寫在前面
這個demo來說明怎么一步步排查一個常見的spring boot AutoConfiguration的錯誤。
https://github.com/hengyunabc/spring-boot-inside/tree/master/demo-database-type-NONE
調試排查 Cannot determine embedded database driver class for database type NONE 的錯誤
把工程導入IDE里，直接啟動應用，拋出來的異常信息是：
Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2017-11-29 14:26:34.478 ERROR 29736 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter :
***************************
APPLICATION FAILED TO START
***************************
Description:
Cannot determine embedded database driver class for database type NONE
Action:
If you want an embedded database please put a supported one on the classpath. If you have database settings to be loaded from a particular profile you may need to active it (no profiles are currently active).
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其實這時有兩個思路，直接google搜索Cannot determine embedded database driver class for database type NONE，就可以找到解決辦法。
第二種方式，仔細查看日志內容，可以發現有To display the auto-configuration report re-run your application with 'debug' enabled.。
搜索下這個，就可以在spring的官方網站上找到相關的信息：https://docs.spring.io/spring-boot/docs/current/reference/html/using-boot-auto-configuration.html
就是用戶只要配置了debug這個開關，就會把auto-configuration 相關的信息打印出來。
熟悉spring的環境變量注入的話，就可以知道有幾種打開這個的方式：
在args里增加--debug
在application.properties里增加debug=true
通過-Ddebug=true
增加debug開關之后的信息
增加debug開關之后，可以看到打印出了錯誤堆棧：
2017-11-29 14:33:08.776 DEBUG 29907 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter : Application failed to start due to an exception
org.springframework.boot.autoconfigure.jdbc.DataSourceProperties$DataSourceBeanCreationException: Cannot determine embedded database driver class for database type NONE. If you want an embedded database please put a supported one on the classpath. If you have database settings to be loaded from a particular profile you may need to active it (no profiles are currently active).
at org.springframework.boot.autoconfigure.jdbc.DataSourceProperties.determineDriverClassName(DataSourceProperties.java:245) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
at org.springframework.boot.autoconfigure.jdbc.DataSourceProperties.initializeDataSourceBuilder(DataSourceProperties.java:182) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
at org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration.createDataSource(DataSourceConfiguration.java:42) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
at org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration$Tomcat.dataSource(DataSourceConfiguration.java:53) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_112]
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拋出異常的代碼是：
/**
* Determine the driver to use based on this configuration and the environment.
* @return the driver to use
* @since 1.4.0
*/
public String determineDriverClassName() {
if (StringUtils.hasText(this.driverClassName)) {
Assert.state(driverClassIsLoadable(),
"Cannot load driver class: " + this.driverClassName);
return this.driverClassName;
}
String driverClassName = null;
if (StringUtils.hasText(this.url)) {
driverClassName = DatabaseDriver.fromJdbcUrl(this.url).getDriverClassName();
}
if (!StringUtils.hasText(driverClassName)) {
driverClassName = this.embeddedDatabaseConnection.getDriverClassName();
}
if (!StringUtils.hasText(driverClassName)) {
throw new DataSourceBeanCreationException(this.embeddedDatabaseConnection,
this.environment, "driver class");
}
return driverClassName;
}
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可以看出來是沒有找到 DataSource 的driver class，然后拋出了 DataSourceBeanCreationException。
那么一種解決辦法是，在maven依賴里加入一些 DataSource driver class。
但是應用自己的代碼里並沒有使用DataSource，哪里導致spring boot要創建一個DataSource對象？
哪里導致spring boot要創建DataSource
從異常棧上，可以找到DataSourceConfiguration$Tomcat 這個類，那么查找下它的引用，可以發現它是被org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration.PooledDataSourceConfiguration import引入的。
@Configuration
@Conditional(PooledDataSourceCondition.class)
@ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
@Import({ DataSourceConfiguration.Tomcat.class, DataSourceConfiguration.Hikari.class,
DataSourceConfiguration.Dbcp.class, DataSourceConfiguration.Dbcp2.class,
DataSourceConfiguration.Generic.class })
protected static class PooledDataSourceConfiguration {
}
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那么 PooledDataSourceConfiguration 是怎么生效的呢？從代碼上可以看到@Conditional(PooledDataSourceCondition.class)。
那么再看PooledDataSourceCondition的具體實現：
/**
* {@link AnyNestedCondition} that checks that either {@code spring.datasource.type}
* is set or {@link PooledDataSourceAvailableCondition} applies.
