操作系统在allocateDirect()方法执行时会分配一块直接内存,这部分内存java代码和系统都可以进行访问。...i = 0; try { while (true) { ByteBuffer byteBuffer = ByteBuffer.allocateDirect...(DirectByteBuffer.java:123) at java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:311) at cn.itcast.jvm.t1...allocateDirect()中返回一个DirectByteBuffer对象。...public static ByteBuffer allocateDirect(int capacity) { return new DirectByteBuffer(capacity);
前言 写NIO程序时,经常使用ByteBuffer来读取写入数据,那使用ByteBuffer.allocate()还是ByteBuffer.allocateDirect分配呢?...测试 分配-Xmx=100m,没有设置-XX:MaxDirectMemorySize,默认大小和-Xmx大小相同 //分配128MB直接内存 ByteBuffer bb = ByteBuffer.allocateDirect...static void main(String[] args) throws InterruptedException{ //分配512MB直接缓存 ByteBuffer bb = ByteBuffer.allocateDirect
count = 0; try { while (true){ ByteBuffer byteBuffer = ByteBuffer.allocateDirect...(DirectByteBuffer.java:123) at java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:311) at com.memory.BufferTest2
A direct byte buffer may be created by invoking the allocateDirect factory method of this class....文档中也说了,直接内存使用allocateDirect创建,但是它比申请普通的堆内存需要耗费更高的性能。不过,这部分的数据是在JVM之外的,因此它不会占用应用的内存。...)-begin.getTime()); begin = new Date(); for(int i=0;i<time;i++){ ByteBuffer buffer = ByteBuffer.allocateDirect...System.out.println(end.getTime()-begin.getTime()); begin = new Date(); ByteBuffer buffer2 = ByteBuffer.allocateDirect
public static void main(String[] args){ //直接分配本地内存空间 ByteBuffer byteBuffer = ByteBuffer.allocateDirect...outChannel = new FileOutputStream(dest).getChannel(); ByteBuffer byteBuffer = ByteBuffer.allocateDirect...= System.currentTimeMillis(); return end - start; } } ---- 深入 ByteBuffer 源码 ByteBuffer.allocateDirect...() 方法 public static ByteBuffer allocateDirect(int capacity) { return new DirectByteBuffer(capacity...count = 0; try { while(true){ ByteBuffer byteBuffer = ByteBuffer.allocateDirect
MaxDirectMemorySize=60M */ @Test public void testGetMaxDirectMemory(){ ByteBuffer.allocateDirect...MaxDirectMemorySize=60M */ @Test public void testGetDirectMemoryUsage(){ ByteBuffer.allocateDirect...(DirectByteBuffer.java:118) at java.base/java.nio.ByteBuffer.allocateDirect(ByteBuffer.java...:317) 如果上面的ByteBuffer.allocateDirect改为分配超过60M,则运行抛出OutOfMemoryError 使用NMT查看directBuffer使用情况 jcmd 3088...使用的值一致,改变ByteBuffer.allocateDirect的值再重新查看,可以发现Other部分跟着改变;因而初步断定Other部分应该是可以反映direct memory的使用大小 小结 -
读写数据 在直接内存中,通过allocateDirect(int byte_length)申请直接内存。这段内存可以理解为一段普通的基于Byte的数组,因此插入和读取都跟普通的数组差不多。...举个例子: ByteBuffer buffer = ByteBuffer.allocateDirect(1024); buffer.putChar('a'); System.out.println(buffer...final Buffer rewind() { position = 0; mark = -1; return this; } 使用案例 ByteBuffer buffer = ByteBuffer.allocateDirect...注意每次写入数据的时候,position都会自动加上写入数据的长度,指向下一个该写入的起始位置: 下面看看如何写入一段byte[]或者字符串: ByteBuffer buffer = ByteBuffer.allocateDirect...ByteBuffer buffer = ByteBuffer.allocateDirect(10); buffer.put(new byte[]{1,2,3,4}); System.out.println
ByteBufferTest { public static void main(String[] args) { ByteBuffer byteBuffer = ByteBuffer.allocateDirect...count = 0; try { while (true){ ByteBuffer byteBuffer = ByteBuffer.allocateDirect...(DirectByteBuffer.java:123) at java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:311) at com.memory.BufferTest2
