1、文档

xp 安装jdk
jdk下载
@Scheduled参数解析
SynchronousQueue解析：同时处理的任务不能超过最大线程数，这个队列用来保存同步
SQLException: validateConnection false
自定义Protostuff方式的RedisSerializer
获取byte的各个bit值以及常见位操作
Java8 Stream：2万字20个实例，玩转集合的筛选、归约、分组、聚合
创建ByteBuf对象,读写原理
自定义logback打印颜色
自定义连接池
springboot和springsecurity整合OAuth2
构建树形节点
jar加密
java正则
自定义类加载器加载冲突类
加载多个相同类名的jar
获取对象内存地址
可视化代码执行

2、相关问题

2.1、两个list集合的交集、差集、并集

描述：

list1集合和list2集合的交集、差集、并集
解决同步问题

解决方案：

问题的解决方案

    @org.junit.Test
    public void test(){
        List<String> list1 = new ArrayList<String>();
        list1.add("1");
        list1.add("2");
        list1.add("3");
        list1.add("5");
        list1.add("6");
        List<String> list2 = new ArrayList<String>();
        list2.add("2");
        list2.add("3");
        list2.add("7");
        list2.add("8");
        // 交集
        List<String> intersection = list1.stream().filter(item -> list2.contains(item)).collect(toList());
        System.out.println("---交集 intersection---");
        intersection.parallelStream().forEach(System.out :: println);
        // 差集 (list1 - list2)
        List<String> reduce1 = list1.stream().filter(item -> !list2.contains(item)).collect(toList());
        System.out.println("---差集 reduce1 (list1 - list2)---");
        reduce1.parallelStream().forEach(System.out :: println);
        // 差集 (list2 - list1)
        List<String> reduce2 = list2.stream().filter(item -> !list1.contains(item)).collect(toList());
        System.out.println("---差集 reduce2 (list2 - list1)---");
        reduce2.parallelStream().forEach(System.out :: println);
        // 并集
        List<String> listAll = list1.parallelStream().collect(toList());
        List<String> listAll2 = list2.parallelStream().collect(toList());
        listAll.addAll(listAll2);
        System.out.println("---并集 listAll---");
        listAll.parallelStream().forEachOrdered(System.out :: println);
        // 去重并集
        List<String> listAllDistinct = listAll.stream().distinct().collect(toList());
        System.out.println("---得到去重并集 listAllDistinct---");
        listAllDistinct.parallelStream().forEachOrdered(System.out :: println);
        System.out.println("---原来的List1---");
        list1.parallelStream().forEachOrdered(System.out :: println);
        System.out.println("---原来的List2---");
        list2.parallelStream().forEachOrdered(System.out :: println);
    }

2.2、ThreadPoolExecutor线程池使用

描述：

LinkedBlockingQueue 默认无界

解决方案：

@Slf4j
public class Test {
  private int count = 6;
  private CountDownLatch countDownLatch = new CountDownLatch(count);
  @org.junit.Test
  public void test() throws InterruptedException {
      ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2, 4, 30, TimeUnit.SECONDS, new LinkedBlockingQueue<>(10));
      for (int i = 0; i < count; i++) {
          threadPoolExecutor.execute(new Runnable() {
              @Override
              public void run() {
                  log.info("===============");
                  try {
                      countDownLatch.await();
                  } catch (InterruptedException e) {
                      e.printStackTrace();
                  }
              }
          });
          countDownLatch.countDown();
      }
      System.out.println("end");
      Thread.sleep(3000);
  }
  public static void main(String[] args) throws InterruptedException, UnknownHostException {
  }
}

2.3、命令行编译打包

描述：

通过jdk的工具使用命令来进行java项目的编译打包

解决方案：

编译

# 将class文件生成到指定的targer目录
javac src/com/demo/Hello.java -d target

打包

# -C target . 参数，指定把 target 目录下的所有文件打包。注意，需要从包名开始打包
jar -cvf my.jar -C target .
# 指定com目录下所有class文件打包，报名为my.jar
jar -cvf my.jar -C target com

添加主类：
打包好后现在还不能执行，需要添加主类；

在jar中打开META-INF/MANIFEST.MF 指定主类
Main-Class: com.demo.Hello

执行

java -jar my.jar

2.4、打包

2.4.1、不指定主类（maven）

2.4.1.1、不带依赖

<build>
  <finalName>demo</finalName>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <configuration>
        <encoding>UTF-8</encoding>
        <source>8</source>
        <target>8</target>
      </configuration>
    </plugin>
  </plugins>
</build>

