我正在学习Java中的套接字编程。我见过客户端/服务器应用示例，其中一些使用DataOutputStream，有些使用ObjectOutputStream。
两者有什么区别？
是否存在性能差异？
答案 0 :(得分：23)
DataInput / OutputStream通常执行得更好，因为它更简单。它只能读/写原始类型和字符串。
ObjectInput / OutputStream可以读/写任何对象类型以及原语。如果您想发送复杂数据，效率会降低，但更容易使用。
我认为在您知道其性能是个问题之前，Object * Stream是最佳选择。
答案 1 :(得分：6)
DataOutputStream和ObjectOutputStream：处理基本类型时，除了ObjectOutputStream创建的标题之外没有区别。
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。
答案 2 :(得分：5)
这可能对几年后仍在寻找答案的人有用...根据我对最近的JVM（1.8_51）的测试，ObjectOutput/InputStream的速度几乎是DataOutput/InputStream的2倍。用于读/写大量的双倍！
以下是编写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在上次Java版本中对JVM进行了大量优化以使用ObjectStream，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。
所以看起来今天没有太多理由可以使用DataStream了。 ＆＃34;不要试图超越JVM＆＃34;，只需使用最直接的方式，即ObjectStream s：）
以下是测试代码：
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");
});
}
答案 3 :(得分：-1)
只有实现java.io.Serializable接口的对象才能使用ObjectOutputStream写入流。原始数据类型也可以使用DataOutput中的相应方法写入流。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。