How to lookup port usage and release the port. (Resolve Issue: Port in-use by unknown process)

When we develop web applications, a very common problem is that sometimes we don't know what is using the current port that we need. And we cann't start our server while getting this kind of exception:

First we could look at the Task Manager to see whether we can get the process which is using this port. But what if we got nothing? Kill every suspects? It's dangerous and sometimes doesn't help at all.
Restart the computer? Ohh that'll work, that's also what I did previously but it's so out!!! It's so painful to restart everything and it's really unneccessary.

Now I get one solution, which is very easy and helpful.

For example, I want to user port "8080" but it's in use by unknown process.

First open the cmd, execute => netstat -aon|findstr "8080"
Then you'll get result like this:
  TCP    0.0.0.0:8080           0.0.0.0:0              LISTENING       87460
  TCP    [::]:8080                 [::]:0                    LISTENING       87460

Now we know who is using the port, the process with PID "87460".

Then in the cmd, we execute => taskkill /pid 87460 -f
Then you'll get result like this:
SUCCESS: The process with PID 87460 has been terminated.

That's it! Then you retart the server, everything will be fine.

[MongoDB-Escape dots '.' in map key] Resolve org.springframework.data.mapping.model.MappingException: Map key foo.map.key contains dots but no replacement was configured!

Sometimes we need to save map into MongoDB. But the key of the map cannot have dots inside its keys.

If the key has dot(s), by default we'll get this kind of exception:

org.springframework.data.mapping.model.MappingException: Map key foo.bar.key contains dots but no replacement was configured! Make sure map keys don't contain dots in the first place or configure an appropriate replacement!
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.potentiallyEscapeMapKey(MappingMongoConverter.java:622)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeMapInternal(MappingMongoConverter.java:586)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.createMap(MappingMongoConverter.java:517)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writePropertyInternal(MappingMongoConverter.java:424)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter$3.doWithPersistentProperty(MappingMongoConverter.java:386)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter$3.doWithPersistentProperty(MappingMongoConverter.java:373)
    at org.springframework.data.mapping.model.BasicPersistentEntity.doWithProperties(BasicPersistentEntity.java:257)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeInternal(MappingMongoConverter.java:373)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writePropertyInternal(MappingMongoConverter.java:451)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter$3.doWithPersistentProperty(MappingMongoConverter.java:386)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter$3.doWithPersistentProperty(MappingMongoConverter.java:373)
    at org.springframework.data.mapping.model.BasicPersistentEntity.doWithProperties(BasicPersistentEntity.java:257)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeInternal(MappingMongoConverter.java:373)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writePropertyInternal(MappingMongoConverter.java:451)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter$3.doWithPersistentProperty(MappingMongoConverter.java:386)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter$3.doWithPersistentProperty(MappingMongoConverter.java:373)
    at org.springframework.data.mapping.model.BasicPersistentEntity.doWithProperties(BasicPersistentEntity.java:257)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeInternal(MappingMongoConverter.java:373)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.writeInternal(MappingMongoConverter.java:345)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.write(MappingMongoConverter.java:310)
    at org.springframework.data.mongodb.core.convert.MappingMongoConverter.write(MappingMongoConverter.java:77)
    at org.springframework.data.mongodb.core.MongoTemplate.doSave(MongoTemplate.java:859)
    at org.springframework.data.mongodb.core.MongoTemplate.save(MongoTemplate.java:806)
    at org.springframework.data.mongodb.core.MongoTemplate.save(MongoTemplate.java:794)

Refer to the source code:

Spring => "MappingMongoConverter.java"

/**
     * Potentially replaces dots in the given map key with the configured map key replacement if configured or aborts
     * conversion if none is configured.
     * 
     * @see #setMapKeyDotReplacement(String)
     * @param source
     * @return
     */
    protected String potentiallyEscapeMapKey(String source) {

        if (!source.contains(".")) {
            return source;
        }

        if (mapKeyDotReplacement == null) {
            throw new MappingException(String.format("Map key %s contains dots but no replacement was configured! Make "
                    + "sure map keys don't contain dots in the first place or configure an appropriate replacement!", source));
        }

        return source.replaceAll("\\.", mapKeyDotReplacement);
    }

So the solution is configure the property mapKeyDotReplacement for bean MappingMongoConverter in the spring config file.

