Web学习笔记 - 第006天

项目开发流程

可行性分析 --- 做还是不做
需求分析 --- 做什么
概要设计
详细设计

UML --- ROSE / StarUML / EA（Enterprise Architect）
数据库设计 --- ER图 PowerDesigner

验证码

例子1:

public final class CommonUtil {
    private static final String CHARS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    private static final int MAX_LEN = CHARS.length();
    private static final int MAX_THETA_DEGREE = 25;
    
    private CommonUtil() {
        throw new AssertionError();
    }
    
    public static int randomInt(int min, int max) {
        return (int) (Math.random() * (max - min)) + min;
    }
    
    public static Color randomColor() {
        int r = randomInt(0, 256);
        int g = randomInt(0, 256);
        int b = randomInt(0, 256);
        return new Color(r, g, b);
    }
    
    public static String verifyCodeStr(int len) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < len; i++) {
            char ch = CHARS.charAt(randomInt(0, MAX_LEN));
            sb.append(ch);
        }
        return sb.toString();
    }
    
    public static BufferedImage codeStrToImage(String codeStr, int width ,int height) {
        BufferedImage image = new BufferedImage(width, height, 1);
        Graphics g = image.getGraphics();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);
                for (int i = 0; i < 10; i++) {
            g.setColor(randomColor());
            g.drawLine(randomInt(0, 80), randomInt(0, 30),
                    randomInt(0, 80), randomInt(0, 30));
        }
        int size = (width - 20) / codeStr.length();
        size = size < height ? size : height;
        g.setFont(new Font("Consolas", Font.BOLD, size));
        for (int i = 0; i < codeStr.length(); i++) {
            char ch = codeStr.charAt(i);
            double theta = Math.PI / 180 / (i + 1) * 
                    randomInt(-MAX_THETA_DEGREE, MAX_THETA_DEGREE);
            ((Graphics2D) g).rotate(theta);
            g.setColor(randomColor());
            g.drawString(String.valueOf(ch), 10 + i * size, height / 2 + randomInt(4, 10));
            ((Graphics2D) g).rotate(-theta);
        }
        return image;
    }
}

例子2:

public final class MyUtil {
    public static final String CHARS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    public static final int UNIT_CODE_SIZE = 45;
    public static final int MAX_THETA_DEGREE = 15;
    
    private MyUtil() {
        throw new AssertionError();
    }
    
    public static Image generateImageVC(int len) {
        int width = UNIT_CODE_SIZE * len + 20;
        int height = UNIT_CODE_SIZE;
        BufferedImage image = new BufferedImage(width, height, 1);
        Graphics graphics = image.getGraphics();
        graphics.setColor(Color.WHITE);
        graphics.fillRect(0, 0, width, height);
        String vc = generateVC(len);
        int size = (int) (UNIT_CODE_SIZE * 0.618);
        graphics.setFont(new Font("Arial", Font.PLAIN, size));
        for (int i = 0; i < len; i++) {
            // 旋转画布后再绘制验证码(歪曲文字增加OCR的难度)
            double theta = Math.PI / 180 / (i + 1) * 
                    randomInt(-MAX_THETA_DEGREE, MAX_THETA_DEGREE);
            ((Graphics2D) graphics).rotate(theta);
            // 将画笔设置为随机颜色
            graphics.setColor(randomColor());
            int x = 20 + i * UNIT_CODE_SIZE;
            int y = 10 + (int) (UNIT_CODE_SIZE *0.382);
            graphics.drawString(vc.substring(i, i + 1), x, y);
            // 旋转后要将画布转回去否则多次的旋转会产生叠加效果
            ((Graphics2D) graphics).rotate(-theta);
        }
        return image;
    }
    
    public static String generateVC(int len) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < len; i++) {
            int randomIndex = (int) (Math.random() * CHARS.length());
            char ch = CHARS.charAt(randomIndex);
            sb.append(ch);
        }
        return sb.toString();
    }
    
    public static Color randomColor() {
        return new Color(randomInt(0, 255), randomInt(0, 255), randomInt(0, 255));
    }
    
    public static int randomInt(int min, int max) {
        return (int) (Math.random() * (max - min + 1) + min);
    }
    
    public static double randomDouble(double min, double max) {
        return Math.random() * (max - min + 1) + min;
    }
}

