Java读写二进制文件示例

import java.io.DataInput;import java.io.DataOutput;import java.io.DataOutputStream;import java.io.FileOutputStream;import java.io.RandomAccessFile;import java.util.ArrayList;import java.util.List;class Employee{ public static int RecordSize=72;// 总计8+30*2+4=72字节，算准总字节数对于连续读取很重要 private long id;// long类型似占8字节 private String name; public static int NameSize=30;// 预计名称最多30个字符，占30*2=60字节 private int age;// int类型占4字节 public Employee(long id,String name,int age){ this.id=id; this.name=name; this.age=age; } public String toString(){ return "ID="+id+" name:"+name+" age:"+age; } public long getId() { return id; } public void setId(long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; }}public class Test3{ public static void main(String[] args) throws Exception{ // 准备数据 List<Employee> ls=new ArrayList<Employee>(); final int AMOUT=10; for(long i=0;i<AMOUT;i++){ ls.add(new Employee(i,"克隆人-"+i,(int)(i %100))); } // 写入 DataOutputStream out=new DataOutputStream(new FileOutputStream("C:\\Users\\IBM_ADMIN\\Desktop\\emp.dat")); for(Employee emp:ls){ writeEmp(out,emp); } // 挨个读取 RandomAccessFile in=new RandomAccessFile("C:\\Users\\IBM_ADMIN\\Desktop\\emp.dat","r"); int len=(int)(in.length()/Employee.RecordSize); for(long i=0;i<len;i++){ in.seek(i*Employee.RecordSize); Employee emp=readEmp(in); System.out.println(emp.toString()); } } private static void writeEmp(DataOutput out,Employee emp) throws Exception{ writeString(emp.getName(),Employee.NameSize,out); out.writeLong(emp.getId()); out.writeInt(emp.getAge()); } private static Employee readEmp(DataInput in) throws Exception{ String name=readString(Employee.NameSize,in); long sn=in.readLong(); int age=in.readInt(); return new Employee(sn,name,age); } // 写入最大长度为size的字符串，不足写0 private static void writeString(String str,int size,DataOutput out) throws Exception{ for(int i=0;i<size;i++){ char c=0; if(i<str.length()){ c=str.charAt(i); } out.writeChar(c); } } // 读入最大长度为size的字符串 private static String readString(int size,DataInput in) throws Exception{ StringBuilder sb=new StringBuilder(); for(int i=0;i<size;i++){ char c=in.readChar(); if(c==0){ continue; }else{ sb.append(c); } } return sb.toString(); }}

ID=0 name:克隆人-0 age:0ID=1 name:克隆人-1 age:1ID=2 name:克隆人-2 age:2ID=3 name:克隆人-3 age:3ID=4 name:克隆人-4 age:4ID=5 name:克隆人-5 age:5ID=6 name:克隆人-6 age:6ID=7 name:克隆人-7 age:7ID=8 name:克隆人-8 age:8ID=9 name:克隆人-9 age:9