javax.sql.rowset.spi (Java Platform SE 8 )

接口摘要
接口	描述
SyncResolver	定义一个框架，允许应用程序使用手动决策树来决定在发生同步冲突时应该做什么。
TransactionalWriter	一个专门的界面，有助于扩展标准的 `SyncProvider`抽象类，使其具有更细粒度的事务控制。
XmlReader	一种专门的界面，有助于扩展面向XML的同步提供程序的 `SyncProvider`抽象类。
XmlWriter	一种专门的界面，有助于扩展面向XML的同步提供程序的 `SyncProvider`抽象类。

类摘要
类	描述
SyncFactory	服务提供者接口（SPI）机制，可生成 `SyncProvider`实例，由断开的 `RowSet`对象使用。
SyncProvider	同步机制，为断开 `RowSet`对象提供读写器功能。

异常摘要
异常	描述
SyncFactoryException	表示有错误 `SyncFactory`机制。
SyncProviderException	表示与错误 `SyncProvider`机制。

Package javax.sql.rowset.spi Description

第三方供应商在实施同步提供程序时必须使用的标准类和接口。这些类和接口被称为服务提供者接口（SPI）。供应商可能通过发送电子邮件到jdbc@sun.com ，将其实现包含在JDBC网页上，其中列出了可用的SyncProvider jdbc@sun.com 。这样做有助于使开发人员了解实施。为了使一个RowSet对象可以使用一个实现，供应商必须注册它与SyncFactory单例。（有关注册过程的完整说明和要使用的命名约定，请参阅SyncProvider的类注释。）

A SyncProvider implementation provides a disconnected RowSet object with the mechanisms for reading data into it and for writing data that has been modified in it back to the underlying data source. A reader, a RowSetReader or XMLReader object, reads data into a RowSet object when the CachedRowSet methods execute or populate are called. A writer, a RowSetWriter or XMLWriter object, writes changes back to the underlying data source when the CachedRowSet method acceptChanges is called.

The process of writing changes in a RowSet object to its data source is known as synchronization. The SyncProvider implementation that a RowSet object is using determines the level of synchronization that the RowSet object's writer uses. The various levels of synchronization are referred to as grades.

The lower grades of synchronization are known as optimistic concurrency levels because they optimistically assume that there will be no conflicts or very few conflicts. A conflict exists when the same data modified in the RowSet object has also been modified in the data source. Using the optimistic concurrency model means that if there is a conflict, modifications to either the data source or the RowSet object will be lost.

Higher grades of synchronization are called pessimistic because they assume that others will be accessing the data source and making modifications. These grades set varying levels of locks to increase the chances that no conflicts occur.

The lowest level of synchronization is simply writing any changes made to the RowSet object to its underlying data source. The writer does nothing to check for conflicts. If there is a conflict and the data source values are overwritten, the changes other parties have made by to the data source are lost.

The RIXMLProvider implementation uses the lowest level of synchronization and just writes RowSet changes to the data source. This is true because typically XML data sources do not enable transaction techniques for maintaining the integrity of data. However, specific standards groups have considered offering XML-based synchronization. For details, see

   http://www.syncml.org

对于下一个级别，作者检查是否有任何冲突，如果有的话，它不会对数据源写任何东西。这种并发级别的问题是，如果RowSet对象得到其数据，如果另一方修改了数据源中的RowSet数据，那么对RowSet对象所做的更改将丢失。 RIOptimisticProvider实现使用这种级别的同步。

在较高级别的同步，称为悲观并发，作者采取措施通过设置锁来避免冲突。设置锁可以从设置单个行的锁定到在表或整个数据源上设置锁定而有所不同。因此，同步级别是用户同时访问数据源的能力与作者将数据保持在RowSet对象及其数据源同步的能力之间的折衷。

这是所有断开的要求RowSet对象（ CachedRowSet ， FilteredRowSet ， JoinRowSet和WebRowSet对象）获得其SyncProvider从对象SyncFactory机制。

