spring事务管理现阶段主要通过三个重要接口规范，TransactionDefinition事务定义，主要定义事务的名称，传播属性，事务隔离级别，是否只读，超时时间等；TransactionStatus事务执行中的状态，主要封装保存事务执行过程中的数据及状态；TransactionManager事务管理器，管理事务的执行（开启事务，提交或回滚事务）。
TransactionDefiniton事务定义
TransactionDefiniton规范是通过jdk8以上采用默认方法实现。主要定义了事务的属性：
- 事务名称
- 事务传播行为
- 事务隔离级别
- 是否只读
- 执行超时时间
public interface TransactionDefinition {
// 7种事务传播行为
// 1.如果存在一个事务，则支持当前事务。如果没有事务则开启一个新的事务。
int PROPAGATION_REQUIRED = 0;
// 如果存在一个事务，支持当前事务。如果没有事务，则非事务的执行。但是对于事务同步的事务管理器，PROPAGATION_SUPPORTS与不使用事务有少许不同。
int PROPAGATION_SUPPORTS = 1;
// 如果已经存在一个事务，支持当前事务。如果没有一个活动的事务，则抛出异常。
int PROPAGATION_MANDATORY = 2;
// 开启一个新的事务。如果一个事务已经存在，则先将这个存在的事务挂起。
int PROPAGATION_REQUIRES_NEW = 3;
// 以非事务的方式运行，若当前存在事务，就挂起当前事务
int PROPAGATION_NOT_SUPPORTED = 4;
// 总是非事务地执行，并挂起任何存在的事务
int PROPAGATION_NEVER = 5;
// 如果一个活动的事务存在，则运行在一个嵌套的事务中。 如果没有活动事务, 则按TransactionDefinition.PROPAGATION_REQUIRED 属性执行。
int PROPAGATION_NESTED = 6;
int ISOLATION_DEFAULT = -1;// 默认使用数据库隔离级别
int ISOLATION_READ_UNCOMMITTED = 1; // same as java.sql.Connection.TRANSACTION_READ_UNCOMMITTED;
int ISOLATION_READ_COMMITTED = 2; // same as java.sql.Connection.TRANSACTION_READ_COMMITTED;
int ISOLATION_REPEATABLE_READ = 4; // same as java.sql.Connection.TRANSACTION_REPEATABLE_READ;
int ISOLATION_SERIALIZABLE = 8; // same as java.sql.Connection.TRANSACTION_SERIALIZABLE;
int TIMEOUT_DEFAULT = -1;
default int getPropagationBehavior() {
return PROPAGATION_REQUIRED;
}
default int getIsolationLevel() {
return ISOLATION_DEFAULT;
}
default int getTimeout() {
return TIMEOUT_DEFAULT;
}
default boolean isReadonly() {
return false;
}
@Nullable
default String getName() {
return null;
}
static TransactionDefinition withDefaults() {
return StaticTransactionDefinition.INSTANCE;
}
}
TransactionDefinition UML
public class DefaultTransactionDefinition implements TransactionDefinition, Serializable {
private int propagationBehavior = PROPAGATION_REQUIRED;
private int isolationLevel = ISOLATION_DEFAULT;
private int timeout = TIMEOUT_DEFAULT;
private boolean readonly = false;
@Nullable
private String name;
}
DefaultTransactionDefinition默认事务定义中定义了属性规范中的属性字段。
TransactionAttribute定义
TransactionAttribute继承了TransactionDefinition增加了一些标签属性及rollbackOn字段。
public interface TransactionAttribute extends TransactionDefinition {
@Nullable
String getQualifier();
Collection getLabels();
boolean rollbackOn(Throwable ex);
}
TransactionStatus事务运行状态
TransactionStatus主要作为事务运行时载体，保存着事务信息，事务的状态。
public interface SavepointManager {
Object createSavepoint() throws TransactionException;
void rollbackToSavepoint(Object savepoint) throws TransactionException;
void releaseSavepoint(Object savepoint) throws TransactionException;
}
public interface TransactionExecution {
boolean isNewTransaction();
void setRollbackonly();
boolean isRollbackonly();
boolean isCompleted();
}
// 主要组合了保存点规范（SavepointManager）及执行中状态规范（TransactionExecution）
public interface TransactionStatus extends TransactionExecution, SavepointManager, Flushable {
boolean hasSavepoint();
@Override
void flush();
}
DefaultTransactionStatus默认实现
抽象实现
