JavaIO性能优化 - CSDN文库

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41

CHAPTER 4

I/O Performance

B

OTH

client and server programs often use the java.io package. While this

package is designed with ease of use in mind, developers new to the platform

often make mistakes that can lead to poor I/O performance. Fortunately, a better

understanding of this package can lead to major improvements in I/O

performance.

Section 4.1 provides a brief overview of the

java.io package, identifies the

most common cause of poor I/O performance, and describes several different

approaches to solving this problem. Section 4.2 focuses on object serialization, a

key part of many of the newest features in the Java platform.

4.1 Basic I/O

Two abstract classes shape the architecture of the java.io package: InputStream

and OutputStream. These interfaces define the key abstractions for I/O opera-

tions. Concrete implementations of

InputStream and OutputStream provide

access to different types of data sources such as disks and network connections.

The

java.io package also provides several filter streams that don’t point to a

specific data source and are meant to be stacked on top of other streams. These

filter streams are at the heart of the

java.io architecture. From a performance

perspective, the most interesting filter streams are buffered streams. Figure 4-1

shows a simplified class hierarchy that includes the buffered streams.

4.1.1 Buffered Streams

The leading cause of poor I/O performance is failing to buffer I/O operations.

Hard disks are very good at reading and writing sizable chunks of data, but they

are much less efficient when working with small blocks of data. To maximize I/O

performance, you should batch read and write operations. This is exactly what

buffered streams are designed for.

By default, most of the streams provided in the Java libraries write one byte of

data at a time. Instead of putting buffering behavior into each individual stream

JPIOPerformance.fm Page 41 Monday, May 1, 2000 7:39 PM

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