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[英]difference between “DataOutputStream” and “ObjectOutputStream”
[英]What's the difference between DataOutputStream and ObjectOutputStream?
我正在学习Java中的套接字编程。 我见过客户端/服务器应用程序示例,有些使用DataOutputStream
,有些使用ObjectOutputStream
。
这两者有什么区别?
有性能差异吗?
DataInput / OutputStream通常执行得更好,因为它更简单。 它只能读/写初始类型和字符串。
ObjectInput / OutputStream可以读/写任何对象类型以及原语。 如果要发送复杂数据,效率会降低,但更容易使用。
我会假设Object * Stream是最好的选择,直到你知道它的性能是一个问题。
DataOutputStream
和ObjectOutputStream
:处理基本类型时,除了ObjectOutputStream
创建的头之外没有区别。
使用ObjectOutputStream
类,可以将实现Serializable
的类的实例写入输出流,并可以使用ObjectInputStream
进行回读。
DataOutputStream
只能处理基本类型。
这可能对几年后仍在寻找答案的人有用...根据我在最近的JVM(1.8_51)上的测试, ObjectOutput/InputStream
比DataOutput/InputStream
快几乎是读取/写入大数组的2倍快双倍!
下面是写入1000万个项目数组的结果(100万个结果基本相同)。 为了完整起见,我还包括文本格式(BufferedWriter / Reader):
TestObjectStream written 10000000 items, took: 409ms, or 24449.8778 items/ms, filesize 80390629b
TestDataStream written 10000000 items, took: 727ms, or 13755.1582 items/ms, filesize 80000000b
TestBufferedWriter written 10000000 items, took: 13700ms, or 729.9270 items/ms, filesize 224486395b
读:
TestObjectStream read 10000000 items, took: 250ms, or 40000.0000 items/ms, filesize 80390629b
TestDataStream read 10000000 items, took: 424ms, or 23584.9057 items/ms, filesize 80000000b
TestBufferedWriter read 10000000 items, took: 6298ms, or 1587.8057 items/ms, filesize 224486395b
我相信Oracle在上一次Java版本中对使用ObjectStream
的JVM进行了大量优化,因为这是编写/读取数据(包括序列化)的最常用方式,因此位于Java性能关键路径上。
所以看起来今天没有太多理由再使用DataStream
。 “不要试图超越JVM”,只需使用最直接的方式,即ObjectStream
s :)
这是测试的代码:
class Generator {
private int seed = 1235436537;
double generate(int i) {
seed = (seed + 1235436537) % 936855463;
return seed / (i + 1.) / 524323.;
}
}
class Data {
public final double[] array;
public Data(final double[] array) {
this.array = array;
}
}
class TestObjectStream {
public void write(File dest, Data data) {
try (ObjectOutputStream out = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(dest)))) {
for (int i = 0; i < data.array.length; i++) {
out.writeDouble(data.array[i]);
}
} catch (IOException e) {
throw new RuntimeIoException(e);
}
}
public void read(File dest, Data data) {
try (ObjectInputStream in = new ObjectInputStream(new BufferedInputStream(new FileInputStream(dest)))) {
for (int i = 0; i < data.array.length; i++) {
data.array[i] = in.readDouble();
}
} catch (IOException e) {
throw new RuntimeIoException(e);
}
}
}
class TestDataStream {
public void write(File dest, Data data) {
try (DataOutputStream out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(dest)))) {
for (int i = 0; i < data.array.length; i++) {
out.writeDouble(data.array[i]);
}
} catch (IOException e) {
throw new RuntimeIoException(e);
}
}
public void read(File dest, Data data) {
try (DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream(dest)))) {
for (int i = 0; i < data.array.length; i++) {
data.array[i] = in.readDouble();
}
} catch (IOException e) {
throw new RuntimeIoException(e);
}
}
}
class TestBufferedWriter {
public void write(File dest, Data data) {
try (BufferedWriter out = new BufferedWriter(new FileWriter(dest))) {
for (int i = 0; i < data.array.length; i++) {
out.write(Double.toString(data.array[i]));
out.newLine();
}
} catch (IOException e) {
throw new RuntimeIoException(e);
}
}
public void read(File dest, Data data) {
try (BufferedReader in = new BufferedReader(new FileReader(dest))) {
String line = in.readLine();
int i = 0;
while (line != null) {
if(!line.isEmpty()) {
data.array[i++] = Double.parseDouble(line);
}
line = in.readLine();
}
} catch (IOException e) {
throw new RuntimeIoException(e);
}
}
}
@Test
public void testWrite() throws Exception {
int N = 10000000;
double[] array = new double[N];
Generator gen = new Generator();
for (int i = 0; i < array.length; i++) {
array[i] = gen.generate(i);
}
Data data = new Data(array);
Map<Class, BiConsumer<File, Data>> subjects = new LinkedHashMap<>();
subjects.put(TestDataStream.class, new TestDataStream()::write);
subjects.put(TestObjectStream.class, new TestObjectStream()::write);
subjects.put(TestBufferedWriter.class, new TestBufferedWriter()::write);
subjects.forEach((aClass, fileDataBiConsumer) -> {
File f = new File("test." + aClass.getName());
long start = System.nanoTime();
fileDataBiConsumer.accept(f, data);
long took = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
System.out.println(aClass.getSimpleName() + " written " + N + " items, took: " + took + "ms, or " + String.format("%.4f", (N / (double)took)) + " items/ms, filesize " + f.length() + "b");
});
}
@Test
public void testRead() throws Exception {
int N = 10000000;
double[] array = new double[N];
Data data = new Data(array);
Map<Class, BiConsumer<File, Data>> subjects = new LinkedHashMap<>();
subjects.put(TestDataStream.class, new TestDataStream()::read);
subjects.put(TestObjectStream.class, new TestObjectStream()::read);
subjects.put(TestBufferedWriter.class, new TestBufferedWriter()::read);
subjects.forEach((aClass, fileDataBiConsumer) -> {
File f = new File("test." + aClass.getName());
long start = System.nanoTime();
fileDataBiConsumer.accept(f, data);
long took = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
System.out.println(aClass.getSimpleName() + " read " + N + " items, took: " + took + "ms, or " + String.format("%.4f", (N / (double)took)) + " items/ms, filesize " + f.length() + "b");
});
}
只有使用ObjectOutputStream
才能将实现java.io.Serializable
接口的对象写入流。还可以使用DataOutput中的相应方法将预定义数据类型写入流中。 也可以使用writeUTF方法编写字符串。 但另一方面, DataInputStream
允许应用程序以可移植的方式将原始Java数据类型写入输出流。
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