概述

我们以xyz文件格式为例，来说明文件编解码的代码设计。xyz文件格式内容如下：

• header部分：文件头，包含文件版本号、文件类型、文件大小等信息
• body部分：文件主体

通用设计大概如下

classDiagram
    class XyzHeader {
        + byte[] content
    }
    class XyzBody {
        + byte[] content
    }
    class Xyz{
        + XyzHeader header
        + XyzBody body
    }
    class XyzReader {
        + Xyz read(fileName: string)
        + void process(String fileName, XyzProcessor processor)
        - XyzHeader readHeader()
        - XyzBody readBody()
    }
    class XyzProcessor {
        <<interface>>
        + void processHeader(XyzHeader header)
        + void processBody(XyzBody body)
    }
    class XyzReadCollectProcessor {
        Xyz getXyz()
    }
    Xyz --> XyzHeader: contains
    Xyz --> XyzBody: contains
    XyzReader --> Xyz: reads
    XyzReader --> XyzProcessor: processes
    XyzReadCollectProcessor --|> XyzProcessor: implements

Java

使用java.io.RandomAccessFile和java.nio.channels.FileChannel来实现文件读取，使用io.netty.buffer.ByteBuf来读写文件。

核心代码举例:

XyzReader:

public class XyzHeader {
    private byte[] content;
}
public class XyzBody {
    private byte[] content;
}
public class Xyz {
    private XyzHeader header;
    private XyzBody body;
}
public interface XyzProcessor {
    void processHeader(XyzHeader header);
    void processBody(XyzBody body);
}
public class XyzReadCollectProcessor implements XyzProcessor {
    private final Xyz xyz = new Xyz();
    public Xyz getXyz() {
        return xyz;
    }
}
public class XyzReader {
    public Xyz read(String fileName) throws Exception {
    }

    private XyzHeader readHeader(FileChannel fileChannel) throws Exception {
    }

    private XyzBody readBody(FileChannel fileChannel) throws Exception {
    }
}