详解Java中格式化日期的DateFormat与SimpleDateFormat类
发布时间：2020-05-23 04:45:54 所属栏目：Java 来源：互联网
导读：DateFormat1.DateFormat介绍DateFormat的作用是格式化并解析“日期/时间”。实际上，它是Date的格式化工具，它能帮助我们格式化Date，进而将Date转换成我们想要的String字符串供我们使用
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DateFormat 非构造函数： Object clone() boolean equals(Object object) abstract StringBuffer format(Date date,StringBuffer buffer,FieldPosition field) final StringBuffer format(Object object,FieldPosition field) final String format(Date date) static Locale[] getAvailableLocales() Calendar getCalendar() final static DateFormat getInstance() final static DateFormat getDateInstance() final static DateFormat getDateInstance(int style) final static DateFormat getDateInstance(int style,Locale locale) final static DateFormat getTimeInstance() final static DateFormat getTimeInstance(int style) final static DateFormat getTimeInstance(int style,Locale locale) final static DateFormat getDateTimeInstance() final static DateFormat getDateTimeInstance(int dateStyle,int timeStyle) final static DateFormat getDateTimeInstance(int dateStyle,int timeStyle,Locale locale) NumberFormat getNumberFormat() TimeZone getTimeZone() int hashCode() boolean isLenient() Date parse(String string) abstract Date parse(String string,ParsePosition position) Object parSEObject(String string,ParsePosition position) void setCalendar(Calendar cal) void setLenient(boolean value) void setNumberFormat(NumberFormat format) void setTimeZone(TimeZone timezone) 注意：DateFormat是一个抽象类。 final static DateFormat getInstance() final static DateFormat getTimeInstance() final static DateFormat getTimeInstance(int style) final static DateFormat getTimeInstance(int style,Locale locale) final static DateFormat getDateInstance() final static DateFormat getDateInstance(int style) final static DateFormat getDateInstance(int style,Locale locale) final static DateFormat getDateTimeInstance() final static DateFormat getDateTimeInstance(int dateStyle,int timeStyle) final static DateFormat getDateTimeInstance(int dateStyle,Locale locale) 这些函数在SimpleDateFormat.java中的定义如下：
public static final int FULL = 0;
public static final int LONG = 1;
public static final int MEDIUM = 2;
public static final int SHORT = 3;
public static final int DEFAULT = MEDIUM;
public final static DateFormat getInstance() {
return getDateTimeInstance(SHORT,SHORT);
}
public final static DateFormat getTimeInstance()
{
return get(DEFAULT,1,Locale.getDefault());
}
public final static DateFormat getTimeInstance(int style)
{
return get(style,Locale.getDefault());
}
public final static DateFormat getTimeInstance(int style,Locale aLocale)
{
return get(style,aLocale);
}
public final static DateFormat getDateInstance()
{
return get(0,DEFAULT,2,Locale.getDefault());
}
public final static DateFormat getDateInstance(int style)
{
return get(0,style,Locale.getDefault());
}
public final static DateFormat getDateInstance(int style,Locale aLocale)
{
return get(0,aLocale);
}
public final static DateFormat getDateTimeInstance()
{
return get(DEFAULT,3,Locale.getDefault());
}
public final static DateFormat getDateTimeInstance(int dateStyle,int timeStyle)
{
return get(timeStyle,dateStyle,Locale.getDefault());
}
public final static DateFormat
getDateTimeInstance(int dateStyle,Locale aLocale)
{
return get(timeStyle,aLocale);
}
/**
* 获取DateFormat实例，实际上是返回SimpleDateFormat对象。
*
* timeStyle -- 值可以为“FULL”或“LONG”或“MEDIUM”或“SHORT”
* dateStyle -- 值可以为“FULL”或“LONG”或“MEDIUM”或“SHORT”
* flags -- 值可以为“1”或“2”或“3”。
* 1 表示获取“时间样式”
* 2 表示获取“日期样式”
* 3 表示获取“时间和日期样式”
* loc -- locale对象，表示“区域”
*/
private static DateFormat get(int timeStyle,int dateStyle,int flags,Locale loc) {
if ((flags & 1) != 0) {
if (timeStyle < 0 || timeStyle > 3) {
throw new IllegalArgumentException("Illegal time style " + timeStyle);
}
} else {
timeStyle = -1;
}
if ((flags & 2) != 0) {
if (dateStyle < 0 || dateStyle > 3) {
throw new IllegalArgumentException("Illegal date style " + dateStyle);
}
} else {
dateStyle = -1;
}
try {
// Check whether a provider can provide an implementation that's closer
// to the requested locale than what the Java runtime itself can provide.
