org.h2.util

Class Utils

java.lang.Object

org.h2.util.Utils

public class Utils
extends java.lang.Object

This utility class contains miscellaneous functions.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Utils.ClassFactory The utility methods will try to use the provided class factories to convert binary name of class to Class object.

Field Summary

Fields

Modifier and Type	Field and Description
static byte[]	EMPTY_BYTES An 0-size byte array.
static int[]	EMPTY_INT_ARRAY An 0-size int array.

Method Summary

Modifier and Type	Method and Description
static java.lang.Object	callMethod(java.lang.Object instance, java.lang.String methodName, java.lang.Object... params) Calls an instance method via reflection.
static java.lang.Object	callStaticMethod(java.lang.String classAndMethod, java.lang.Object... params) Calls a static method via reflection.
static byte[]	cloneByteArray(byte[] b) Create a new byte array and copy all the data.
static void	collectGarbage() Run Java memory garbage collection.
static boolean	compareSecure(byte[] test, byte[] good) Compare two byte arrays.
static byte[]	copy(byte[] source, byte[] target) Copy the contents of the source array to the target array.
static byte[]	copyBytes(byte[] bytes, int len) Creates a copy of array of bytes with the new size.
static java.util.concurrent.ThreadPoolExecutor	createSingleThreadExecutor(java.lang.String threadName)
static java.util.concurrent.ThreadPoolExecutor	createSingleThreadExecutor(java.lang.String threadName, java.util.concurrent.BlockingQueue<java.lang.Runnable> workQueue)
static long	currentNanoTime() Returns the current value of the high-resolution time source.
static long	currentNanoTimePlusMillis(int ms) Returns the current value of the high-resolution time source plus the specified offset.
static void	flushExecutor(java.util.concurrent.ThreadPoolExecutor executor) Makes sure that all currently submitted tasks are processed before this method returns.
static int	getByteArrayHash(byte[] value) Calculate the hash code of the given byte array.
static long	getGarbageCollectionCount()
static long	getGarbageCollectionTime()
static long	getMemoryFree() Get the free memory in KB.
static long	getMemoryMax() Get the maximum memory in KB.
static long	getMemoryUsed() Get the used memory in KB.
static java.lang.Class<?>	getNonPrimitiveClass(java.lang.Class<?> clazz) Convert primitive class names to java.lang.* class names.
static boolean	getProperty(java.lang.String key, boolean defaultValue) Get the system property.
static int	getProperty(java.lang.String key, int defaultValue) Get the system property.
static java.lang.String	getProperty(java.lang.String key, java.lang.String defaultValue) Get the system property.
static byte[]	getResource(java.lang.String name) Get a resource from the resource map.
static int	indexOf(byte[] bytes, byte[] pattern, int start) Calculate the index of the first occurrence of the pattern in the byte array, starting with the given index.
static long	nanoTimePlusMillis(long nanoTime, int ms) Returns the current value of the high-resolution time source plus the specified offset.
static byte[]	newBytes(int len) Create an array of bytes with the given size.
static java.lang.Object	newInstance(java.lang.String className, java.lang.Object... params) Creates a new instance.
static <T> java.util.ArrayList<T>	newSmallArrayList() Create a new ArrayList with an initial capacity of 4.
static boolean	parseBoolean(java.lang.String value, boolean defaultValue, boolean throwException) Parses the specified string to boolean value.
static int	scaleForAvailableMemory(int value) Scale the value with the available memory.
static void	shutdownExecutor(java.util.concurrent.ThreadPoolExecutor executor)
static <X> void	sortTopN(X[] array, int fromInclusive, int toExclusive, java.util.Comparator<? super X> comp) Find the top limit values using given comparator and place them as in a full array sort, in descending order.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

EMPTY_BYTES

public static final byte[] EMPTY_BYTES

An 0-size byte array.

EMPTY_INT_ARRAY

public static final int[] EMPTY_INT_ARRAY

An 0-size int array.

Method Detail

indexOf

public static int indexOf(byte[] bytes,
                          byte[] pattern,
                          int start)

Calculate the index of the first occurrence of the pattern in the byte array, starting with the given index. This methods returns -1 if the pattern has not been found, and the start position if the pattern is empty.

