Utils (H2 Database Engine 2.0.0 API)

java.lang.Object
- org.h2.util.Utils

```
public class Utils
extends Object
```
This utility class contains miscellaneous functions.

嵌套类概要

嵌套类
限定符和类型	类和说明
`static interface`	`Utils.ClassFactory` The utility methods will try to use the provided class factories to convert binary name of class to Class object.

字段概要

字段
限定符和类型字段和说明

static byte[] EMPTY_BYTES
An 0-size byte array.

static int[] EMPTY_INT_ARRAY
An 0-size int array.

字段
限定符和类型	字段和说明
`static byte[]`	`EMPTY_BYTES` An 0-size byte array.
`static int[]`	`EMPTY_INT_ARRAY` An 0-size int array.

方法概要

所有方法静态方法具体方法
限定符和类型	方法和说明
`static Object`	`callMethod(Object instance, String methodName, Object... params)` Calls an instance method via reflection.
`static Object`	`callStaticMethod(String classAndMethod, 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 ThreadPoolExecutor`	`createSingleThreadExecutor(String threadName)`
`static ThreadPoolExecutor`	`createSingleThreadExecutor(String threadName, BlockingQueue<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(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 Class<?>`	`getNonPrimitiveClass(Class<?> clazz)` Convert primitive class names to java.lang.* class names.
`static boolean`	`getProperty(String key, boolean defaultValue)` Get the system property.
`static int`	`getProperty(String key, int defaultValue)` Get the system property.
`static String`	`getProperty(String key, String defaultValue)` Get the system property.
`static byte[]`	`getResource(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 Object`	`newInstance(String className, Object... params)` Creates a new instance.
`static <T> ArrayList<T>`	`newSmallArrayList()` Create a new ArrayList with an initial capacity of 4.
`static boolean`	`parseBoolean(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(ThreadPoolExecutor executor)`
`static <X> void`	`sortTopN(X[] array, int fromInclusive, int toExclusive, Comparator<? super X> comp)` Find the top limit values using given comparator and place them as in a full array sort, in descending order.

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 字段详细资料
  - 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.
- 方法详细资料
  - 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.
    
    参数:
    
    bytes - the byte array
    
    pattern - the pattern
    
    start - the start index from where to search
    
    返回:
    
    the index
  - getByteArrayHash
```
public static int getByteArrayHash(byte[] value)
```
    Calculate the hash code of the given byte array.
    
    参数:
    
    value - the byte array
    
    返回:
    
    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.
    
    参数:
    
    test - the first array
    
    good - the second array
    
    返回:
    
    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.
    
    参数:
    
    source - the source array
    
    target - the target array
    
    返回:
    
    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.
    
    参数:
    
    len - the number of bytes requested
    
    返回:
    
    the byte array
    
    抛出:
    
    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.
    
    参数:
    
    bytes - source array
    
    len - the number of bytes in the new array
    
    返回:
    
    the byte array
    
    抛出:
    
    OutOfMemoryError - if the allocation was too large
    
    另请参阅:
    
    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.
    
    参数:
    
    b - the byte array (may not be null)
    
    返回:
    
    a new byte array
  - getMemoryUsed
```
public static long getMemoryUsed()
```
    Get the used memory in KB. This method possibly calls System.gc().
    
    返回:
    
    the used memory
  - getMemoryFree
```
public static long getMemoryFree()
```
    Get the free memory in KB. This method possibly calls System.gc().
    
    返回:
    
    the free memory
  - getMemoryMax
```
public static long getMemoryMax()
```
    Get the maximum memory in KB.
    
    返回:
    
    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> ArrayList<T> newSmallArrayList()
```
    Create a new ArrayList with an initial capacity of 4.
    
    类型参数:
    
    T - the type
    
    返回:
    
    the object
  - sortTopN
```
public static <X> void sortTopN(X[] array,
                                int fromInclusive,
                                int toExclusive,
                                Comparator<? super X> comp)
```
    Find the top limit values using given comparator and place them as in a full array sort, in descending order.
    
    类型参数:
    
    X - the type of elements
    
    参数:
    
    array - the array.
    
    fromInclusive - the start index, inclusive
    
    toExclusive - the end index, exclusive
    
    comp - the comparator.
  - getResource
```
public static byte[] getResource(String name)
                          throws IOException
```
    Get a resource from the resource map.
    
    参数:
    
    name - the name of the resource
    
    返回:
    
    the resource data
    
    抛出:
    
    IOException - on failure
  - callStaticMethod
```
public static Object callStaticMethod(String classAndMethod,
                                      Object... params)
                               throws 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).
    