数据库

图片 - blob

photo blob, -- Binary Large Object 二进制大对象
clob -- Character

如果有xxx表就先删除

drop table if exists tb_dept;

外键

• 外键约束（参照完整性）

dno integer, 
/constraint fk_emp_dno/ foreign key(dno) references tb_dept(dno)

• 添加外键约束

alter table tb_emp add constraint fk_emp_dno foreign key (dno) references tb_dept
(dno) on update cascade on delete set null;

查询

• 查询所有行所有列

select * from tb_dept;
select * from tb_emp;

• 投影

select ename, job, sal from tb_emp;

• 别名 as 可以省略

select ename as 姓名, job as 职位, sal as 月薪 
from tb_emp;
select ename 姓名, job 职位, sal 月薪 
from tb_emp;

• 筛选

select ename, job, sal from tb_emp
where sal>=5000;
select ename, job, sal from tb_emp
where sal>=5000 or sal<=2000;
select ename, job, sal from tb_emp
where sal>=3000 and sal<=5000;
select ename, job, sal from tb_emp
where sal between 3000 and 5000;

• 模糊

select ename, job, sal from tb_emp
where ename like '张%'; -- %: 0个或任意多个字符
select ename, job, sal from tb_emp
where ename like '%张%';
select ename, job, sal from tb_emp
where ename like '张_'; -- _: 精确匹配一个字符

• 排序

select ename, job, sal from tb_emp
where ename like '张%' order by sal; -- 默认升序asc
select ename, job, sal from tb_emp
where ename like '张%' order by sal desc;

• 连接
• 自然连接

select ename, job, sal, dname 
from tb_emp as t1, tb_dept as t2
where t1.dno=t2.dno and ename like '张%';

• 内连接 先写连表条件，后写筛选条件

select ename, job, sal, dname 
from tb_emp as t1 inner join tb_dept as t2
on t1.dno=t2.dno;

• 分组查询/聚合函数

select max(sal) as maxSal from tb_emp;
select min(sal) as minSal from tb_emp;
select avg(sal) as avgSal from tb_emp;
select sum(sal) as sumSal from tb_emp;
select count(sal) as total from tb_emp;

select dno, avg(sal) from tb_emp
group by dno;

• 子查询 把一个查询的结果拿来作为另一个查询的条件和结果来使用

select dname, total from
(select dno, count(dno) as total from tb_emp
group by dno) as t1 inner join tb_dept as t2
on t1.dno=t2.dno;

select ename, job, sal from tb_emp
where sal=(select max(sal) from tb_emp);

• 分页

select * from tb_emp 
order by sal desc limit 0,5;
select * from tb_emp
order by sal desc limit 5,5;
select * from tb_emp
order by sal desc limit 10,5;

作业

• 4.求挣最高薪水的员工（BOSS除外）的姓名

select ename, max(sal) from tb_emp where job<>'总裁';

• 5.查询薪水超过平均薪水的员工的姓名和工资

select ename, sal from tb_emp as t1,
(select avg(sal) as avgSal from tb_emp) as t2
where t1.sal>=t2.avgSal;

• 6.查询薪水超过其所在部门平均薪水的员工的姓名和工资

select ename, sal, avgSal from
(select dno, avg(sal) as avgSal from tb_emp group by dno) as t1, 
tb_emp as t2 
where t1.dno=t2.dno and t2.sal>t1.avgSal;

• 7.查询部门中薪水最高的人姓名、工资和所在部门名称

select ename, sal, dname from 
(select dname, maxSal from
(select dno, max(sal) as maxSal from tb_emp group by dno) as t1 inner join tb_dept as t2
on t1.dno=t2.dno) as t3, tb_emp as t4
where t3.maxSal=t4.sal;

• 8.哪些人是主管

select ename from
(select mgr from tb_emp group by mgr) as t1, tb_emp as t2
where t1.mgr=t2.eno;