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
}
//實際調用的XML配置文件構建器構建函數
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
//注意了,這是重點,在這地方調用了父類的構造函數,新建了一個Configuration對象,下面看看Configuration構造函數做了什么
super(new Configuration());
ErrorContext.instance().resource("SQL Mapper Configuration");
this.configuration.setVariables(props);
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
parse解析方法
/**
* 解析 mybatis-config.xml
* @return
*/
public Configuration parse() {
// 只能解析一次
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
//根據XPATH獲取configuration節點
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
parseConfiguration 解析配置方法
private void parseConfiguration(XNode root) {
try {
//issue #117 read properties first
// 解析 properties 節點
propertiesElement(root.evalNode("properties"));
// 解析 settings 節點
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
// 解析 typeAliases 節點
typeAliasesElement(root.evalNode("typeAliases"));
// 解析 plugins 節點
pluginElement(root.evalNode("plugins"));
// 解析 objectFactory 節點
objectFactoryElement(root.evalNode("objectFactory"));
// 解析 objectWrapperFactory 節點
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
// 解析 reflectorFactory 節點
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// 解析 environments 節點， 需要在 objectFactory 和 objectWrapperFactory才能讀取
environmentsElement(root.evalNode("environments"));
// 解析 databaseIdProvider 節點
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
// 解析 typeHandlers 節點
typeHandlerElement(root.evalNode("typeHandlers"));
// 解析 mappers 節點
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
其中Properties settings = settingsAsProperties(root.evalNode("settings"));是解析setttings節點,將settings節點的內容解析到 Properties 對象,其中涉及到很多操作,不在本文分析之列.
settingsElement(settings);將settings中的配置設置到Configuration對象.
settingsElement settings節點的配置
private void settingsElement(Properties props) throws Exception {
...
configuration.setLogPrefix(props.getProperty("logPrefix"));
@SuppressWarnings("unchecked")
// 這個不就是從settings中解析日志的實現嗎?快看看~
// resovleClass是父類BaseBuilder中的方法
Class<? extends Log> logImpl = (Class<? extends Log>) resolveClass(props.getProperty("logImpl"));
//將日志的實現類設置到configuration配置類中
configuration.setLogImpl(logImpl);
configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));
}
Configuration 配置類
public class Configuration {
...
protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
...
public Configuration() {
...
//日志類型別名
typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
languageRegistry.register(RawLanguageDriver.class);
}
}
從上面的Configuration構造函數中可以看到,類型別名中定義了日志實現的名稱與,實現類.class(這些實現類都是MyBatis實現的,稍后再說)
//設置日志實現類
public void setLogImpl(Class<? extends Log> logImpl) {
if (logImpl != null) {
this.logImpl = logImpl;
//調用日志工廠,設置日志實現
LogFactory.useCustomLogging(this.logImpl);
}
}
BaseBuilder
構造函數
public BaseBuilder(Configuration configuration) {
this.configuration = configuration;
//可以看到這個地方的類型別名是從configuration中獲取的
this.typeAliasRegistry = this.configuration.getTypeAliasRegistry();
this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry();
}
protected <T> Class<? extends T> resolveClass(String alias) {
if (alias == null) {
return null;
}
try {
//解析別名
return resolveAlias(alias);
} catch (Exception e) {
throw new BuilderException("Error resolving class. Cause: " + e, e);
}
}
//這個不就是從別名中獲取對應的實現嗎??!
//配置SLF4J,返回Slf4jImpl.class
protected <T> Class<? extends T> resolveAlias(String alias) {
//這個地方的typeAliasRegistry是從configuration中獲取的
return typeAliasRegistry.resolveAlias(alias);
}
TypeAliasRegistry 類型別名
類型別名注冊
//就是將key轉換位小寫,存入HashMap中,key是別名,value是Class類對象
public void registerAlias(String alias, Class<?> value) {
if (alias == null) {
throw new TypeException("The parameter alias cannot be null");
}
// issue #748
String key = alias.toLowerCase(Locale.ENGLISH);
if (TYPE_ALIASES.containsKey(key) && TYPE_ALIASES.get(key) != null && !TYPE_ALIASES.get(key).equals(value)) {
throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + TYPE_ALIASES.get(key).getName() + "'.");
}
TYPE_ALIASES.put(key, value);
}
//根據對應的別名key,獲取實現類class
public <T> Class<T> resolveAlias(String string) {
try {
if (string == null) {
return null;
}
// issue #748
String key = string.toLowerCase(Locale.ENGLISH);
Class<T> value;
if (TYPE_ALIASES.containsKey(key)) {
value = (Class<T>) TYPE_ALIASES.get(key);
} else {
value = (Class<T>) Resources.classForName(string);
}
return value;
} catch (ClassNotFoundException e) {
throw new TypeException("Could not resolve type alias '" + string + "'. Cause: " + e, e);
}
}
Slf4jImpl Slf4j實現類
public class Slf4jImpl implements Log {
private Log log;
public Slf4jImpl(String clazz) {
//使用Slf4j的API獲取日志器
Logger logger = LoggerFactory.getLogger(clazz);
if (logger instanceof LocationAwareLogger) {
try {
// check for slf4j >= 1.6 method signature
logger.getClass().getMethod("log", Marker.class, String.class, int.class, String.class, Object[].class, Throwable.class);
log = new Slf4jLocationAwareLoggerImpl((LocationAwareLogger) logger);
return;
} catch (SecurityException e) {
// fail-back to Slf4jLoggerImpl
} catch (NoSuchMethodException e) {
// fail-back to Slf4jLoggerImpl
}
}
// Logger is not LocationAwareLogger or slf4j version < 1.6
log = new Slf4jLoggerImpl(logger);
}
...