2.4.1.2、带依赖

 <build>
        <finalName>${name}-${version}</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <encoding>UTF-8</encoding>
                    <source>8</source>
                    <target>8</target>
                </configuration>
            </plugin>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <configuration>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id> <!-- this is used for inheritance merges -->
                        <phase>package</phase> <!-- bind to the packaging phase -->
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

2.4.2、指定主类（maven）

2.4.2.1、不带依赖

<build>
        <finalName>demo</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <encoding>UTF-8</encoding>
                    <source>8</source>
                    <target>8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

手动在jar中MANIFEST.MF中加入Main-Class:属性，指定主类

2.4.2.2、带依赖

 <build>
        <finalName>${name}-${version}</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <encoding>UTF-8</encoding>
                    <source>8</source>
                    <target>8</target>
                </configuration>
            </plugin>
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <configuration>
                    <archive>
                        <manifest>
                            <mainClass>com.lms.maven.jar.Test2</mainClass>
                        </manifest>
                    </archive>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id> <!-- this is used for inheritance merges -->
                        <phase>package</phase> <!-- bind to the packaging phase -->
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

2.4.2.4、带外部依赖（lib/）

第一种：把lib加入库，添加如下就可以使用，不需要添加依赖坐标

<build>
        <resources>
            <resource>
                <directory>lib</directory>
                <targetPath>/BOOT-INF/lib/</targetPath>
                <includes>
                    <include>**/*.jar</include>
                </includes>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.1.18.RELEASE</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

第二种:需要添加引用

<build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.1.18.RELEASE</version>
                <configuration>
                    <!-- 打包本地库-->
                    <includeSystemScope>true</includeSystemScope>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

2.5、maven打包时给jar包起一个固定的名字

 <build>
        <finalName>${parent.artifactId}</finalName>
    </build>

2.6、Error attempting to get column ‘create_time’ from result set.

Error attempting to get column ‘create_time’ from result set. Cause: java.sql.SQLFeatureNotSupported

https://blog.csdn.net/weixin_39520967/article/details/99706639
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
<version>1.1.18</version>
</dependency>
druid的版本升级到1.1.18以上就可

2.7、获取打jar包后的资源文件路径

jar包执行时访问资源文件造成的FileSystemNotFoundException问题
使用

 properties = new Properties();
        URL url = DmdbSqlConfig.class.getClassLoader().getResource("dmsql");
        if (url != null) {
            Path path = Paths.get(url.toURI());
            Files.walkFileTree(path, new SimpleFileVisitor<Path>() {
                @Override
                public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
                    log.info("加载sql文件:{}", file);
                    properties.load(new FileInputStream(new File(file.toUri())));
                    return super.visitFile(file, attrs);
                }
            });
        }

在idea中使用没有问题，但是打成jar包在服务器上执行的时候会出现异常，
解决办法：通过spring注解来解决


@Value("classpath:/dmsql/**")
private Resource[] sqlResources;
public void loadSql() {
    Stream.of(sqlResources).forEach(sqlResources -> {
            try (InputStream is = sqlResources.getInputStream()) {
                log.info("加载sql文件:{}", sqlResources.getFilename());
                properties.load(is);
            } catch (Exception e) {
                e.printStackTrace();
                throw new RuntimeException("导入sql语句异常" + e.getMessage());
            }
        });
}
或手动注入
ResourcePatternResolver resolver = ResourcePatternUtils.getResourcePatternResolver(new DefaultResourceLoader());
Resource[] resources = resolver.getResources("classpath:/dmsql/*/*");
for (Resource resource : resources) {
    System.out.println(resource);
}

2.8、线程诊断cpu占用过高

1、先用top命令查看哪一个java程序占用cpu过高
2、再用**ps H -eo pid,tid,%cpu | grep 进程id ** 查看哪一个线程占用cpu过高
3、将线程id换算成16进制
4、使用**jstack 进程id**查看所有的java线程，找到具体的线程，根据换算来的id查找

2.9、程序结束前动作

Runtime runtime = Runtime.getRuntime();
runtime.addShutdownHook(new Thread(() -> System.out.println("程序退出前动作")));

注意：这个适合在正常关闭程序才会执行，断电，直接杀死进程是不会执行的

2.10、指定编码去读取properties文件

properties = new Properties();
properties.load(new InputStreamReader(is, StandardCharsets.UTF_8));
// 或者在取值的时候手动转换编码：new String(value.getBytes("ISO-8859-1"),"UTF-8");

只能学一点点

Java:文档以及相关问题