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14. sharding-jdbc源码之异常处理

96
阿飞Javaer
2018.04.23 10:13* 字数 630

阿飞Javaer,转载请注明原创出处,谢谢!

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:

  1. Preconditions
  2. 自定义异常

1. Preconditions

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:

  • 检查参数是否正确--expression就是判断方法的参数的表达式,errorMessage是自定义异常,不允许为空;
// 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));
    }
}
  • 检查状态是否正确--expression就是判断状态的参数的表达式,errorMessage是自定义异常,不允许为空;
// 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));
    }
}
  • 检查不允许为空--reference就是待检查参数,errorMessage是自定义异常,不允许为空;
// 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;
}
  • 检查下标是否越界--index就是待检查下标参数,size就是集合的size,errorMessage是自定义异常,不允许为空;
/**
 * 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:

  1. Preconditions.checkArgument()的使用
    源码如下:
@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");
        ... ...
    }
    ... ...
}
  1. Preconditions.checkState()的使用
    源码如下:
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;
}
  1. Preconditions.checkElementIndex()的使用
    源码如下(不是来自sharding-jdbc源码中,而是笔者写的):
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;

2. 自定义异常

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);
    }
}

sharding-jdbc中抛出自定义日志场景

-- 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);
}
  • 将IllegalAccessException或者InvocationTargetException类型的异常转化为ShardingJdbcException异常,并重写异常信息为"Invoke jdbc method exception"
try {
    method.invoke(target, arguments);
} catch (final IllegalAccessException | InvocationTargetException ex) {
    throw new ShardingJdbcException("Invoke jdbc method exception", ex);
}
  • 把异常转成ShardingJdbcException类型的异常,不重写异常信息
public static void handleException(final Exception exception) {
    if (isExceptionThrown()) {
        throw new ShardingJdbcException(exception);
    }
    log.error("exception occur: ", exception);
}

总结

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^^;

sharding-jdbc
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