public abstract class AbstractTransactionStatus implements TransactionStatus {
private boolean rollbackonly = false;
private boolean completed = false;
@Nullable
private Object savepoint;
// --------------对savePoint的操作----------------------
public void createAndHoldSavepoint() throws TransactionException {
setSavepoint(getSavepointManager().createSavepoint());
}
public void rollbackToHeldSavepoint() throws TransactionException {
Object savepoint = getSavepoint();
if (savepoint == null) {
throw new TransactionUsageException("Cannot roll back to savepoint - no savepoint associated with current transaction");
}
getSavepointManager().rollbackToSavepoint(savepoint);
getSavepointManager().releaseSavepoint(savepoint);
setSavepoint(null);
}
public void releaseHeldSavepoint() throws TransactionException {
Object savepoint = getSavepoint();
if (savepoint == null) {
throw new TransactionUsageException("Cannot release savepoint - no savepoint associated with current transaction");
}
getSavepointManager().releaseSavepoint(savepoint);
setSavepoint(null);
}
//---------------------------------------------------------------------
// Implementation of SavepointManager
//---------------------------------------------------------------------
@Override
public Object createSavepoint() throws TransactionException {
return getSavepointManager().createSavepoint();
}
@Override
public void rollbackToSavepoint(Object savepoint) throws TransactionException {
getSavepointManager().rollbackToSavepoint(savepoint);
}
@Override
public void releaseSavepoint(Object savepoint) throws TransactionException {
getSavepointManager().releaseSavepoint(savepoint);
}
}
默认实现：
public class DefaultTransactionStatus extends AbstractTransactionStatus {
@Nullable
private final Object transaction;// 底层具体事务对象（封装了连接等）
private final boolean newTransaction;//是否是新开启的事务（=true时才会提交事务）
private final boolean newSynchronization;// 是否是新建的同步器（=true时才会执行回调事件）
private final boolean readOnly;
// 挂起的资源信息（事务传播行为要求挂起当前事务时，挂起的事务暂存信息，执行完后用于恢复）
@Nullable
private final Object suspendedResources;
public DefaultTransactionStatus(
@Nullable Object transaction, boolean newTransaction, boolean newSynchronization,
boolean readOnly, boolean debug, @Nullable Object suspendedResources) {
this.transaction = transaction;
this.newTransaction = newTransaction;
this.newSynchronization = newSynchronization;
this.readonly = readOnly;
this.debug = debug;
this.suspendedResources = suspendedResources;
}
}
TransactionManager事务管理器
TransactionManager事务管理器，主要管理spring的事务传播行为，事务的开始，提交或回滚，以及诸多事务执行过程中的事件监听机制。
public interface TransactionManager {
// TransactionManager只是一个标记接口
}
//
public interface PlatformTransactionManager extends TransactionManager {
// 根据事务的定义，创建事务并返回事务运行状态对象
TransactionStatus getTransaction(@Nullable TransactionDefinition definition) throws TransactionException;
// 提交或回滚
void commit(TransactionStatus status) throws TransactionException;
void rollback(TransactionStatus status) throws TransactionException;
}
事务管理器的实现模板在于AbstractPlatformTransactionManager，在这个类中提供了事务的开启，事务传播行为的执行，事务挂起提交等模板方法的封装，参见AbstractPlatformTransactionManager详解