For example:

<bean id="mongoMoxydomainConverter" class="org.springframework.data.mongodb.core.convert.MappingMongoConverter">
        <constructor-arg index="0" ref="mongoDbFactory" />
        <constructor-arg index="1">
            <bean class="org.springframework.data.mongodb.core.mapping.MongoMappingContext" />
        </constructor-arg>
        <property name="mapKeyDotReplacement" value="\\+"/>
</bean>

What needs to be mentioned is that, the value that we set for "mapKeyDotReplacement" must follow the regular pattern's rule. If use reserved character, must use '\\' to translate it.

[Date Formatting] Java Default Engine AND Joda framework

A formatting string describes how date/time values should be read and written from(to) string representation

Now we compare the two kinds of formatting engines.

Engine	Formatter Thread-safe?	Description	Example
Java	SimpleDateFormat NO	Standard Java date implementation. Provides lenient, error-prone and full-featured parsing and writing. It has moderate speed and is generally a good choice unless you need to work with large quantities of date/time fields. For advanced study please refer to Java SimpleDateFormat documentation.	yyyy-MM-dd HH:mm:ss
Joda	DateTimeFormat DateTimeFormatter YES	An improved third-party date library. Joda is stricter on input data accuracy when parsing and does not work well with time zones. It does, however, provide a 20-30% speed increase compared to standard Java. For further reading please visit the project site at http://joda-time.sourceforge.net). Joda may be convenient for AS/400 machines. On the other hand, Joda is unable to read time zone expressed with any number of z letters and/or at least three Z letters in a pattern.	yyyy-MM-dd HH:mm:ss

****************************
Java Default:
****************************

1.1 Date Format Pattern Syntax (Java)

Letter	Date or Time Component	Presentation	Examples
G	Era designator	Text	AD
Y	Year	Year	1996; 96
M	Month in year	Month	July; Jul; VII; 07; 7
w	Week in year	Number	27
W	Week in month	Number	2
D	Day in year	Number	189
d	Day in month	Number	10
F	Day of week in month	Number	2
E	Day in week	Text	Tuesday; Tue
a	Am/pm marker	Text	PM
H	Hour in day (0-23)	Number	0
k	Hour in day (1-24)	Number	24
K	Hour in am/pm (0-11)	Number	0
h	Hour in am/pm (1-12)	Number	12
m	Minute in hour	Number	30
s	Second in minute	Number	55
S	Millisecond	Number	970
z	Time zone	General time zone	Pacific Standard Time; PST; GMT-08:00
Z	Time zone	RFC 822 time zone	-0800
'	Escape for text/id	Delimiter	(none)
''	Single quote	Literal	'

The number of symbol letters you specify also determines the format. For example, if the "zz" pattern results in "PDT", then the "zzzz" pattern generates "Pacific Daylight Time". The following table summarizes these rules:

1.2 Rules for Date Format Usage (Java)

Presentation	Processing	Number of Pattern Letters	Form
Text	Formatting	1 - 3	short or abbreviated form, if one exists
Text	Formatting	>= 4	full form
Text	Parsing	>= 1	both forms
Year	Formatting	2	truncated to 2 digits
Year	Formatting	1 or >= 3	interpreted as Number.
Year	Parsing	1	intepreted literally
Year	Parsing	2	interpreted relative to the century within 80 years before or 20 years after the time when theSimpleDateFormat instance is created
Year	Parsing	>= 3	intepreted literally
Month	Both	1-2	interpreted as a Number
Month	Parsing	>= 3	interpreted as Text (using Roman numbers, abbreviated month name - if exists, or full month name)
Month	Formatting	3	interpreted as Text (using Roman numbers, or abbreviated month name - if exists)
Month	Formatting	>= 4	interpreted as Text (full month name)
Number	Formatting	minimum number of required digits	shorter numbers are padded with zeros
Number	Parsing	number of pattern letters is ignored (unless needed to separate two adjacent fields)	any form
General time zone	Both	1-3	short or abbreviated form, if has a name. Otherwise, GMT offset value (GMT[sign][[0]0-23]:[00-59])
General time zone	Both	>= 4	full form, , if has a name. Otherwise, GMT offset value (GMT[sign][[0]0-23]:[00-59])
General time zone	Parsing	>= 1	RFC 822 time zone form is allowed
RFC 822 time zone	Both	>= 1	RFC 822 4-digit time zone format is used ([sign][0-23][00-59])
RFC 822 time zone	Parsing	>= 1	General time zone form is allowed

