How to Successfully Reformat Custom Dates from String in Java

Описание: Learn how to convert and reformat date strings in Java easily, avoiding common pitfalls with parsing and formatting.
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This video is based on the question https://stackoverflow.com/q/63756271/ asked by the user 'user9582784' ( https://stackoverflow.com/u/9582784/ ) and on the answer https://stackoverflow.com/a/63756396/ provided by the user 'Konrad Rudolph' ( https://stackoverflow.com/u/1968/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering Date Reformatting in Java

Date manipulation in programming can often be tricky, especially when dealing with string representations of dates. If you’ve ever encountered the message java.text.ParseException: Unparseable date, you're not alone. In this post, we’ll tackle a common problem faced by many Java developers: how to reformat custom dates from a string effectively. We’ll break it down step by step to ensure clarity and understanding.

The Problem

Imagine you have a string date in the format yyyy-MM-dd—for example:

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You want to convert this string into a more readable format—EEE, d MMM yyyy—which would result in something like Sat, 5 Sep 2020. However, if you attempt to parse this string directly into the desired format without the proper steps, you’ll run into the dreaded ParseException. What’s going wrong?

Understanding Parsing vs Formatting

Before diving into the solution, let's clarify the difference between parsing and formatting in Java:

Parsing: This is the process of converting a string into a date object based on a specific format. For example, you need to first recognize that 2020-09-05 is actually in the format yyyy-MM-dd.

Formatting: Once you have a date object, you can then format it into a string representation that follows another specific format, such as EEE, d MMM yyyy.

Step-by-Step Solution

Follow these steps to correctly convert and reformat your date string:

Step 1: Parse the Original String

First, you need to parse your string into a Date object using the correct original format. Here’s the code for this step:

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In this snippet:

We define our date string.

We create a SimpleDateFormat object with the original format (yyyy-MM-dd).

Then we call the parse method to convert the string into a Date object.

Step 2: Format the Date Object

Once you have the Date object, you can format it into your desired format as follows:

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This is where we define our target format and call the format method. Here’s what each part means:

E: Day of the week in short form (e.g., Sat).

d: Day of the month as a single digit for the 1st to 9th (e.g., 5).

MMM: Month in short form (e.g., Sep).

yyyy: Year in four digits.

Step 3: Putting It All Together

Here’s the complete code snippet that combines both steps:

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When you run this program, you'll get Converted Date: Sat, 5 Sep 2020, successfully formatting the string into the desired output.

Wrapping Up

In this guide, we learned how to properly reformat custom date strings in Java by distinguishing between parsing and formatting. Understanding these two processes is essential for effective date manipulation in your applications. Now you can easily convert any date string to your preferred format without running into errors!

Feel free to share your thoughts or any additional questions you might have in the comments below!