Guava-retrying重试机制
转载于：https://blog.csdn.net/aitangyong/article/details/53889036
guava-retrying提供了WaitStrategy接口，用来控制2次重试的时间间隔，这个接口与StopStrategy有的类似。内置的等待策略在WaitStrategies中定义。
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import java.io.IOException;
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import java.text.SimpleDateFormat;
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import java.util.Date;
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import java.util.concurrent.Callable;
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public
class
AlwaysExceptionTask
implements
Callable
{
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-
private
static
final
SimpleDateFormat
df
=
new
SimpleDateFormat(
"yyyy-MM-dd hh:mm:ss,SSS");
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private
int
times
=
1;
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-
@Override
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public Boolean
call
()
throws Exception {
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System.out.println(df.format(
new
Date()));
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int
thisTimes
= times;
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times++;
-
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if (thisTimes ==
1) {
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throw
new
NullPointerException();
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}
else
if (thisTimes ==
2) {
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throw
new
IOException();
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}
else
if (thisTimes ==
3) {
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throw
new
ArithmeticException();
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}
else {
-
throw
new
Exception();
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}
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}
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}
WaitStrategies.noWait()失败后立刻重试，没有等待时间。
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Retryer
retryer = RetryerBuilder.newBuilder()
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.retryIfException()
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.withWaitStrategy(WaitStrategies.noWait())
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.build();
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System.out.println(
"begin..." + df.format(
new
Date()));
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-
try {
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retryer.call(
new
AlwaysExceptionTask());
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}
catch (Exception e) {
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System.err.println(
"still failed after retry." + e.getCause().toString());
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}
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System.out.println(
"end..." + df.format(
new
Date()));
WaitStrategies.fixedWait(1, TimeUnit.SECONDS)间隔固定时间之后重试，比如每隔1s重试一次。
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Retryer
retryer = RetryerBuilder.newBuilder()
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.retryIfException()
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.withWaitStrategy(WaitStrategies.fixedWait(
1, TimeUnit.SECONDS))
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.build();
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System.out.println(
"begin..." + df.format(
new
Date()));
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try {
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retryer.call(
new
AlwaysExceptionTask());
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}
catch (Exception e) {
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System.err.println(
"still failed after retry." + e.getCause().toString());
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}
WaitStrategies.randomWait(3, TimeUnit.SECONDS)间隔随机时间后重试，比如间隔0~3中随机时间后重试。
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Retryer
retryer = RetryerBuilder.newBuilder()
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.retryIfException()
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.withWaitStrategy(WaitStrategies.randomWait(
3, TimeUnit.SECONDS))
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.build();
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System.out.println(
"begin..." + df.format(
new
Date()));
-
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try {
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retryer.call(
new
AlwaysExceptionTask());
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}
catch (Exception e) {
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System.err.println(
"still failed after retry." + e.getCause().toString());
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}
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System.out.println(
"end..." + df.format(
new
Date()));
WaitStrategies.randomWait(2, TimeUnit.SECONDS, 5, TimeUnit.SECONDS)最小值，最大值之间的随机时间。
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Retryer
retryer = RetryerBuilder.newBuilder()
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.retryIfException()
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.withWaitStrategy(WaitStrategies.randomWait(
2, TimeUnit.SECONDS,
5, TimeUnit.SECONDS))
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.build();
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System.out.println(
"begin..." + df.format(
new
Date()));
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try {
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retryer.call(
new
AlwaysExceptionTask());
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}
catch (Exception e) {
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System.err.println(
"still failed after retry." + e.getCause().toString());
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}
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System.out.println(
"end..." + df.format(
new
Date()));
WaitStrategies.incrementingWait增量重试，重试的次数越多，等待时间间隔越长。incrementingWait需要传递2个参数，一个是initialSleepTime(第一次到第二次尝试的间隔)，一个是increment(每增加一次尝试，需要增加的时间间隔)。第一次尝试是不需要等待的，因为guava-retrying中的第一次尝试，对应正常的第一次调用。从第二次重试开始，第n-1次到n次间隔是：initialSleepTime + (n-2)*increment。
1、WaitStrategies.incrementingWait(0, TimeUnit.SECONDS, 0, TimeUnit.SECONDS)等价于 WaitStrategies.noWait()。
2、 WaitStrategies.incrementingWait(1, TimeUnit.SECONDS, 0, TimeUnit.SECONDS)等价于WaitStrategies.fixedWait(1, TimeUnit.SECONDS)
3、 WaitStrategies.incrementingWait(0, TimeUnit.SECONDS, 1, TimeUnit.SECONDS)等价于WaitStrategies.fixedWait(1, TimeUnit.SECONDS)。
4、 WaitStrategies.incrementingWait(1, TimeUnit.SECONDS, 1, TimeUnit.SECONDS)
WaitStrategies.fibonacciWait()按照斐波那契数列等待。fibonacciWait(long multiplier,long maximumTime,TimeUnit maximumTimeUnit)，multiplier单位固定是ms，maximumTime最大等待时间。n=1的时候，是无需等待的。当n>=2的时候，开始符合斐波那契数列。n=2的时候，等待1 * multiplier毫秒；n=3的时候，等待1 * multiplier毫秒；n=4的时候，等待2 * multiplier毫秒；n=5的时候，等待3 * multiplier毫秒；n=6的时候，等待5 * multiplier毫秒；n=7的时候，等待8 * multiplier毫秒；n=8的时候，等待15 * multiplier毫秒；......但是等待时间最长不超过maximumTime。