LocaleServiceProviderPool pool =
LocaleServiceProviderPool.getPool(DateFormatProvider.class);
if (pool.hasProviders()) {
DateFormat providersInstance = pool.getLocalizedObject(
DateFormatGetter.INSTANCE,loc,timeStyle,flags);
if (providersInstance != null) {
return providersInstance;
}
}
return new SimpleDateFormat(timeStyle,loc);
} catch (MissingResourceException e) {
return new SimpleDateFormat("M/d/yy h:mm a");
}
}
通过上面的代码，我们能够进一步的认识到：DateFormat的作用是格式化Date；帮助我们将Date转换成我们需要的String字符串。DateFormat提供的功能非常有限，它只能支持FULL、LONG、MEDIUM 和 SHORT 这4种格式。而且，我们获取DateFormat实例时，实际上是返回的SimpleDateFormat对象。 2. DateFormat 实例
import java.util.Date;
import java.util.Locale;
import java.text.DateFormat;
import java.text.FieldPosition;
/**
* DateFormat 的API测试程序
*/
public class DateFormatTest {
public static void main(String[] args) {
// 只显示“时间”：调用getTimeInstance()函数
testGetTimeInstance() ;
// 只显示“日期”：调用getDateInstance()函数
testGetDateInstance() ;
// 显示“日期”+“时间”：调用getDateTimeInstance()函数
testGetDateTimeInstance() ;
// 测试format()函数
testFormat();
}
/**
* 测试DateFormat的getTimeInstance()函数
* 它共有3种重载形式：
* (01) getTimeInstance()
* (02) getTimeInstance(int style)
* (03) getTimeInstance(int style,Locale locale)
*
* @author skywang
*/
private static void testGetTimeInstance() {
Date date = new Date();
//Locale locale = new Locale("fr","FR");
Locale locale = new Locale("zh","CN");
// 等价于 DateFormat.getTimeInstance( DateFormat.MEDIUM);
DateFormat short0 = DateFormat.getTimeInstance( );
// 参数是：“时间的显示样式”
DateFormat short1 = DateFormat.getTimeInstance( DateFormat.SHORT);
DateFormat medium1 = DateFormat.getTimeInstance( DateFormat.MEDIUM);
DateFormat long1 = DateFormat.getTimeInstance( DateFormat.LONG);
DateFormat full1 = DateFormat.getTimeInstance( DateFormat.FULL);
// 参数是：“时间的显示样式” 和 “地区”
DateFormat short2 = DateFormat.getTimeInstance( DateFormat.SHORT,locale);
DateFormat medium2 = DateFormat.getTimeInstance( DateFormat.MEDIUM,locale);
DateFormat long2 = DateFormat.getTimeInstance( DateFormat.LONG,locale);
DateFormat full2 = DateFormat.getTimeInstance( DateFormat.FULL,locale);
System.out.println("n----getTimeInstance ----n"
+ "(1.0) Empty Param : " + short0.format(date) +"n"
+ "(2.1) One Param(s) : " + short1.format(date) +"n"
+ "(2.2) One Param(m) : " + medium1.format(date) +"n"
+ "(2.3) One Param(l) : " + long1.format(date) +"n"
+ "(2.4) One Param(f) : " + full1.format(date) +"n"
+ "(3.1) One Param(s,l): " + short2.format(date) +"n"
+ "(3.2) One Param(m,l): " + medium2.format(date) +"n"
+ "(3.3) One Param(l,l): " + long2.format(date) +"n"
+ "(3.4) One Param(f,l): " + full2.format(date) +"n"
);
}
/**
* 测试DateFormat的getDateTimeInstance()函数
* 它共有3种重载形式：
* (01) getDateInstance()
* (02) getDateInstance(int style)
* (03) getDateInstance(int style,Locale locale)
*/
public static void testGetDateTimeInstance() {
Date date = new Date();
Locale locale = new Locale("zh","CN");
// 等价于 DateFormat.getDateTimeInstance( DateFormat.MEDIUM);
