ACL:Access Control List  访问控制列表

1.  简介

0.概述

ACL 权限控制,使用:scheme:id:perm 来标识,主要涵盖 3 个方面:
  权限模式(Scheme):授权的策略
  授权对象(ID):授权的对象
  权限(Permission):授予的权限

其特性如下:
  ZooKeeper的权限控制是基于每个znode节点的,需要对每个节点设置权限
  每个znode支持设置多种权限控制方案和多个权限
  子节点不会继承父节点的权限,客户端无权访问某节点,但可能可以访问它的子节点

例如:

setAcl /test2 ip:128.0.0.1:crwda

1.  scheme  采用何种方式授权

  world:默认方式,相当于全部都能访问
  auth:代表已经认证通过的用户(cli中可以通过addauth digest user:pwd 来添加当前上下文中的授权用户)
  digest:即用户名:密码这种方式认证,这也是业务系统中最常用的。用 username:password 字符串来产生一个MD5串,然后该串被用来作为ACL ID。认证是通过明文发送username:password 来进行的,当用在ACL时,表达式为username:base64 ,base64是password的SHA1摘要的编码。
  ip:使用客户端的主机IP作为ACL ID 。这个ACL表达式的格式为addr/bits ,此时addr中的有效位与客户端addr中的有效位进行比对。

2.  ID   给谁授予权限

  授权对象ID是指,权限赋予的用户或者一个实体,例如:IP 地址或者机器。授权模式 schema 与 授权对象 ID 之间

3.  permission   授予什么权限

  CREATE、READ、WRITE、DELETE、ADMIN 也就是 增、删、改、查、管理权限,这5种权限简写为crwda

注意:

  这5种权限中,delete是指对子节点的删除权限,其它4种权限指对自身节点的操作权限

更详细的如下:

  CREATE   c 可以创建子节点
  DELETE   d 可以删除子节点(仅下一级节点)
  READ       r 可以读取节点数据及显示子节点列表
  WRITE     w 可以设置节点数据
  ADMIN     a 可以设置节点访问控制列表权限

2.ACL 相关命令

getAcl        getAcl <path>     读取ACL权限
setAcl        setAcl <path> <acl>     设置ACL权限
addauth      addauth <scheme> <auth>     添加认证用户

3.测试zkCli设置权限

1.word方式

[zk: localhost:(CONNECTED) ] create /test1 test1-value
Created /test1
[zk: localhost:(CONNECTED) ] getAcl /test1 #创建的默认是所有用户都可以进行cdrwa
'world,'anyone
: cdrwa
[zk: localhost:(CONNECTED) ] setAcl /test1 world:anyone:acd #修改为所有人可以acd
cZxid = 0x400000007
ctime = Tue Mar :: CST
mZxid = 0x400000007
mtime = Tue Mar :: CST
pZxid = 0x400000007
cversion =
dataVersion =
aclVersion =
ephemeralOwner = 0x0
dataLength =
numChildren =
[zk: localhost:(CONNECTED) ] getAcl /test1
'world,'anyone
: cda

2.IP的方式

[zk: localhost:(CONNECTED) ] create /test2 test2-value
Created /test2
[zk: localhost:(CONNECTED) ] setAcl /test2 ip:127.0.0.1:crwda #修改此IP具有所有权限
cZxid = 0x400000009
ctime = Tue Mar :: CST
mZxid = 0x400000009
mtime = Tue Mar :: CST
pZxid = 0x400000009
cversion =
dataVersion =
aclVersion =
ephemeralOwner = 0x0
dataLength =
numChildren =
[zk: localhost:(CONNECTED) ] getAcl /test2
'ip,'127.0.0.1
: cdrwa

 当然可以设置IP的时候使用多个ip的方式,比如:

[zk: localhost:(CONNECTED) ] setAcl /t3 ip:192.168.0.164:cdwra,ip:127.0.0.1:cdwra
cZxid = 0x400000018
ctime = Tue Mar :: CST
mZxid = 0x400000018
mtime = Tue Mar :: CST
pZxid = 0x400000018
cversion =
dataVersion =
aclVersion =
ephemeralOwner = 0x0
dataLength =
numChildren =
[zk: localhost:(CONNECTED) ] getAcl /t3
'ip,'192.168.0.164
: cdrwa
'ip,'127.0.0.1
: cdrwa