参考实现（RI）提供了两个同步提供程序。

RIOptimisticProvider
SyncFactory实例在未指定提供程序实现时将提供给断开RowSet对象的默认提供程序。
该同步提供程序使用乐观并发模型，假设在数据库中访问相同数据的用户之间将存在很少的冲突。它避免使用锁; 而是在尝试同步RowSet对象和数据源之前检查是否存在冲突。如果有冲突，它什么都不做，这意味着RowSet对象的更改不会持久保留到数据源。
RIXMLProvider
可与WebRowSet对象一起使用的同步提供程序，该对象是可以以XML格式编写或从XML格式读取的行集。 RIXMLProvider实现不会检查冲突，只需将WebRowSet对象中的任何更新的数据写入底层数据源。 WebRowSet对象在处理XML数据时使用此提供程序。

这些SyncProvider实现与SyncProvider实现捆绑在一起，这使得它们始终可用于RowSet实现。 SyncProvider实现使自己可以通过与注册SyncFactory单。当一个RowSet对象请求一个提供者时，通过在构造函数中指定它或CachedRowSet方法setSyncProvider的参数， SyncFactory单例检查以查看请求的提供者是否已经注册。如果有的话， SyncFactory创建一个实例，并将其传递给请求的RowSet对象。如果指定的SyncProvider实现尚未注册，则SyncFactory单例会导致抛出SyncFactoryException对象。如果没有指定提供者，SyncFactory SyncFactory例将创建默认提供程序实现的实例RIOptimisticProvider ，并将其传递给请求的RowSet对象。

如果一个WebRowSet对象在其WebRowSet函数中没有指定提供者，则SyncFactory将给它一个RIOptimisticProvider的实例。但是，WebRowSet的WebRowSet被实现以将提供者设置为RIXMLProvider ，它以XML格式读取和写入RowSet对象。

有关详细信息，请参阅SyncProvider类规范。

供应商可以开发一个SyncProvider实现与同步的可能级别中的任何一个，从而使RowSet对象的同步机制的选择。供应商可以通过向甲骨文公司注册完全合格的类名，从而使其实现可用，方法是： jdbc@sun.com 。以下进一步详细讨论该过程。

2.0 Service Provider Interface Architecture

2.1 Overview

The Service Provider Interface provides a pluggable mechanism by which SyncProvider implementations can be registered and then generated when required. The lazy reference mechanism employed by the SyncFactory limits unnecessary resource consumption by not creating an instance until it is required by a disconnected RowSet object. The SyncFactory class also provides a standard API to configure logging options and streams that may be provided by a particular SyncProvider implementation.

2.2 Registering with the SyncFactory

A third party SyncProvider implementation must be registered with the SyncFactory in order for a disconnected RowSet object to obtain it and thereby use its javax.sql.RowSetReader and javax.sql.RowSetWriter implementations. The following registration mechanisms are available to all SyncProvider implementations:

System properties - Properties set at the command line. These properties are set at run time and apply system-wide per invocation of the Java application. See the section "Related Documentation" further related information.
Property Files - Properties specified in a standard property file. This can be specified using a System Property or by modifying a standard property file located in the platform run-time. The reference implementation of this technology includes a standard property file than can be edited to add additional SyncProvider objects.
JNDI Context - Available providers can be registered on a JNDI context. The SyncFactory will attempt to load SyncProvider objects bound to the context and register them with the factory. This context must be supplied to the SyncFactory for the mechanism to function correctly.

有关如何指定属性文件中的系统属性或属性以及如何配置JNDI上下文的详细信息，请参见SyncFactory类描述。

2.3 SyncFactory Provider实例生成策略

SyncFactory如果提供程序已SyncFactory注册，则生成请求的SyncProvider对象。以下策略粘附当任一个断开，以RowSet对象与指定实例SyncProvider实现或在运行时被重新配置具有替代SyncProvider对象。

如果SyncProvider指定对象和SyncFactory 没有提及供应商，一个SyncFactoryException被抛出。
如果指定了SyncProvider对象，并且SyncFactory包含对提供程序的引用，则提供请求的提供程序。
如果没有SyncProvider对象，则提供参考实现提供者RIOptimisticProvider 。