    参数:
    
    classAndMethod - a string with the entire class and method name, eg. "java.lang.System.gc"
    
    params - the method parameters
    
    返回:
    
    the return value from this call
    
    抛出:
    
    Exception - on failure
  - callMethod
```
public static Object callMethod(Object instance,
                                String methodName,
                                Object... params)
                         throws 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).
    
    参数:
    
    instance - the instance on which the call is done
    
    methodName - a string with the method name
    
    params - the method parameters
    
    返回:
    
    the return value from this call
    
    抛出:
    
    Exception - on failure
  - newInstance
```
public static Object newInstance(String className,
                                 Object... params)
                          throws 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).
    
    参数:
    
    className - a string with the entire class, eg. "java.lang.Integer"
    
    params - the constructor parameters
    
    返回:
    
    the newly created object
    
    抛出:
    
    Exception - on failure
  - getNonPrimitiveClass
```
public static Class<?> getNonPrimitiveClass(Class<?> clazz)
```
    Convert primitive class names to java.lang.* class names.
    
    参数:
    
    clazz - the class (for example: int)
    
    返回:
    
    the non-primitive class (for example: java.lang.Integer)
  - parseBoolean
```
public static boolean parseBoolean(String value,
                                   boolean defaultValue,
                                   boolean throwException)
```
    Parses the specified string to boolean value.
    
    参数:
    
    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
    
    返回:
    
    parsed or default value
    
    抛出:
    
    IllegalArgumentException - on parsing error if throwException is true
  - getProperty
```
public static String getProperty(String key,
                                 String defaultValue)
```
    Get the system property. If the system property is not set, or if a security exception occurs, the default value is returned.
    
    参数:
    
    key - the key
    
    defaultValue - the default value
    
    返回:
    
    the value
  - getProperty
```
public static int getProperty(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.
    
    参数:
    
    key - the key
    
    defaultValue - the default value
    
    返回:
    
    the value
  - getProperty
```
public static boolean getProperty(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.
    
    参数:
    
    key - the key
    
    defaultValue - the default value
    
    返回:
    
    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.
    
    参数:
    
    value - the value to scale
    
    返回:
    
    the scaled value
  - currentNanoTime
```
public static long currentNanoTime()
```
    Returns the current value of the high-resolution time source.
    
    返回:
    
    time in nanoseconds, never equal to 0
    
    另请参阅:
    
    System.nanoTime()
  - currentNanoTimePlusMillis
```
public static long currentNanoTimePlusMillis(int ms)
```
    Returns the current value of the high-resolution time source plus the specified offset.
    
    参数:
    
    ms - additional offset in milliseconds
    
    返回:
    
    time in nanoseconds, never equal to 0
    
    另请参阅:
    
    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.
    
    参数:
    
    nanoTime - time in nanoseconds
    
    ms - additional offset in milliseconds
    
    返回:
    
    time in nanoseconds, never equal to 0
    
    另请参阅:
    
    System.nanoTime()
  - createSingleThreadExecutor
```
public static ThreadPoolExecutor createSingleThreadExecutor(String threadName)
```
  - createSingleThreadExecutor
```
public static ThreadPoolExecutor createSingleThreadExecutor(String threadName,
                                                            BlockingQueue<Runnable> workQueue)
```
  - flushExecutor
```
public static void flushExecutor(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 it's completion.
    
    参数:
    
    executor - to flush
  - shutdownExecutor
```
public static void shutdownExecutor(ThreadPoolExecutor executor)
```

类 Utils

嵌套类概要

字段概要

方法概要

从类继承的方法 java.lang.Object

字段详细资料

EMPTY_BYTES

EMPTY_INT_ARRAY

方法详细资料

indexOf

getByteArrayHash

compareSecure

copy

newBytes

copyBytes

cloneByteArray

getMemoryUsed

getMemoryFree

getMemoryMax

getGarbageCollectionTime

getGarbageCollectionCount

collectGarbage

newSmallArrayList

sortTopN

getResource

callStaticMethod

callMethod

newInstance

getNonPrimitiveClass

parseBoolean

getProperty

getProperty

getProperty

scaleForAvailableMemory

currentNanoTime

currentNanoTimePlusMillis

nanoTimePlusMillis

createSingleThreadExecutor

createSingleThreadExecutor

flushExecutor

shutdownExecutor