3.  Auth

[zk: localhost:(CONNECTED) ] create /t4
Created /t4
[zk: localhost:(CONNECTED) ] addauth digest qlq:111222 #增加授权用户,明文用户名和密码
[zk: localhost:(CONNECTED) ] setAcl /t4 auth:qlq:cdwra  #授予权限
cZxid = 0x40000001d
ctime = Tue Mar :: CST
mZxid = 0x40000001d
mtime = Tue Mar :: CST
pZxid = 0x40000001d
cversion =
dataVersion =
aclVersion =
ephemeralOwner = 0x0
dataLength =
numChildren =
[zk: localhost:(CONNECTED) ] getAcl /t4
'digest,'qlq:JWNEexxIoeVompjU7O5pZzTU+VQ=
: cdrwa

 如果重新连接之后获取会报没权限,需要添加授权用户:

[zk: localhost:(CONNECTED) ] get /t4
Authentication is not valid : /t4
[zk: localhost:(CONNECTED) ] addauth digest qlq:
[zk: localhost:(CONNECTED) ] get /t4 cZxid = 0x40000001d
ctime = Tue Mar :: CST
mZxid = 0x40000001d
mtime = Tue Mar :: CST
pZxid = 0x40000001d
cversion =
dataVersion =
aclVersion =
ephemeralOwner = 0x0
dataLength =
numChildren =

4. Digest

etAcl /test digest:用户名:密码:权限 

  密码是用户名和密码加密后的字符串。

(1)生成密码:sha1加密之后base64编码

package zd.dms.test;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.apache.commons.codec.binary.Base64; public class Test {
public static void main(String[] args) throws NoSuchAlgorithmException {
String usernameAndPassword = "user:123456";
byte digest[] = MessageDigest.getInstance("SHA1").digest(usernameAndPassword.getBytes());
Base64 base64 = new Base64();
String encodeToString = base64.encodeToString(digest);
System.out.println(encodeToString);
}
}

6DY5WhzOfGsWQ1XFuIyzxkpwdPo=

(2)设置权限

[zk: localhost:(CONNECTED) ] setAcl /t6  digest:user:6DY5WhzOfGsWQ1XFuIyzxkpwdPo=:crwda  #授权
cZxid = 0x400000028
ctime = Tue Mar :: CST
mZxid = 0x400000028
mtime = Tue Mar :: CST
pZxid = 0x400000028
cversion =
dataVersion =
aclVersion =
ephemeralOwner = 0x0
dataLength =
numChildren =
[zk: localhost:(CONNECTED) ] getAcl /t6
'digest,'user:6DY5WhzOfGsWQ1XFuIyzxkpwdPo=
: cdrwa

直接删除会不允许,也必须增加摘要之后才能删除

[zk: localhost:(CONNECTED) ] rmr /t6   #直接删除没权限
Authentication is not valid : /t6
[zk: localhost:(CONNECTED) ] addauth digest user:123456 #增加认证用户
[zk: localhost:(CONNECTED) ] rmr /t6
[zk: localhost:(CONNECTED) ] ls /
[t4, curator, test2, zookeeper, test1, t3]

5.Java原生的zookeperAPI的ACL

1.创建节点回顾

原来我们创建节点的时候如下:

package zookeper;

import java.io.IOException;
import java.util.concurrent.CountDownLatch; import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper; public class BaseAPI {
private static ZooKeeper zoo;
final static CountDownLatch connectedSignal = new CountDownLatch(1); public static ZooKeeper connect(String host) throws IOException, InterruptedException {
zoo = new ZooKeeper(host, 5000, new Watcher() {
public void process(WatchedEvent event) {
if (event.getState() == KeeperState.SyncConnected) {
connectedSignal.countDown();
}
}
}); connectedSignal.await();
return zoo;
} public void close() throws InterruptedException {
zoo.close();
} public static void create(String path, byte[] data) throws KeeperException, InterruptedException {
zoo.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
} public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
final String path = "/t7";
final ZooKeeper connect = connect("127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183");
connect.create(path, "777".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
Thread.sleep(10 * 1000);
} }

可以看到create方法的第三个参数就是ACL集合,使用的是与zkCli方式一样的word:anyone:crwda 默认方式

如下:

        /**
* This is a completely open ACL .
*/
public final ArrayList<ACL> OPEN_ACL_UNSAFE = new ArrayList<ACL>(
Collections.singletonList(new ACL(Perms.ALL, ANYONE_ID_UNSAFE))); public interface Perms {
int READ = 1 << 0; int WRITE = 1 << 1; int CREATE = 1 << 2; int DELETE = 1 << 3; int ADMIN = 1 << 4; int ALL = READ | WRITE | CREATE | DELETE | ADMIN;
} public interface Ids {
public final Id ANYONE_ID_UNSAFE = new Id("world", "anyone"); public final Id AUTH_IDS = new Id("auth", ""); public final ArrayList<ACL> OPEN_ACL_UNSAFE = new ArrayList<ACL>(
Collections.singletonList(new ACL(Perms.ALL, ANYONE_ID_UNSAFE))); public final ArrayList<ACL> CREATOR_ALL_ACL = new ArrayList<ACL>(
Collections.singletonList(new ACL(Perms.ALL, AUTH_IDS))); public final ArrayList<ACL> READ_ACL_UNSAFE = new ArrayList<ACL>(
Collections
.singletonList(new ACL(Perms.READ, ANYONE_ID_UNSAFE)));
}

自己手动写一个采用IP的方式设置ACL的方法:

package zookeper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch; import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooDefs.Perms;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;
import org.apache.zookeeper.data.Id; public class BaseAPI {
private static ZooKeeper zoo;
final static CountDownLatch connectedSignal = new CountDownLatch(1); public static ZooKeeper connect(String host) throws IOException, InterruptedException {
zoo = new ZooKeeper(host, 5000, new Watcher() {
public void process(WatchedEvent event) {
if (event.getState() == KeeperState.SyncConnected) {
connectedSignal.countDown();
}
}
}); connectedSignal.await();
return zoo;
} public void close() throws InterruptedException {
zoo.close();
} public static void create(String path, byte[] data) throws KeeperException, InterruptedException {
zoo.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
} public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
final String path = "/t9";
final ZooKeeper connect = connect("127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183"); // 创建ACL
ACL acl = new ACL();
// 创建Id,也可以设置构造方法传入scheme和id
Id id = new Id("ip", "192.168.0.164");
acl.setId(id);
acl.setPerms(Perms.ALL); List<ACL> acls = new ArrayList<>();
acls.add(acl); connect.create(path, "777".getBytes(), acls, CreateMode.PERSISTENT);
Thread.sleep(10 * 1000);
} }

获取ACL:

package zookeper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch; import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooDefs.Perms;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;
import org.apache.zookeeper.data.Id; public class BaseAPI {
private static ZooKeeper zoo;
final static CountDownLatch connectedSignal = new CountDownLatch(1); public static ZooKeeper connect(String host) throws IOException, InterruptedException {
zoo = new ZooKeeper(host, 5000, new Watcher() {
public void process(WatchedEvent event) {
if (event.getState() == KeeperState.SyncConnected) {
connectedSignal.countDown();
}
}
}); connectedSignal.await();
return zoo;
} public void close() throws InterruptedException {
zoo.close();
} public static void create(String path, byte[] data) throws KeeperException, InterruptedException {
zoo.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
} public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
final String path = "/t9";
final ZooKeeper connect = connect("127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183"); List<ACL> acls = connect.getACL("/t9", connect.exists("/t9", false));
for (ACL acl : acls) {
System.out.println(acl.getPerms());
System.out.println(acl.getId());
}
} }

结果:

31
'ip,'192.168.0.164

ckCli客户端进行验证:

[zk: localhost:(CONNECTED) ] getAcl /t9
'ip,'192.168.0.164
: cdrwa

补充:权限的计算方法:

<<:左移位,在低位处补0;  &与(AND),对两个整型操作数中对应位执行布尔代数,两个位都为1时输出1,否则0。

1

10

100

1000

10000

按位与之后是:11111  也就是十进制的31.