DateFormat short0 = DateFormat.getDateTimeInstance( );
DateFormat short1 = DateFormat.getDateTimeInstance( DateFormat.SHORT,DateFormat.SHORT);
DateFormat medium1 = DateFormat.getDateTimeInstance( DateFormat.MEDIUM,DateFormat.MEDIUM);
DateFormat long1 = DateFormat.getDateTimeInstance( DateFormat.LONG,DateFormat.LONG);
DateFormat full1 = DateFormat.getDateTimeInstance( DateFormat.FULL,DateFormat.FULL);
DateFormat short2 = DateFormat.getDateTimeInstance( DateFormat.SHORT,DateFormat.SHORT,locale);
DateFormat medium2 = DateFormat.getDateTimeInstance( DateFormat.MEDIUM,DateFormat.MEDIUM,locale);
DateFormat long2 = DateFormat.getDateTimeInstance( DateFormat.LONG,DateFormat.LONG,locale);
DateFormat full2 = DateFormat.getDateTimeInstance( DateFormat.FULL,DateFormat.FULL,locale);
System.out.println("n----getDateTimeInstance ----n"
+ "(1.0) Empty Param : " + short0.format(date) +"n"
+ "(2.1) One Param(s) : " + short1.format(date) +"n"
+ "(2.2) One Param(m) : " + medium1.format(date) +"n"
+ "(2.3) One Param(l) : " + long1.format(date) +"n"
+ "(2.4) One Param(f) : " + full1.format(date) +"n"
+ "(3.1) One Param(s,l): " + full2.format(date) +"n"
);
}
/**
* 测试DateFormat的getDateInstance()函数
* 它共有3种重载形式：
* (01) getDateTimeInstance()
* (02) getDateTimeInstance(int dateStyle,int timeStyle)
* (03) getDateTimeInstance(int dateStyle,Locale locale)
*/
public static void testGetDateInstance() {
Date date = new Date();
//Locale locale = new Locale("en","US");
Locale locale = new Locale("zh","CN");
// 等价于 DateFormat.getDateInstance( DateFormat.MEDIUM);
DateFormat short0 = DateFormat.getDateInstance( );
DateFormat short1 = DateFormat.getDateInstance( DateFormat.SHORT);
DateFormat medium1 = DateFormat.getDateInstance( DateFormat.MEDIUM);
DateFormat long1 = DateFormat.getDateInstance( DateFormat.LONG);
DateFormat full1 = DateFormat.getDateInstance( DateFormat.FULL);
DateFormat short2 = DateFormat.getDateInstance( DateFormat.SHORT,locale);
DateFormat medium2 = DateFormat.getDateInstance( DateFormat.MEDIUM,locale);
DateFormat long2 = DateFormat.getDateInstance( DateFormat.LONG,locale);
DateFormat full2 = DateFormat.getDateInstance( DateFormat.FULL,locale);
System.out.println("n----getDateInstance ----n"
+ "(1.0) Empty Param : " + short0.format(date) +"n"
+ "(2.1) One Param(s) : " + short1.format(date) +"n"
+ "(2.2) One Param(m) : " + medium1.format(date) +"n"
+ "(2.3) One Param(l) : " + long1.format(date) +"n"
+ "(2.4) One Param(f) : " + full1.format(date) +"n"
+ "(3.1) One Param(s,l): " + full2.format(date) +"n"
);
}
/**
* 测试DateFormat的format()函数
*/
public static void testFormat() {
Date date = new Date();
StringBuffer sb = new StringBuffer();
FieldPosition field = new FieldPosition(DateFormat.YEAR_FIELD);
DateFormat format = DateFormat.getDateTimeInstance();
sb = format.format(date,sb,field);
System.out.println("ntestFormat");
System.out.printf("sb=%sn",sb);
}
}
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