一般项目都会有自己的一套异常处理方式,sharding-jdbc也不以外,sharding-jdbc源码处理异常的方式主要有下面2种方式:
google-guava的Preconditions用于条件检查,不符合预期的话则抛出异常,并可以重写异常信息。google-guava源码中Preconditions的注释如下:
Static convenience methods that help a method or constructor check whether it was invoked correctly (whether its preconditions have been met). These methods generally accept a boolean expression which is expected to be true (or in the case of checkNotNull, an object reference which is expected to be non-null). When false (or null) is passed instead, the Preconditions method throws an unchecked exception, which helps the calling method communicate to its caller that that caller has made a mistake. 即帮助我们检查方法或者构造函数是否被正确调用,一般接收布尔表达式,期望布尔表达式的值为true;如果布尔表达式的值为false,就会抛出异常,让调用者知道错误的原因。
其部分static方法实现源码如下:
// Ensures the truth of an expression involving one or more parameters to the calling method.public static void checkArgument(boolean expression, @Nullable Object errorMessage) { if (!expression) { throw new IllegalArgumentException(String.valueOf(errorMessage)); }}
// Ensures the truth of an expression involving the state of the calling instance, but not involving any parameters to the calling method.public static void checkState(boolean expression, @Nullable Object errorMessage) { if (!expression) { throw new IllegalStateException(String.valueOf(errorMessage)); }}
// Ensures that an object reference passed as a parameter to the calling method is not null.public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) { if (reference == null) { throw new NullPointerException(String.valueOf(errorMessage)); } return reference;}
/** * Ensures that {@code index} specifies a valid <i>element</i> in an array, list or string of size * {@code size}. An element index may range from zero, inclusive, to {@code size}, exclusive. */public static int checkElementIndex( int index, int size, @Nullable String desc) { // Carefully optimized for execution by hotspot (explanatory comment above) if (index < 0 || index >= size) { throw new IndexOutOfBoundsException(badElementIndex(index, size, desc)); } return index;}
接下来我们看一下sharding-jdbc源码里张亮大神是如何使用Preconditions的:
@SuppressWarnings("unchecked")private <T extends ShardingStrategy> T buildShardingAlgorithmClassName(final List<String> shardingColumns, ... ...) { ... ... // 如果是SingleKeyShardingAlgorithm,那么sharding column只能有一个 if (shardingAlgorithm instanceof SingleKeyShardingAlgorithm) { Preconditions.checkArgument(1 == shardingColumns.size(), "Sharding-JDBC: SingleKeyShardingAlgorithm must have only ONE sharding column"); ... ... } ... ...}
private Collection<String> routeDataSources(final TableRule tableRule) { ... ... Collection<String> result = strategy.doStaticSharding(tableRule.getActualDatasourceNames(), shardingValues); // result是路由结果,即原生SQL路由后需要在哪些数据库中执行,很明显result肯定不可能为空; Preconditions.checkState(!result.isEmpty(), "no database route info"); return result;}
private static String getFromList(int index){ // 如果从集合中取数据, 首先校验下标 Preconditions.checkElementIndex(index, list.size(), "index is too big, list size is "+list.size()+". "); return list.get(index);}
总结:很明显,借助google_guava的Preconditions能够让我们的代码更优雅,更简洁;
sharding-jdbc自定义了异常处理类 ShardingJdbcException
:
public class ShardingJdbcException extends RuntimeException { // 异常类构造方法:异常信息errorMessage中有多个参数,例如:throw new ShardingJdbcException("Unsupported Date type:%s", convertType); public ShardingJdbcException(final String errorMessage, final Object... args) { super(String.format(errorMessage, args)); } // 把catch的异常转成ShardingJdbcException类型的异常,并重写异常信息 public ShardingJdbcException(final String message, final Exception cause) { super(message, cause); } // 把异常转成ShardingJdbcException类型的异常,不重写异常信息 public ShardingJdbcException(final Exception cause) { super(cause); }}
-- 抛出自定义异常并重写有参数的异常信息
if (result.isEmpty()) { throw new ShardingJdbcException("Cannot find table rule and default data source with logic tables: '%s'", logicTables);}
try { method.invoke(target, arguments);} catch (final IllegalAccessException | InvocationTargetException ex) { throw new ShardingJdbcException("Invoke jdbc method exception", ex);}
public static void handleException(final Exception exception) { if (isExceptionThrown()) { throw new ShardingJdbcException(exception); } log.error("exception occur: ", exception);}
sharding-jdbc对异常的处理还是很有参考价值的,自定义异常类型封装业务异常,我们一般都会这么做;但是如果能借鉴sharding-jdbc的源码,再增加对 Preconditions
的使用,很明显能够让代码的逼格提升不少^^; ```
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