2.修改ACL

  修改节点   /t10 节点的acl访问方式采用digest:user:111222

package zookeper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch; import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooDefs.Perms;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;
import org.apache.zookeeper.data.Id;
import org.apache.zookeeper.data.Stat; public class BaseAPI {
private static ZooKeeper zoo;
final static CountDownLatch connectedSignal = new CountDownLatch(1); public static ZooKeeper connect(String host) throws IOException, InterruptedException {
zoo = new ZooKeeper(host, 5000, new Watcher() {
public void process(WatchedEvent event) {
if (event.getState() == KeeperState.SyncConnected) {
connectedSignal.countDown();
}
}
}); connectedSignal.await();
return zoo;
} public void close() throws InterruptedException {
zoo.close();
} public static void create(String path, byte[] data) throws KeeperException, InterruptedException {
zoo.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
} public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
final String path = "/t10";
final ZooKeeper connect = connect("127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183"); // 创建ACL
ACL acl = new ACL();
// 创建Id,也可以设置构造方法传入scheme和id
Id id = new Id("digest", "user:6DY5WhzOfGsWQ1XFuIyzxkpwdPo=");
acl.setId(id);
acl.setPerms(Perms.ALL); List<ACL> acls = new ArrayList<>();
acls.add(acl); // 修改ACL
Stat setACL = connect.setACL(path, acls, connect.exists(path, false).getAversion()); // 获取Acl
System.out.println(connect.getACL(path, setACL));
}
}

结果:

[31,s{'digest,'user:6DY5WhzOfGsWQ1XFuIyzxkpwdPo=}
]

zkCli客户端进行验证:

[zk: localhost:(CONNECTED) ] getAcl /t10
'digest,'user:6DY5WhzOfGsWQ1XFuIyzxkpwdPo=
: cdrwa

3.访问上面的节点会报错没权限

package zookeper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch; import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooDefs.Perms;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;
import org.apache.zookeeper.data.Id;
import org.apache.zookeeper.data.Stat; public class BaseAPI {
private static ZooKeeper zoo;
final static CountDownLatch connectedSignal = new CountDownLatch(1); public static ZooKeeper connect(String host) throws IOException, InterruptedException {
zoo = new ZooKeeper(host, 5000, new Watcher() {
public void process(WatchedEvent event) {
if (event.getState() == KeeperState.SyncConnected) {
connectedSignal.countDown();
}
}
}); connectedSignal.await();
return zoo;
} public void close() throws InterruptedException {
zoo.close();
} public static void create(String path, byte[] data) throws KeeperException, InterruptedException {
zoo.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
} public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
final String path = "/t10";
final ZooKeeper connect = connect("127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183");
byte[] data = connect.getData(path, false, null);
System.out.println(new String(data, "UTF-8"));
}
}

结果:

log4j:WARN No appenders could be found for logger (org.apache.zookeeper.ZooKeeper).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" org.apache.zookeeper.KeeperException$NoAuthException: KeeperErrorCode = NoAuth for /t10
at org.apache.zookeeper.KeeperException.create(KeeperException.java:113)
at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1212)
at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1241)
at zookeper.BaseAPI.main(BaseAPI.java:42)

4.    解决办法:连接的connection增加用户信息

package zookeper;

import java.io.IOException;
import java.util.concurrent.CountDownLatch; import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper; public class BaseAPI {
private static ZooKeeper zoo;
final static CountDownLatch connectedSignal = new CountDownLatch(1); public static ZooKeeper connect(String host) throws IOException, InterruptedException {
zoo = new ZooKeeper(host, 5000, new Watcher() {
public void process(WatchedEvent event) {
if (event.getState() == KeeperState.SyncConnected) {
connectedSignal.countDown();
}
}
}); connectedSignal.await();
return zoo;
} public void close() throws InterruptedException {
zoo.close();
} public static void create(String path, byte[] data) throws KeeperException, InterruptedException {
zoo.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
} public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
final String path = "/t10";
final ZooKeeper connect = connect("127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183"); // 会话添加用户和密码信息
connect.addAuthInfo("digest", "user:123456".getBytes()); byte[] data = connect.getData(path, false, null);
System.out.println(new String(data, "UTF-8"));
}
}

结果:

10

zookeeper的ACL权限控制的更多相关文章

  1. ZooKeeper设置ACL权限控制

    ZK的节点有5种操作权限:CREATE.READ.WRITE.DELETE.ADMIN 也就是 增.删.改.查.管理权限,这5种权限简写为crwda(即:每个单词的首字符缩写)注:这5种权限中,del ...

  2. 1.ZooKeeper ACL权限控制

    参考:https://blog.csdn.net/liuxiao723846/article/details/79391650 ZK 类似文件系统,Client 可以在上面创建节点.更新节点.删除节点 ...