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Retryer
retryer = RetryerBuilder.newBuilder()
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.retryIfException()
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.withWaitStrategy(WaitStrategies.fibonacciWait(
100,
10, TimeUnit.SECONDS))
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.build();
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System.out.println(
"begin..." + df.format(
new
Date()));
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try {
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retryer.call(
new
AlwaysExceptionTask());
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}
catch (Exception e) {
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System.err.println(
"still failed after retry." + e.getCause().toString());
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}
WaitStrategies.exponentialWait按照指数递增(2的n次方)来等待，各个参数含义与fibonacciWait相同。
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Retryer
retryer = RetryerBuilder.newBuilder()
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.retryIfException()
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.withWaitStrategy(WaitStrategies.exponentialWait(
100,
10, TimeUnit.SECONDS))
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.build();
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System.out.println(
"begin..." + df.format(
new
Date()));
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try {
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retryer.call(
new
AlwaysExceptionTask());
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}
catch (Exception e) {
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System.err.println(
"still failed after retry." + e.getCause().toString());
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}
WaitStrategies.exceptionWait根据抛出的异常来决定等待的时间长短，没有什么实际用处，不过作为学习还是可以了解下，说不定将来能排上用场呢。下面我们定义1个任务，随机抛出不同异常。
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class
RandomExceptionTask
implements
Callable
{
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@Override
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public Boolean
call
()
throws Exception {
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int
round
= (
int) Math.floor(Math.random() *
8);
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System.out.println(
"round=" + round +
",time=" + df.format(
new
Date()));
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if (round ==
1) {
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throw
new
NullPointerException();
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}
else
if (round ==
2) {
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throw
new
IOException();
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}
else
if (round ==
3) {
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throw
new
ArithmeticException();
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}
else
if (round ==
4) {
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throw
new
IllegalStateException();
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}
else
if (round ==
5) {
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throw
new
IndexOutOfBoundsException();
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}
else {
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return
true;
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}
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}
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}
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// 根据不同异常,等待不同时间后重试
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private
static
extends
Throwable> Function
itsFunction
(Class exceptionClass) {
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Function
result =
new
Function() {
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@Nullable
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@Override
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public Long
apply
(@Nullable T input) {
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if (input
instanceof NullPointerException) {
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return
1 *
1000L;
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}
else
if (input
instanceof IOException) {
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return
2 *
1000L;
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}
else
if (input
instanceof ArithmeticException) {
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return
3 *
1000L;
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}
else
if (input
instanceof IllegalStateException) {
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return
4 *
1000L;
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}
else
if (input
instanceof IndexOutOfBoundsException) {
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return
5 *
1000L;
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}
else {
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return
0L;
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}
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}
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};
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return result;
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}
下面是测试代码，可以看出不同的异常确实会导致不同的重试间隔。
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WaitStrategy
exceptionJoin
= WaitStrategies.join(
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WaitStrategies.exceptionWait(NullPointerException.class, itsFunction(NullPointerException.class)),
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WaitStrategies.exceptionWait(IOException.class, itsFunction(IOException.class)),
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WaitStrategies.exceptionWait(ArithmeticException.class, itsFunction(ArithmeticException.class)),
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WaitStrategies.exceptionWait(IllegalStateException.class, itsFunction(IllegalStateException.class)),
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WaitStrategies.exceptionWait(IndexOutOfBoundsException.class, itsFunction(IndexOutOfBoundsException.class))
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);
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Retryer
retryer = RetryerBuilder.newBuilder()
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.retryIfException()
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.withWaitStrategy(exceptionJoin)
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.build();
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System.out.println(
"begin..." + df.format(
new
Date()));
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try {
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retryer.call(
new
RandomExceptionTask());
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}
catch (Exception e) {
-
System.err.println(
"still failed after retry." + e.getCause().toString());
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}
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System.out.println(
"end..." + df.format(
new
Date()));