}
可見,最終還是調用具體的日志API實現!
LogFactory 日志工廠
package org.apache.ibatis.logging;
import java.lang.reflect.Constructor;
/**
* 日志工廠
*/
public final class LogFactory {
/**
* Marker to be used by logging implementations that support markers
*/
public static final String MARKER = "MYBATIS";
// 記錄當前使用的第三方日志庫組件所對應的適配器的方法
private static Constructor<? extends Log> logConstructor;
// tryImplementation 進行嘗試加載
static {
tryImplementation(LogFactory::useSlf4jLogging);
tryImplementation(LogFactory::useCommonsLogging);
tryImplementation(LogFactory::useLog4J2Logging);
tryImplementation(LogFactory::useLog4JLogging);
tryImplementation(LogFactory::useJdkLogging);
tryImplementation(LogFactory::useNoLogging);
}
// 私有化
private LogFactory() {
// disable construction
}
public static Log getLog(Class<?> aClass) {
return getLog(aClass.getName());
}
public static Log getLog(String logger) {
try {
return logConstructor.newInstance(logger);
} catch (Throwable t) {
throw new LogException("Error creating logger for logger " + logger + ". Cause: " + t, t);
}
}
/**
* 以下的 useXXXogging 的方法都是嘗試加載日志的實現
* 最終的實現都是 setImplementation
*/
public static synchronized void useCustomLogging(Class<? extends Log> clazz) {
setImplementation(clazz);
}
public static synchronized void useSlf4jLogging() {
setImplementation(org.apache.ibatis.logging.slf4j.Slf4jImpl.class);
}
public static synchronized void useCommonsLogging() {
setImplementation(org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl.class);
}
public static synchronized void useLog4JLogging() {
setImplementation(org.apache.ibatis.logging.log4j.Log4jImpl.class);
}
public static synchronized void useLog4J2Logging() {
setImplementation(org.apache.ibatis.logging.log4j2.Log4j2Impl.class);
}
public static synchronized void useJdkLogging() {
setImplementation(org.apache.ibatis.logging.jdk14.Jdk14LoggingImpl.class);
}
public static synchronized void useStdOutLogging() {
setImplementation(org.apache.ibatis.logging.stdout.StdOutImpl.class);
}
public static synchronized void useNoLogging() {
setImplementation(org.apache.ibatis.logging.nologging.NoLoggingImpl.class);
}
/**
* 嘗試加載
* @param runnable
*/
private static void tryImplementation(Runnable runnable) {
if (logConstructor == null) {
try {
// 會調用 useSlf4jLogging 類似的方法
runnable.run();
} catch (Throwable t) {
// ignore
}
}
}
/**
* 設計日志的實現類
* @param implClass Log 的子類
*/
private static void setImplementation(Class<? extends Log> implClass) {
try {
// 通過反射獲取構造方法
Constructor<? extends Log> candidate = implClass.getConstructor(String.class);
Log log = candidate.newInstance(LogFactory.class.getName());
if (log.isDebugEnabled()) {
log.debug("Logging initialized using '" + implClass + "' adapter.");
}
//設置日志實現的有參構造函數
logConstructor = candidate;
} catch (Throwable t) {
throw new LogException("Error setting Log implementation. Cause: " + t, t);
}
}
}
可以看到其中有靜態代碼塊,隨著類的加載,嘗試加載日志的實現!
總結
通過以上的一步一步分析,可以看到MyBatis是分別通過對日志實現進行進行包裝,最終還是調用具體的日志API實現.
好了，以上就是這篇文章的全部內容了，希望本文的內容對大家的學習或者工作具有一定的參考學習價值，謝謝大家對億速云的支持。
免責聲明：本站發布的內容（圖片、視頻和文字）以原創、轉載和分享為主，文章觀點不代表本網站立場，如果涉及侵權請聯系站長郵箱：is@yisu.com進行舉報，并提供相關證據，一經查實，將立刻刪除涉嫌侵權內容。