*/
static class PooledDataSourceCondition extends AnyNestedCondition {
PooledDataSourceCondition() {
super(ConfigurationPhase.PARSE_CONFIGURATION);
}
@ConditionalOnProperty(prefix = "spring.datasource", name = "type")
static class ExplicitType {
}
@Conditional(PooledDataSourceAvailableCondition.class)
static class PooledDataSourceAvailable {
}
}
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PooledDataSourceCondition引入了@Conditional(PooledDataSourceAvailableCondition.class) ：
/**
* {@link Condition} to test if a supported connection pool is available.
*/
static class PooledDataSourceAvailableCondition extends SpringBootCondition {
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context,
AnnotatedTypeMetadata metadata) {
ConditionMessage.Builder message = ConditionMessage
.forCondition("PooledDataSource");
if (getDataSourceClassLoader(context) != null) {
return ConditionOutcome
.match(message.foundExactly("supported DataSource"));
}
return ConditionOutcome
.noMatch(message.didNotFind("supported DataSource").atAll());
}
/**
* Returns the class loader for the {@link DataSource} class. Used to ensure that
* the driver class can actually be loaded by the data source.
* @param context the condition context
* @return the class loader
*/
private ClassLoader getDataSourceClassLoader(ConditionContext context) {
Class<?> dataSourceClass = new DataSourceBuilder(context.getClassLoader())
.findType();
return (dataSourceClass == null ? null : dataSourceClass.getClassLoader());
}
}
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從代碼里，可以看到是嘗試查找dataSourceClass，如果找到，條件就成立。那么debug下，可以發現查找到的dataSourceClass是：org.apache.tomcat.jdbc.pool.DataSource 。
那么再看下org.apache.tomcat.jdbc.pool.DataSource這個類是從哪里來的呢？
從maven依賴樹可以看到，依賴是來自：spring-boot-starter-jdbc。所以是應用依賴了spring-boot-starter-jdbc，但是並沒有配置DataSource引起的問題。
問題解決辦法
有兩種：
沒有使用到DataSource，則可以把spring-boot-starter-jdbc的依賴去掉，這樣就不會觸發spring boot相關的代碼
把spring boot自動初始化DataSource相關的代碼禁止掉
禁止的辦法有兩種：
在main函數上配置exclude
@SpringBootApplication(exclude = { DataSourceAutoConfiguration.class, DataSourceTransactionManagerAutoConfiguration.class })
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在application.properties里配置：
spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration
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總結
應用沒有使用到DataSource，但是在pom.xml里引入了spring-boot-starter-jdbc
spring-boot-starter-jdbc帶入了tomcat-jdbc，它里面有org.apache.tomcat.jdbc.pool.DataSource
spring boot里的PooledDataSourceConfiguration，判斷classpath下面有DataSource的實現類，嘗試去創建DataSource bean
在初始化DataSourceProperties時，嘗試通過jdbc的url來探測driver class
因為應用並沒有配置url，所以最終在DataSourceProperties.determineDriverClassName()里拋出Cannot determine embedded database driver class for database type NONE
最后：
排查spring boot的AutoConfiguration問題時，可以按異常棧，一層層排查Configuration是怎么引入的，再排查Condition具體的判斷代碼。
原文鏈接：https://blog.csdn.net/hengyunabc/article/details/78762097