这些政策在SyncFactory课程中有更详细的探讨。

3.0 SyncProvider Implementer's Guide

3.1 Requirements

A compliant SyncProvider implementation that is fully pluggable into the SyncFactory must extend and implement all abstract methods in the SyncProvider class. In addition, an implementation must determine the grade, locking and updatable view capabilities defined in the SyncProvider class definition. One or more of the SyncProvider description criteria must be supported. It is expected that vendor implementations will offer a range of grade, locking, and updatable view capabilities.

此外， SyncProvider命名约定必须遵循SyncProvider类描述中的详细说明。

3.2年级

JSR 114定义了一组等级来描述同步的质量，一个SyncProvider对象可以提供一个断开的RowSet对象。这些等级从最低服务质量列为最高。

GRADE_NONE - 不提供与始发数据源的同步。一个SyncProvider实现返回此等级将简单的写在改变任何数据RowSet对象的基础数据源，覆盖不管是存在的。没有尝试将原始值与当前值进行比较，以查看是否存在冲突。 RIXMLProvider是用这个档次实现的。
GRADE_CHECK_MODIFIED_AT_COMMIT - 低级别的乐观同步。一个SyncProvider实现返回此等级将检查行已经过去的同步和正在进行的当前同步之间更改冲突。已修改的始发数据源中的任何更改都不会反映在断开RowSet对象中。如果没有冲突， RowSet对象中的更改将被写入数据源。如果有冲突，则不会改变。 RIOptimisticProvider实现使用这个等级。
GRADE_CHECK_ALL_AT_COMMIT - 高度的乐观同步。一个SyncProvider实现返回此等级将检查所有的行，包括那些没有在断开更改的行RowSet对象。以这种方式，当同步完成成功时，底层数据源中对行的任何更改将反映在断开RowSet对象中。
GRADE_LOCK_WHEN_MODIFIED - 悲观的同步档次。 SyncProvider此等级的SyncProvider实现将锁定与RowSet对象中正在更改的行对应的始发数据源中的行，以减少其他进程修改数据源中相同数据的可能性。
GRADE_LOCK_WHEN_LOADED - 较高的悲观同步等级。甲SyncProvider执行返回此等级将锁定受用于填充原始查询整个视图和/或表RowSet对象。

3.3锁

JSR 114定义了一组常量，它们指定是否将任何锁放置在RowSet对象的基础数据源上，如果是这样，则在其上放置锁的结构。这些锁将保留在数据源上，而RowSet对象与数据源断开连接。

这些常数应该被认为是等级常数的补充。大多数成绩设置的默认设置要求当RowSet对象与其数据源断开连接时，不会保留数据源锁。等级GRADE_LOCK_WHEN_MODIFIED和GRADE_LOCK_WHEN_LOADED允许断开的RowSet对象对锁定程度进行细粒度控制。

DATASOURCE_NO_LOCK - 始发数据源上没有锁。这是所有SyncProvider实现的默认锁定设置，除非RowSet对象另有指示。
DATASOURCE_ROW_LOCK - 锁被放置在用于填充RowSet对象的原始SQL查询所触摸的行上。
DATASOURCE_TABLE_LOCK - 锁定被放置在用于填充RowSet对象的查询所触及的所有表上。
DATASOURCE_DB_LOCK在RowSet对象使用的整个数据源上放置一个锁。

3.4可更新视图

可以使用来自SQL VIEW数据RowSet对象。以下常量指示是否SyncProvider对象可以更新表中或从该表中的数据VIEW推导。

UPDATABLE_VIEW_SYNC表示一个SyncProvider实现支持同步到VIEW用于填充对象的SQL RowSet对象的表。
NONUPDATABLE_VIEW_SYNC表示一个SyncProvider实现不支持同步从该SQL表或表VIEW用于填充RowSet对象导出。

