缓冲流

// BufferedOutputStream 核心逻辑（简化版）
public class BufferedOutputStream extends FilterOutputStream {
    protected byte[] buf;          // 内部缓冲区
    protected int count;           // 当前已缓冲的字节数

    public synchronized void write(int b) throws IOException {
        if (count >= buf.length) {
            flushBuffer();  // 缓冲区满，批量写出到被装饰的流
        }
        buf[count++] = (byte) b;  // 只写到内部数组，不触发物理写入
    }

    public synchronized void flush() throws IOException {
        flushBuffer();     // 强制写出
        out.flush();       // 再flush底层流
    }

    private void flushBuffer() throws IOException {
        if (count > 0) {
            out.write(buf, 0, count);  // 一次性批量写出
            count = 0;
        }
    }
}

import java.io.*;
import java.util.ArrayList;
import java.util.List;

/**
 * 飞翔科技 - 日志分析工具
 * 使用 BufferedReader.readLine() 按行读取日志
 */
public class LogAnalyzer {
    public static void main(String[] args) {
        String logPath = "C:/feixiang/logs/system.log";
        List<String> errorLines = new ArrayList<>();
        int totalLines = 0;
        int errorCount = 0;
        int warnCount = 0;
        int infoCount = 0;

        try (BufferedReader br = new BufferedReader(
                new InputStreamReader(
                    new FileInputStream(logPath), "UTF-8"))) {

            String line;
            while ((line = br.readLine()) != null) {
                totalLines++;
                if (line.contains("[ERROR]")) {
                    errorCount++;
                    errorLines.add(line);
                } else if (line.contains("[WARN]")) {
                    warnCount++;
                } else if (line.contains("[INFO]")) {
                    infoCount++;
                }
            }

        } catch (IOException e) {
            System.err.println("日志分析失败：" + e.getMessage());
            return;
        }

        // 输出统计报告
        System.out.println("=== 飞翔科技系统日志分析报告 ===");
        System.out.println("日志文件路径：" + logPath);
        System.out.println("总行数：" + totalLines);
        System.out.println("--------------------------------");
        System.out.printf("INFO  : %d 条%n", infoCount);
        System.out.printf("WARN  : %d 条%n", warnCount);
        System.out.printf("ERROR : %d 条%n", errorCount);
        System.out.println("--------------------------------");

        if (!errorLines.isEmpty()) {
            System.out.println("\n错误日志详情：");
            for (int i = 0; i < errorLines.size(); i++) {
                System.out.printf("  #%d: %s%n", (i + 1), errorLines.get(i));
            }
        }
    }
}

import java.io.*;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;

/**
 * 飞翔科技 - 部门员工筛选工具
 * 使用 BufferedReader/BufferedWriter 高效处理CSV文件
 */
public class EmployeeFilter {

    static class Employee {
        String id;
        String name;
        String department;
        int age;

        Employee(String id, String name, String department, int age) {
            this.id = id;
            this.name = name;
            this.department = department;
            this.age = age;
        }

        String toCsv() {
            return String.join(",", id, name, department, String.valueOf(age));
        }
    }

    public static void main(String[] args) {
        String inputPath = "C:/feixiang/data/employees.csv";
        String outputPath = "C:/feixiang/data/tech_dept_employees.csv";

        List<Employee> techEmployees = new ArrayList<>();

        // 第一步：使用 BufferedReader 读取并筛选
        try (BufferedReader br = new BufferedReader(
                new InputStreamReader(
                    new FileInputStream(inputPath), StandardCharsets.UTF_8))) {

            // 读取并跳过表头
            String header = br.readLine();
            if (header == null) {
                System.err.println("CSV文件为空！");
                return;
            }

            String line;
            while ((line = br.readLine()) != null) {
                String[] parts = line.split(",");
                if (parts.length >= 4) {
                    String dept = parts[2].trim();
                    // 筛选技术部员工
                    if ("技术部".equals(dept) || "技术总监".equals(dept)) {
                        techEmployees.add(new Employee(
                            parts[0].trim(),
                            parts[1].trim(),
                            dept,
                            Integer.parseInt(parts[3].trim())
                        ));
                    }
                }
            }
        } catch (IOException e) {
            System.err.println("CSV读取失败：" + e.getMessage());
            return;
        }

        // 第二步：使用 BufferedWriter 写出筛选结果
        try (BufferedWriter bw = new BufferedWriter(
                new OutputStreamWriter(
                    new FileOutputStream(outputPath), StandardCharsets.UTF_8))) {

            // 写表头
            bw.write("员工ID,姓名,部门,年龄");
            bw.newLine();

            // 写数据行
            for (Employee emp : techEmployees) {
                bw.write(emp.toCsv());
                bw.newLine();
            }

            System.out.println("=== 筛选结果 ===");
            System.out.println("技术部员工共 " + techEmployees.size() + " 人");
            System.out.println("已输出到：" + outputPath);
            System.out.println("\n技术部员工列表：");
            for (Employee emp : techEmployees) {
                System.out.printf("  %s | %s | %s | %d岁%n",
                    emp.id, emp.name, emp.department, emp.age);
            }

        } catch (IOException e) {
            System.err.println("CSV写入失败：" + e.getMessage());
        }
    }
}

// ❌ 错误：程序退出前未关闭流，缓冲区数据丢失
BufferedWriter bw = new BufferedWriter(new FileWriter("report.txt"));
bw.write("飞翔科技月度报告");
bw.write("本期营收：500万元");
// 没有 bw.close() —— 文件可能为空或内容不完整！
System.exit(0);

// ✅ 正确：try-with-resources 确保 close()
try (BufferedWriter bw = new BufferedWriter(new FileWriter("report.txt"))) {
    bw.write("飞翔科技月度报告");
    bw.newLine();
    bw.write("本期营收：500万元");
} // 自动 close → flush → 数据完整落盘

// ❌ 错误：读出后直接写回，换行符丢失，所有行挤在一行
try (BufferedReader br = ...; BufferedWriter bw = ...) {
    String line;
    while ((line = br.readLine()) != null) {
        bw.write(line);  // 忘记 bw.newLine();
    }
}

// ✅ 正确：使用 newLine() 补充换行符
try (BufferedReader br = ...; BufferedWriter bw = ...) {
    String line;
    while ((line = br.readLine()) != null) {
        bw.write(line);
        bw.newLine();  // 补充平台相关的换行符
    }
}

// ❌ 错误：BufferedReader 需要 Reader 参数，不接收 InputStream
BufferedReader br = new BufferedReader(new FileInputStream("data.txt"));
// 编译错误！BufferedReader 的构造方法是 BufferedReader(Reader in)

// ✅ 正确：通过 InputStreamReader 搭桥
BufferedReader br = new BufferedReader(
    new InputStreamReader(new FileInputStream("data.txt"), "UTF-8"));