[Java知识库]JDK8新的日期类型LocalDate

简介

JDK8以前都是通过java.util.Date与 SimpleDateFormatter格式化时间获得时间，但是这些都不是线程安全的，JDK8带给我们新的获取日期的方式。

实战测试

java.time类简介

Date和time做下区分，Date（日期）的单位是年月日。time（时间）的单位是时分秒

测试

测试代码如下：

import org.junit.FixMethodOrder;
import org.junit.Test;
import org.junit.runners.MethodSorters;
import java.text.SimpleDateFormat;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.util.Date;

/**
 * NAME_ASCENDING 按照名字排序
 */
@FixMethodOrder(MethodSorters.NAME_ASCENDING)
public class DateTest {

    @Test
    public void test01Jdk7DateNow() {
        System.out.println("-------------------test01Jdk7DateNow------------------------");
        Date dateNow = new Date();
        System.out.println("Jdk7获取时间: " + dateNow);
    }

    @Test
    public void test02Jdk8DateNow() {
        System.out.println("\r\n-------------------test02Jdk8DateNow------------------------");
        LocalDate dateNow = LocalDate.now();
        System.out.println("Jdk8获取时间: " + dateNow);
    }

    @Test
    public void test03Jdk7SimpleDateFormat() {
        System.out.println("\r\n-------------------test03Jdk7SimpleDateFormat------------------------");
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date dateNow = new Date();
        String strNow = sdf.format(dateNow);
        System.out.println("SimpleDateFormat格式化后: " + strNow);
    }

    /**
     * DateTimeFormatter 格式化时间
     * 使用"yyyy-MM-dd HH:mm:ss"格式化会报以下异常：
     * java.time.temporal.UnsupportedTemporalTypeException: Unsupported field: HourOfDay
     * 原因：
     * 因为LocalDate中是不包含时分秒的，想要格式化时分秒需要用LocalDateTime这个类，里边包含的有时分秒
     */
    @Test
    public void test04Jdk8DateTimeFormatter() {
        System.out.println("\r\n-------------------test04Jdk8DateTimeFormatter------------------------");
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDate dateNow = LocalDate.now();
        String strNow = dateNow.format(dtf);
        System.out.println("DateTimeFormatter格式化后: " + strNow);
    }

    /**
     * DateTimeFormatter 格式化时间
     * 因为LocalDate中是不包含时分秒的，想要格式化时分秒需要用LocalDateTime这个类，里边包含的有时分秒
     */
    @Test
    public void test05Jdk8LocalDateTime() {
        System.out.println("\r\n-------------------test05Jdk8LocalDateTime------------------------");
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        LocalDateTime dateNow = LocalDateTime.now();
        String strNow = dateNow.format(dtf);
        System.out.println("DateTimeFormatter格式化后: " + strNow);
    }

    /**
     * 时间和字符串之间的转换
     */
    @Test
    public void test06Jdk8String2LocalDate() {
        System.out.println("\r\n-------------------test06Jdk8String2LocalDate------------------------");
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        LocalDateTime dateNow = LocalDateTime.now();
        System.out.println("LocalDateTime(原始): " + dateNow);
        String strNow = dateNow.format(dtf);
        System.out.println("LocalDateTime转String后(格式化后): " + strNow);

        // 将字符串转LocalDateTime
        LocalDateTime str2LocalDateTime = LocalDateTime.parse(strNow, dtf);
        System.out.println("String转LocalDateTime(格式化后): " + str2LocalDateTime);
    }

    /**
     * Date和LocalDateTime之间的转换
     */
    @Test
    public void test07Jdk8Date2LocalDateTime() {
        System.out.println("\r\n-------------------test07Jdk8Date2LocalDateTime------------------------");
        // date转LocalDateTime
        Date date = new Date();
        System.out.println("date转LocalDateTime: " + date.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime());
        // LocalDateTime转date
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println("LocalDateTime转date: " + Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant()));
    }

    /**
     * Timestamp和LocalDateTime之间的转换
     */
    @Test
    public void test08Jdk8Timestamp2LocalDateTime() {
        System.out.println("\r\n-------------------test08Jdk8Timestamp2LocalDateTime------------------------");
        // 或者使用 new Date().getTime()
        long timestamp = System.currentTimeMillis();
        System.out.println("Timestam转换之前：" + timestamp);
        Instant instant1 = Instant.ofEpochMilli(timestamp);
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant1, ZoneId.systemDefault());
        System.out.println("Timestamp转LocalDateTime：" + localDateTime);
        long timestamp1 = localDateTime.toInstant(ZoneOffset.ofHours(8)).toEpochMilli();
        System.out.println("LocalDateTime转Timestamp：" + timestamp1);
    }
}

测试结果如下：

-------------------test01Jdk7DateNow------------------------
Jdk7获取时间: Tue May 10 16:48:50 CST 2022

-------------------test02Jdk8DateNow------------------------
Jdk8获取时间: 2022-05-10

-------------------test03Jdk7SimpleDateFormat------------------------
SimpleDateFormat格式化后: 2022-05-10 16:48:50

-------------------test04Jdk8DateTimeFormatter------------------------
DateTimeFormatter格式化后: 2022-05-10

-------------------test05Jdk8LocalDateTime------------------------
DateTimeFormatter格式化后: 2022-05-10 16:48:50

-------------------test06Jdk8String2LocalDate------------------------
LocalDateTime(原始): 2022-05-10T16:48:50.214
LocalDateTime转String后(格式化后): 2022-05-10 16:48:50
String转LocalDateTime(格式化后): 2022-05-10T16:48:50

-------------------test07Jdk8Date2LocalDateTime------------------------
date转LocalDateTime: 2022-05-10T16:48:50.218
LocalDateTime转date: Tue May 10 16:48:50 CST 2022

-------------------test08Jdk8Timestamp2LocalDateTime------------------------
Timestam转换之前：1652172530220
Timestamp转LocalDateTime：2022-05-10T16:48:50.220
LocalDateTime转Timestamp：1652172530220

其他常用API

其他常用API，遇到了再研究吧

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