注解@1 底层调用ByteBuffer#allocateDirect来分配堆外内存,具体为直接new DirectByteBuffer() public static ByteBuffer allocateDirect...注解@1 堆外内存分配同InstrumentedUnpooledUnsafeDirectByteBuf,通过父类UnpooledDirectByteBuf#allocateDirect调用ByteBuffer...#allocateDirect来分配堆外内存,堆内存直接new DirectByteBuffer public static ByteBuffer allocateDirect(int capacity
buf = ByteBuffer.allocate(48); 分配一个可存储1024个字符的CharBuffer: CharBuffer buf = CharBuffer.allocate(1024); allocateDirect...使用allocateDirect可一次性分配capacity大小的连续字节空间。...通过allocateDirect方法来创建具有连续空间的ByteBuffer对象虽然可以在一定程度上提高效率,但这种方式并不是平台独立的。...而且allocateDirect方法需要较长的时间来分配内存空间,在释放空间时也较慢。因此,慎用allocateDirect。
allocateDirect创建直接缓冲区 public static ByteBuffer allocateDirect(int capacity) { return new DirectByteBuffer...System.currentTimeMillis()-start)); start = System.currentTimeMillis(); ByteBuffer buffer2 = ByteBuffer.allocateDirect...System.currentTimeMillis(); for (int i = 0; i < time; i++) { ByteBuffer buffer = ByteBuffer.allocateDirect
对Nio的ByteBuffer进行了封装,通过ByteBuffer的allocateDirect方法实现缓存的申请。...ByteBuffer initialBuffer, int maxCapacity) { //判断逻辑已经忽略 this.alloc = alloc; setByteBuffer(allocateDirect...(initialCapacity)); } protected ByteBuffer allocateDirect(int initialCapacity) { return ByteBuffer.allocateDirect
."); ByteBuffer buf = ByteBuffer.allocateDirect(_1MB); // 将引用加入集合中防止被...(DirectByteBuffer.java:123) at java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:306) at test.oom.DirectMemoryOOM.main
audio_buffer_size = (audio_buffer_size+0xf) & (~0xf); audio_buffer_ = ByteBuffer.allocateDirect...param_info_size = (param_info_size+0xf) & (~0xf); parameter_info_ = ByteBuffer.allocateDirect...video_buffer_size = (video_buffer_size+0xf) & (~0xf); video_buffer_ = ByteBuffer.allocateDirect
先来看一个 Demo:在 Demo 中分配堆外内存用的是 allocateDirect 方法,但其内部调用的是 DirectByteBuffer,换言之,DirectByteBuffer 才是实际操作堆外内存的类...Demo { public static void main( String[] args ) { //分配一块1024Bytes的堆外内存(直接内存) //allocateDirect...方法内部调用的是DirectByteBuffer ByteBuffer buffer=ByteBuffer.allocateDirect(1024); System.out.println
FileChannel channel = file.getChannel(); ByteBuffer byteBuffer = ByteBuffer.allocateDirect...startTime = System.currentTimeMillis(); ByteBuffer byteBuffer = ByteBuffer.allocateDirect
limit <= capacity * * 四、直接缓冲区与非直接缓冲区: * 非直接缓冲区:通过 allocate() 方法分配缓冲区,将缓冲区建立在 JVM 的内存中 * 直接缓冲区:通过 allocateDirect...buf.get()); } } 四、直接缓冲区与非直接缓冲区: 非直接缓冲区:通过 allocate() 方法分配缓冲区,将缓冲区建立在 JVM 的内存中 直接缓冲区:通过 allocateDirect...不想在内存中开辟空间采用这种方式 @Test public void test3(){ // 分配直接缓冲区 ByteBuffer buf = ByteBuffer.allocateDirect
直接缓冲区 只有ByteBuffer可以获得直接缓冲区,通过allocateDirect()获取的缓冲区为直接缓冲区,这些缓冲区是建立在物理内存之中的。...public static ByteBuffer allocateDirect(int capacity) { return new DirectByteBuffer(capacity); }
直接ByteBuffer是通过调用ByteBuffer.allocateDirect()函数产生的,注意用一个wrap()函数所创建的被包装的缓冲区总是非直接的。...partial API listing public static ByteBuffer allocate(int capacity) public static ByteBuffer allocateDirect
如何使用DirectByteBuffer 如果需要实例化一个DirectByteBuffer,可以使用java.nio.ByteBuffer#allocateDirect这个方法: public static...ByteBuffer allocateDirect(int capacity) { return new DirectByteBuffer(capacity);} DirectByteBuffer...读写数据 在直接内存中,通过allocateDirect(int byte_length)申请直接内存。这段内存可以理解为一段普通的基于Byte的数组,因此插入和读取都跟普通的数组差不多。...举个例子: ByteBuffer buffer = ByteBuffer.allocateDirect(1024); buffer.putChar('a');System.out.println(buffer...ByteBuffer buffer = ByteBuffer.allocateDirect(10); buffer.put(new byte[]{1,2,3,4});System.out.println
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