MyBatis中怎么實現(xiàn)一個日志模塊

這期內容當中小編將會給大家?guī)碛嘘PMyBatis中怎么實現(xiàn)一個日志模塊，文章內容豐富且以專業(yè)的角度為大家分析和敘述，閱讀完這篇文章希望大家可以有所收獲。

SqlSessionFactoryBuilder類

//根據(jù)配置文件IO構建SqlSessionFactorypublic 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(shù)

//reader是XML配置文件IOpublic 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(shù)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(shù),新建了一個Configuration對象,下面看看Configuration構造函數(shù)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(jù)XPATH獲取configuration節(jié)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(jié)點    propertiesElement(root.evalNode("properties"));    // 解析 settings 節(jié)點    Properties settings = settingsAsProperties(root.evalNode("settings"));    loadCustomVfs(settings);    // 解析 typeAliases 節(jié)點    typeAliasesElement(root.evalNode("typeAliases"));    // 解析 plugins 節(jié)點    pluginElement(root.evalNode("plugins"));    // 解析 objectFactory 節(jié)點    objectFactoryElement(root.evalNode("objectFactory"));    // 解析 objectWrapperFactory 節(jié)點    objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));    // 解析 reflectorFactory 節(jié)點    reflectorFactoryElement(root.evalNode("reflectorFactory"));    settingsElement(settings);    // 解析 environments 節(jié)點， 需要在 objectFactory 和 objectWrapperFactory才能讀取    environmentsElement(root.evalNode("environments"));    // 解析 databaseIdProvider 節(jié)點    databaseIdProviderElement(root.evalNode("databaseIdProvider"));    // 解析 typeHandlers 節(jié)點    typeHandlerElement(root.evalNode("typeHandlers"));    // 解析 mappers 節(jié)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(jié)點,將settings節(jié)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(jié)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(xiàn)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(xiàn)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(shù)中可以看到,類型別名中定義了日志實現(xiàn)的名稱與,實現(xiàn)類.class(這些實現(xiàn)類都是MyBatis實現(xiàn)的,稍后再說)

//設置日志實現(xiàn)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(xiàn)    LogFactory.useCustomLogging(this.logImpl);  }}

BaseBuilder

構造函數(shù)

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(xiàn)嗎??!//配置SLF4J,返回Slf4jImpl.classprotected <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(jù)對應的別名key,獲取實現(xiàn)類classpublic <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(xiàn)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(xiàn)!

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(xiàn)  * 最終的實現(xiàn)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(xiàn)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(xiàn)的有參構造函數(shù)   logConstructor = candidate;  } catch (Throwable t) {   throw new LogException("Error setting Log implementation. Cause: " + t, t);  } }}

上述就是小編為大家分享的MyBatis中怎么實現(xiàn)一個日志模塊了，如果剛好有類似的疑惑，不妨參照上述分析進行理解。如果想知道更多相關知識，歡迎關注億速云行業(yè)資訊頻道。