  3. Linux系统——ACL权限控制及特殊权限

    ACL权限控制 ACL(access control list),可以提供除属主.属组.其他人的rwx权限之外的细节权限设定 ACL的权限控制 (1)User 使用者 (2)Group 群组 (3)M ...

  4. phalcon: 目录分组后的acl权限控制

    phalcon: 目录分组后的acl权限控制 楼主在做acl权限的时候,发现官方的acl只能针对未分组的目录,如下: app/ ___|./controller ___|./logic ___|./p ...

  5. ZooKeeper学习之路(五)—— ACL权限控制

    一.前言 为了避免存储在Zookeeper上的数据被其他程序或者人为误修改,Zookeeper提供了ACL(Access Control Lists)进行权限控制.只有拥有对应权限的用户才可以对节点进 ...

  6. ZooKeeper系列(五)—— ACL 权限控制

    一.前言 为了避免存储在 Zookeeper 上的数据被其他程序或者人为误修改,Zookeeper 提供了 ACL(Access Control Lists) 进行权限控制.只有拥有对应权限的用户才可 ...

  7. 面试题解析|ACL权限控制机制

    ACL(Access Control List)访问控制列表 包括三个方面: 一.权限模式(Scheme) 1.IP:从 IP 地址粒度进行权限控制 2.Digest:最常用,用类似于 usernam ...

  8. ZooKeeper的ACL权限

    ACL控制权限 什么是ACL(Access Control List访问控制列表) 针对节点可以设置相关读写等权限, 目的为了保障数据安全性 权限permission可以指定不同的权限范围以及角色 A ...

  9. ACL 权限控制机制 ?

    UGO(User/Group/Others) 目前在 Linux/Unix 文件系统中使用,也是使用最广泛的权限控制方式.是一种粗 粒度的文件系统权限控制模式. ACL(Access Control ...

随机推荐

  1. windows server 2012 流媒体服务器搭建(直播与点播)

    IIS Live Smooth Streaming(实时平滑流式处理)是微软下一代流媒体解决方案.该技术是在IIS web中集成媒体传输平台IIS media services,实现利用标准 HTTP ...

  2. mysql 5.7安装准备

    在5.5之后的mysql安装中,需要使用cmake来指定安装参数,下面列出关于cmake的几个常用参数: CMAKE_INSTALL_PREFIX:指定MySQL程序的安装目录,默认/usr/loca ...

  3. python对象初始化

    当python对象被创建以后,需要将对象进行初始化.Python有一个构造函数和一个初始化函数: 1.构造函数__new__,只接受一个参数,即类本身(它会在对象被构造之前调用,所以这里也就没有sel ...

  4. HDU 1023(卡特兰数 数学)

    题意是求一列连续升序的数经过一个栈之后能变成的不同顺序的数目. 开始时依然摸不着头脑,借鉴了别人的博客之后,才知道这是卡特兰数,卡特兰数的计算公式是:a( n )  =  ( ( 4*n-2 ) / ...

  5. HDU 1006(时钟指针转角 **)

    题意是说求出在一天中时针.分针.秒针之间距离均在 D 度以上的时间占比. 由于三针始终都在转动,所以要分别求出各个针之间的相对角速度,分别求出三针满足角度差的首次时间,再分别求出不满足角度差的最终时间 ...

  6. HDU 6373(斜面上小球弹跳 运动分解)

    题意是给定两个点的位置,过原点引一条射线穿过第一个点,射线位置作为斜面位置,第二个点处令一小球自由落体,问小球能碰撞到斜面几次. 开始时想算出两次碰撞中小球沿斜面运动的距离,然后发现每一段距离会因为高 ...

  7. Part-Ten

    1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

  8. Golang入门教程(十)内建函数

    比较常用的内建函数 参考: http://blog.csdn.net/liumiaocn/article/details/54804074

  9. js/java常用正则表达式及写法

    不定时增加正则表达式. 其中 Js验证写法: var str = "待验证文本"; var regular = new RegExp(/^这里是正则表达式/); if (regul ...

  10. 细说java系列之反射

    什么是反射 反射机制允许在Java代码中获取被JVM加载的类信息,如:成员变量,方法,构造函数等. 在Java包java.lang.reflect下提供了获取类和对象反射信息的相关工具类和接口,如:F ...