3.5使用SyncProvider分级和锁定

在下面的示例中，参考CachedRowSetImpl实现通过调用setSyncProvider方法重新配置其当前的SyncProvider对象。

  CachedRowSetImpl crs = new CachedRowSetImpl();
    crs.setSyncProvider("com.foo.bar.HASyncProvider");

应用程序可以检索由断开连接的RowSet对象当前正在使用的RowSet对象。

它还可以检索提供者实现的同步级别和当前使用的锁定程度。

此外，应用程序具有设置要使用的锁定程度的灵活性，这可以增加成功同步的可能性。

这些操作显示在以下代码片段中。

  SyncProvider sync = crs.getSyncProvider();

    switch (sync.getProviderGrade()) {
    case: SyncProvider.GRADE_CHECK_ALL_AT_COMMIT
         //A high grade of optimistic synchronization
    break;
    case: SyncProvider.GRADE_CHECK_MODIFIED_AT_COMMIT 
         //A low grade of optimistic synchronization 
    break;
    case: SyncProvider.GRADE_LOCK_WHEN_LOADED 
         // A pessimistic synchronization grade 
    break;
    case: SyncProvider.GRADE_LOCK_WHEN_MODIFIED 
         // A pessimistic synchronization grade 
    break;
    case: SyncProvider.GRADE_NONE 
      // No synchronization with the originating data source provided
    break;
    }
          
    switch (sync.getDataSourcLock() {
      case: SyncProvider.DATASOURCE_DB_LOCK
       // A lock is placed on the entire datasource that is used by the
       // RowSet object 
       break;

      case: SyncProvider.DATASOURCE_NO_LOCK
       // No locks remain on the  originating data source.
      break;

      case: SyncProvider.DATASOURCE_ROW_LOCK
       // A lock is placed on the rows that are  touched by the original 
       // SQL statement used to populate
       // the RowSet object that is using the SyncProvider
       break;

      case: DATASOURCE_TABLE_LOCK
       // A lock is placed on  all tables that are touched by the original 
       // SQL statement used to populated
       // the RowSet object that is using the SyncProvider
       break;

它使用的静态实用方法，也可以SyncFactory类确定的名单SyncProvider当前与注册的实现SyncFactory 。

  Enumeration e = SyncFactory.getRegisteredProviders();

4.0 Resolving Synchronization Conflicts

The interface SyncResolver provides a way for an application to decide manually what to do when a conflict occurs. When the CachedRowSet method acceptChanges finishes and has detected one or more conflicts, it throws a SyncProviderException object. An application can catch the exception and have it retrieve a SyncResolver object by calling the method SyncProviderException.getSyncResolver().

A SyncResolver object, which is a special kind of CachedRowSet object or a JdbcRowSet object that has implemented the SyncResolver interface, examines the conflicts row by row. It is a duplicate of the RowSet object being synchronized except that it contains only the data from the data source this is causing a conflict. All of the other column values are set to null. To navigate from one conflict value to another, a SyncResolver object provides the methods nextConflict and previousConflict.

The SyncResolver interface also provides methods for doing the following:

finding out whether the conflict involved an update, a delete, or an insert
getting the value in the data source that caused the conflict
setting the value that should be in the data source if it needs to be changed or setting the value that should be in the RowSet object if it needs to be changed

When the CachedRowSet method acceptChanges is called, it delegates to the RowSet object's SyncProvider object. How the writer provided by that SyncProvider object is implemented determines what level (grade) of checking for conflicts will be done. After all checking for conflicts is completed and one or more conflicts has been found, the method acceptChanges throws a SyncProviderException object. The application can catch the exception and use it to obtain a SyncResolver object.

The application can then use SyncResolver methods to get information about each conflict and decide what to do. If the application logic or the user decides that a value in the RowSet object should be the one to persist, the application or user can overwrite the data source value with it.

The comment for the SyncResolver interface has more detail.

5.0 Related Specifications

JNDI 1.3

Java Logging APIs

6.0 Related Documentation

System properties

资源文件
DataSource for JDBC Connections

Package javax.sql.rowset.spi