Examples:

1.3 Date and Time Format Patterns and Results (Java)

Date and Time Pattern	Result
"yyyy.MM.dd G 'at' HH:mm:ss z"	2001.07.04 AD at 12:08:56 PDT
"EEE, MMM d, ''yy"	Wed, Jul 4, '01
"h:mm a"	12:08 PM
"hh 'o''clock' a, zzzz"	12 o'clock PM, Pacific Daylight Time
"K:mm a, z"	0:08 PM, PDT
"yyyyy.MMMMM.dd GGG hh:mm aaa"	02001.July.04 AD 12:08 PM
"EEE, d MMM yyyy HH:mm:ss Z"	Wed, 4 Jul 2001 12:08:56 -0700
"yyMMddHHmmssZ"	010704120856-0700
"yyyy-MM-dd'T'HH:mm:ss.SSSZ"	2001-07-04T12:08:56.235-0700

****************************
JODA:
****************************
2.1 Date Format Pattern Syntax (Joda)

Symbol	Meaning	Presentation	Examples
G	Era designator	Text	AD
C	Century of era (>=0)	Number	20
Y	Year of era (>=0)	Year	1996
y	Year	Year	1996
x	Week of weekyear	Year	1996
M	Month of year	Month	July; Jul; 07
w	Week of year	Number	27
D	Day of year	Number	189
d	Day of month	Number	10
e	Day of week	Number	2
E	Day of week	Text	Tuesday; Tue
a	Halfday of day	Text	PM
H	Hour of day (0-23)	Number	0
k	Clockhour of day (1-24)	Number	24
K	Hour of halfday (0-11)	Number	0
h	Clockhour of halfday (1-12)	Number	12
m	Minute of hour	Number	30
s	Second of minute	Number	55
S	Fraction of second	Number	970
z	Time zone	Text	Pacific Standard Time; PST
Z	Time zone offset/id	Zone	-0800; -08:00; America/Los_Angeles
'	Escape for text/id	Delimiter	(none)
''	Single quote	Literal	'

We can see from above table, although actual format strings for Java and Joda are almost 100% compatible with each other, still there are differences. The 'F' in default java is not supported in Joda.

Basically, 'F' means 'Day of week in month', for example, '2013-11-8' is the second friday in Nov of 2013, so 'F' will get 2 as result. While 'E' means 'Day of week' only, with the same example, '2013-11-8', 'E' will get 5 as result, because it's Friday, the fifth day in the week.

The number of symbol letters you specify also determines the format. The following table summarizes these rules:

2.2 Rules for Date Format Usage (Joda)

Presentation	Processing	Number of Pattern Letters	Form
Text	Formatting	1 - 3	short or abbreviated form, if one exists
Text	Formatting	>= 4	full form
Text	Parsing	>= 1	both forms
Year	Formatting	2	truncated to 2 digits
Year	Formatting	1 or >= 3	interpreted as Number.
Year	Parsing	>= 1	intepreted literally
Month	Both	1-2	interpreted as a Number
Month	Parsing	>= 3	interpreted as Text (using Roman numbers, abbreviated month name - if exists, or full month name)
Month	Formatting	3	interpreted as Text (using Roman numbers, or abbreviated month name - if exists)
Month	Formatting	>= 4	interpreted as Text (full month name)
Number	Formatting	minimum number of required digits	shorter numbers are padded with zeros
Number	Parsing	>= 1	any form
Zone name	Formatting	1-3	short or abbreviated form
Zone name	Formatting	>= 4	full form
Time zone offset/id	Formatting	1	Offset without a colon between hours and minutes
Time zone offset/id	Formatting	2	Offset with a colon between hours and minutes
Time zone offset/id	Formatting	>= 3	Full textual form like this: "Continent/City"
Time zone offset/id	Parsing	1	Offset without a colon between hours and minutes
Time zone offset/id	Parsing	2	Offset with a colon between hours and minutes

For more details, the official docs are the best place to go.

Reference:
Micosoft: StandardDate and Time Format Strings

Joda: User Guide

Java Doc of SimpleDateFormat

One good summarization found on the internet