This article organizes my own commonly used jar packages and commonly used API records in Java development.
1. common-lang3
Introduction: A jar package that is now the most commonly used, encapsulating many commonly used tool packages
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Dependency:
<!-- https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 -->
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.4</version>
</dependency>The main common classes are as follows:
Array Tool class ArrayUtils
Date tool class DateUtils DateFormatUtils
String tool class StringUtils
Number tool class NumberUtils
Boolean tool class BooleanUtils
Reflection related tool classes FieldUtils, MethodUtils, MemberUtils, TypeUtils, ConstructorUtils
Object tool class ObjectUtils
Serialization tool class SerializationUtils
API introduction
Here I will only introduce a few frequently used tool classes and methods, ArrayUtils, StringUtils, NumberUtils, DateUtils. For others, please check the official API documentation
1.ArrayUtils
| Method name | Description |
|---|---|
| add | |
| remove | |
| Copy array | |
| The second parameter is passed in the subscript to be deleted (Multiple subscripts can be specified) | |
| Convert the value (int[], double[]) to the packaging class (Int[], Double[] ) | |
| Search in order in the array and find the first index that satisfies the corresponding value | |
| Search the array in order and find the last subscript that satisfies the corresponding value | |
| Whether the array contains a certain value | |
| Determine whether the array is empty | |
| Determine whether the array is not empty | |
| Array reversal | |
| Specify the interval to intercept the array. The interval is a half-open interval and does not contain At the end | |
| Receives multiple objects and converts these objects into arrays of corresponding types | |
| Convert a two-dimensional array to a Map |
| max | |
| createInt | |
| toInt | |
| compare | |
| isDigits | |
| isParsable | |
| isNumber | |
| isSameDay | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| isSameDay | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| addHour | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DateFormatUtils, as its name suggests, is used to convert time into a string, so I won’t say more here 4.StringUtils
我们主要使用这四个：Error>Warn>Info>Debug 使用 我们可以使用两种方式来运行Log4j，一种是java代码方式，另外一种则是配置文件方式 例子（Java方式） public class Log4JTest {
public static void main(String[] args) {
//获取Logger对象的实例（传入当前类）
Logger logger = Logger.getLogger(Log4JTest.class);
//使用默认的配置信息，不需要写log4j.properties
BasicConfigurator.configure();
//设置日志输出级别为WARN，这将覆盖配置文件中设置的级别，只有日志级别低于WARN的日志才输出
logger.setLevel(Level.WARN);
logger.debug("这是debug");
logger.info("这是info");
logger.warn("这是warn");
logger.error("这是error");
logger.fatal("这是fatal");
}
}Copy after login 例子（配置文件方式） 上面的例子，我们想要实现打印Log，但是每次都要写一遍，浪费时间和精力，所以，Log4j提供了另外一种方式来配置好我们的信息 创建一个名为log4j.properties的文件，此文件需要放在项目的根目录（约定），如果是maven项目，直接放在resources文件夹中即可 log4j.properties #控制台
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n
#log jdbc
log4j.logger.java.sql.ResultSet=INFO
log4j.logger.org.apache=WARN
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG
#log mybatis设置
#log4j.logger.org.apache.ibatis=DEBUG
log4j.logger.org.apache.ibatis.jdbc=error
log4j.logger.org.apache.ibatis.io=info
log4j.logger.org.apache.ibatis.datasource=info
#springMVC日志
log4j.logger.org.springframework.web=WARN
# 文件输出配置
log4j.appender.A = org.apache.log4j.DailyRollingFileAppender
log4j.appender.A.File = D:/log.txt #指定日志的输出路径
log4j.appender.A.Append = true
log4j.appender.A.Threshold = DEBUG
log4j.appender.A.layout = org.apache.log4j.PatternLayout #使用自定义日志格式化器
log4j.appender.A.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss} [ %t:%r ] - [ %p ] %m%n #指定日志的输出格式
log4j.appender.A.encoding=UTF-8 #指定日志的文件编码
#指定日志的输出级别与输出端
log4j.rootLogger=DEBUG,Console,A
#指定某个包名日志级别（不能超过上面定义的级别，否则日志不会输出）
log4j.logger.com.wan=DEBUGCopy after login 之后使用的话就比较简单了 //Logger的初始化（这个推荐定义为全局变量，方便使用）
Logger logger = Logger.getLogger(Log4JTest.class);
//输出Log
logger.info("这是info");Copy after login 四、lombok 简介：平常我们创建实体类的时候，需要get/set方法，极其麻烦，虽然IDEA等IDE都是有提供了快捷生成，不过，最好的解决方法还是省略不写 而lombok就是这样的一个框架，实现省略get/set方法，当然，lombok的功能不只有此，还有equal，toString方法也可以由此框架自动生成 lombok的原理是使用注解，之后就会在编译过程中，给Class文件自动加上get/set等方法 不过IDEA似乎无法识别，代码检查还是会报错，所以，使用IDEA的时候还得安装一个插件，在plugin搜索lombok，之后安装重启即可，如图
之后为Java项目添加依赖 <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.8</version>
<scope>provided</scope>
</dependency>Copy after login 使用示例 1.实体类省略get/set 估计Kotlin中的data关键字就是参照着lombok实现的 //这里我们只需要为类添加Data注解，就会自动生成对应属性的get/set方法，toString，equal等方法
@Data
public class User {
private String username;
private String password;
}Copy after login 2.需要无参构造以及get/set方法 @Getter
@Setter
@NoArgsConstructor
public class User {
private String username;
private String password;
}Copy after login 3.链式调用set方法 @Data
@Accessors(chain = true)
public class User {
private String username;
private String password;
}
//使用
User user = new User();
user.setUsername("helo").setPassword("123");Copy after login 4.参数不为空 //如果调用此方法，就会抱一个空指针错误
public String print(@NotNull String str){
...
}Copy after login 5.只需要toString @ToString(callSuper=true, includeFieldNames=true)
public class User {
private String username;
private String password;
//省略的get/set方法
}Copy after login 6.builder模式创建实体类对象 @Data
@Builder
public class User {
private String username;
private String password;
}
//使用
User user1 = User.builder().username("user1").password("123").build();Copy after login 7.工具类 @UtilityClass
public class MyUtils{
//会将此方法自动转为静态方法
public void print(String str){
...
}
}
//使用
MyUtils.print("hello");Copy after login 8.自动关闭流 public static void main(String[] args) throws Exception {
//使用Cleanup会自动调用close方法
@Cleanup InputStream in = new FileInputStream(args[0]);
@Cleanup OutputStream out = new FileOutputStream(args[1]);
byte[] b = new byte[1024];
while (true) {
int r = in.read(b);
if (r == -1) break;
out.write(b, 0, r);
}
}Copy after login 9.省略Logger时的初始化 @Log4j
@Log
public class User{
//会自动添加此语句
//Logger logger = Logger.getLogger(User.class);
...
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