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一 点睛
通过分析依赖关系,可知spring-boot-starter-data-jpa依赖于spring-boot-starter-jdbc,所以有必要先研究一下Spring Boot对JDBC的支持。
Spring Boot对JDBC做了一些自动配置,源码位置如下:
二 源码分析
1 DataSourceProperties类分析
@ConfigurationProperties(prefix = DataSourceProperties.PREFIX)
public class DataSourceProperties
implements BeanClassLoaderAware, EnvironmentAware, InitializingBean {
public static final String PREFIX = "spring.datasource"; //该前缀的属性自动配置DataSource
......
}
2 DataSourceTransactionManagerAutoConfiguration类分析
@Configuration
@ConditionalOnClass({ JdbcTemplate.class, PlatformTransactionManager.class })
@AutoConfigureOrder(Ordered.LOWEST_PRECEDENCE)
public class DataSourceTransactionManagerAutoConfiguration {
@Autowired(required = false)
private DataSource dataSource;
@Bean
@ConditionalOnMissingBean(PlatformTransactionManager.class)
@ConditionalOnBean(DataSource.class)
public DataSourceTransactionManager transactionManager() {
return new DataSourceTransactionManager(this.dataSource);
}
@ConditionalOnMissingBean(AbstractTransactionManagementConfiguration.class)
@Configuration
//自动开启了注解事务的支持
@EnableTransactionManagement
protected static class TransactionManagementConfiguration {
}
}
3 JdbcTemplateConfiguration类分析
@Configuration
@Conditional(DataSourceAutoConfiguration.DataSourceAvailableCondition.class)
protected static class JdbcTemplateConfiguration {
@Autowired(required = false)
private DataSource dataSource;
@Bean
@ConditionalOnMissingBean(JdbcOperations.class)
//配置了一个JdbcTemplate
public JdbcTemplate jdbcTemplate() {
return new JdbcTemplate(this.dataSource);
}
@Bean
@ConditionalOnMissingBean(NamedParameterJdbcOperations.class)
public NamedParameterJdbcTemplate namedParameterJdbcTemplate() {
return new NamedParameterJdbcTemplate(this.dataSource);
}
}
4 DataSourceInitializer类分析
//该类提供初始化数据功能
class DataSourceInitializer implements ApplicationListener<DataSourceInitializedEvent> {
private static final Log logger = LogFactory.getLog(DataSourceInitializer.class);
@Autowired
private ConfigurableApplicationContext applicationContext;
private DataSource dataSource;
@Autowired
private DataSourceProperties properties;
private boolean initialized = false;
@PostConstruct
public void init() {
if (!this.properties.isInitialize()) {
logger.debug("Initialization disabled (not running DDL scripts)");
return;
}
if (this.applicationContext.getBeanNamesForType(DataSource.class, false,
false).length > 0) {
this.dataSource = this.applicationContext.getBean(DataSource.class);
}
if (this.dataSource == null) {
logger.debug("No DataSource found so not initializing");
return;
}
runSchemaScripts();
}
//放置在类路径下的schema.sql会自动用来初始化表结构
private void runSchemaScripts() {
List<Resource> scripts = getScripts(this.properties.getSchema(), "schema");
if (!scripts.isEmpty()) {
runScripts(scripts);
try {
this.applicationContext
.publishEvent(new DataSourceInitializedEvent(this.dataSource));
// The listener might not be registered yet, so don't rely on it.
if (!this.initialized) {
runDataScripts();
this.initialized = true;
}
}
catch (IllegalStateException ex) {
logger.warn("Could not send event to complete DataSource initialization ("
+ ex.getMessage() + ")");
}
}
}
@Override
public void onApplicationEvent(DataSourceInitializedEvent event) {
if (!this.properties.isInitialize()) {
logger.debug("Initialization disabled (not running data scripts)");
return;
}
// NOTE the event can happen more than once and
// the event datasource is not used here
if (!this.initialized) {
runDataScripts();
this.initialized = true;
}
}
//放置在类路径下的data.sql会自动用来填充表数据
private void runDataScripts() {
List<Resource> scripts = getScripts(this.properties.getData(), "data");
runScripts(scripts);
}
//获取执行sql脚本的名称
private List<Resource> getScripts(String locations, String fallback) {
if (locations == null) {
String platform = this.properties.getPlatform();
locations = "classpath*:" + fallback + "-" + platform + ".sql,";
locations += "classpath*:" + fallback + ".sql";
}
return getResources(locations);
}
private List<Resource> getResources(String locations) {
List<Resource> resources = new ArrayList<Resource>();
for (String location : StringUtils.commaDelimitedListToStringArray(locations)) {
try {
for (Resource resource : this.applicationContext.getResources(location)) {
if (resource.exists()) {
resources.add(resource);
}
}
}
catch (IOException ex) {
throw new IllegalStateException(
"Unable to load resource from " + location, ex);
}
}
return resources;
}
//运行脚本列表
private void runScripts(List<Resource> resources) {
if (resources.isEmpty()) {
return;
}
ResourceDatabasePopulator populator = new ResourceDatabasePopulator();
populator.setContinueOnError(this.properties.isContinueOnError());
populator.setSeparator(this.properties.getSeparator());
if (this.properties.getSqlScriptEncoding() != null) {
populator.setSqlScriptEncoding(this.properties.getSqlScriptEncoding().name());
}
for (Resource resource : resources) {
populator.addScript(resource);
}
DatabasePopulatorUtils.execute(populator, this.dataSource);
}
}