Parameters:

bytes - the byte array

pattern - the pattern

start - the start index from where to search

Returns:

the index

getByteArrayHash

public static int getByteArrayHash(byte[] value)

Calculate the hash code of the given byte array.

Parameters:

value - the byte array

Returns:

the hash code

compareSecure

public static boolean compareSecure(byte[] test,
                                    byte[] good)

Compare two byte arrays. This method will always loop over all bytes and doesn't use conditional operations in the loop to make sure an attacker can not use a timing attack when trying out passwords.

Parameters:

test - the first array

good - the second array

Returns:

true if both byte arrays contain the same bytes

copy

public static byte[] copy(byte[] source,
                          byte[] target)

Copy the contents of the source array to the target array. If the size if the target array is too small, a larger array is created.

Parameters:

source - the source array

target - the target array

Returns:

the target array or a new one if the target array was too small

newBytes

public static byte[] newBytes(int len)

Create an array of bytes with the given size. If this is not possible because not enough memory is available, an OutOfMemoryError with the requested size in the message is thrown.

This method should be used if the size of the array is user defined, or stored in a file, so wrong size data can be distinguished from regular out-of-memory.

Parameters:

len - the number of bytes requested

Returns:

the byte array

Throws:

java.lang.OutOfMemoryError - if the allocation was too large

copyBytes

public static byte[] copyBytes(byte[] bytes,
                               int len)

Creates a copy of array of bytes with the new size. If this is not possible because not enough memory is available, an OutOfMemoryError with the requested size in the message is thrown.

This method should be used if the size of the array is user defined, or stored in a file, so wrong size data can be distinguished from regular out-of-memory.

Parameters:

bytes - source array

len - the number of bytes in the new array

Returns:

the byte array

Throws:

java.lang.OutOfMemoryError - if the allocation was too large

See Also:

Arrays.copyOf(byte[], int)

cloneByteArray

public static byte[] cloneByteArray(byte[] b)

Create a new byte array and copy all the data. If the size of the byte array is zero, the same array is returned.

Parameters:

b - the byte array (may not be null)

Returns:

a new byte array

getMemoryUsed

public static long getMemoryUsed()

Get the used memory in KB. This method possibly calls System.gc().

Returns:

the used memory

getMemoryFree

public static long getMemoryFree()

Get the free memory in KB. This method possibly calls System.gc().

Returns:

the free memory

getMemoryMax

public static long getMemoryMax()

Get the maximum memory in KB.

Returns:

the maximum memory

getGarbageCollectionTime

public static long getGarbageCollectionTime()

getGarbageCollectionCount

public static long getGarbageCollectionCount()

collectGarbage

public static void collectGarbage()

Run Java memory garbage collection.

newSmallArrayList

public static <T> java.util.ArrayList<T> newSmallArrayList()

Create a new ArrayList with an initial capacity of 4.

Type Parameters:

T - the type

Returns:

the object

sortTopN

public static <X> void sortTopN(X[] array,
                                int fromInclusive,
                                int toExclusive,
                                java.util.Comparator<? super X> comp)

Find the top limit values using given comparator and place them as in a full array sort, in descending order.

Type Parameters:

X - the type of elements

Parameters:

array - the array.

fromInclusive - the start index, inclusive

toExclusive - the end index, exclusive

comp - the comparator.

getResource

public static byte[] getResource(java.lang.String name)
                          throws java.io.IOException

Get a resource from the resource map.

Parameters:

name - the name of the resource

Returns:

the resource data

Throws:

java.io.IOException - on failure

callStaticMethod

public static java.lang.Object callStaticMethod(java.lang.String classAndMethod,
                                                java.lang.Object... params)
                                         throws java.lang.Exception

Calls a static method via reflection. This will try to use the method where the most parameter classes match exactly (this algorithm is simpler than the one in the Java specification, but works well for most cases).

Parameters:

classAndMethod - a string with the entire class and method name, eg. "java.lang.System.gc"

params - the method parameters

Returns:

the return value from this call

Throws:

java.lang.Exception - on failure

callMethod

public static java.lang.Object callMethod(java.lang.Object instance,
                                          java.lang.String methodName,
                                          java.lang.Object... params)
                                   throws java.lang.Exception

Calls an instance method via reflection. This will try to use the method where the most parameter classes match exactly (this algorithm is simpler than the one in the Java specification, but works well for most cases).

Parameters:

instance - the instance on which the call is done

methodName - a string with the method name

params - the method parameters

Returns:

the return value from this call

Throws:

java.lang.Exception - on failure

newInstance

public static java.lang.Object newInstance(java.lang.String className,
                                           java.lang.Object... params)
                                    throws java.lang.Exception

Creates a new instance. This will try to use the constructor where the most parameter classes match exactly (this algorithm is simpler than the one in the Java specification, but works well for most cases).

Parameters:

className - a string with the entire class, eg. "java.lang.Integer"

params - the constructor parameters

Returns:

the newly created object

Throws:

java.lang.Exception - on failure

getNonPrimitiveClass

public static java.lang.Class<?> getNonPrimitiveClass(java.lang.Class<?> clazz)

Convert primitive class names to java.lang.* class names.

Parameters:

clazz - the class (for example: int)

Returns:

the non-primitive class (for example: java.lang.Integer)

parseBoolean

public static boolean parseBoolean(java.lang.String value,
                                   boolean defaultValue,
                                   boolean throwException)

Parses the specified string to boolean value.

Parameters:

value - string to parse

defaultValue - value to return if value is null or on parsing error

throwException - throw exception on parsing error or return default value instead

Returns:

parsed or default value

Throws:

java.lang.IllegalArgumentException - on parsing error if throwException is true

getProperty

public static java.lang.String getProperty(java.lang.String key,
                                           java.lang.String defaultValue)

Get the system property. If the system property is not set, or if a security exception occurs, the default value is returned.

Parameters:

key - the key

defaultValue - the default value

Returns:

the value

getProperty

public static int getProperty(java.lang.String key,
                              int defaultValue)

Get the system property. If the system property is not set, or if a security exception occurs, the default value is returned.

Parameters:

key - the key

defaultValue - the default value

Returns:

the value

getProperty

public static boolean getProperty(java.lang.String key,
                                  boolean defaultValue)

Get the system property. If the system property is not set, or if a security exception occurs, the default value is returned.

Parameters:

key - the key

defaultValue - the default value

Returns:

the value

scaleForAvailableMemory

public static int scaleForAvailableMemory(int value)

Scale the value with the available memory. If 1 GB of RAM is available, the value is returned, if 2 GB are available, then twice the value, and so on.

Parameters:

value - the value to scale

Returns:

the scaled value

currentNanoTime

public static long currentNanoTime()

Returns the current value of the high-resolution time source.

Returns:

time in nanoseconds, never equal to 0

See Also:

System.nanoTime()

currentNanoTimePlusMillis

public static long currentNanoTimePlusMillis(int ms)

Returns the current value of the high-resolution time source plus the specified offset.

Parameters:

ms - additional offset in milliseconds

Returns:

time in nanoseconds, never equal to 0

See Also:

System.nanoTime()

nanoTimePlusMillis

public static long nanoTimePlusMillis(long nanoTime,
                                      int ms)

Returns the current value of the high-resolution time source plus the specified offset.

Parameters:

nanoTime - time in nanoseconds

ms - additional offset in milliseconds

Returns:

time in nanoseconds, never equal to 0

See Also:

System.nanoTime()

createSingleThreadExecutor

public static java.util.concurrent.ThreadPoolExecutor createSingleThreadExecutor(java.lang.String threadName)

createSingleThreadExecutor

public static java.util.concurrent.ThreadPoolExecutor createSingleThreadExecutor(java.lang.String threadName,
                                                                                 java.util.concurrent.BlockingQueue<java.lang.Runnable> workQueue)

flushExecutor

public static void flushExecutor(java.util.concurrent.ThreadPoolExecutor executor)

Makes sure that all currently submitted tasks are processed before this method returns. It is assumed that there will be no new submissions to this executor, once this method has started. It is assumed that executor is single-threaded, and flush is done by submitting a dummy task and waiting for its completion.

Parameters:

executor - to flush

shutdownExecutor

public static void shutdownExecutor(java.util.concurrent.ThreadPoolExecutor executor)