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[#]: subject: (How Real-World Apps Lose Data)
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[#]: via: (https://theartofmachinery.com/2021/06/06/how_apps_lose_data.html)
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[#]: author: (Simon Arneaud https://theartofmachinery.com)
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[#]: collector: (lujun9972)
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[#]: translator: (PearFL)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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How Real-World Apps Lose Data
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======
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A great thing about modern app development is that there are cloud providers to worry about things like hardware failures or how to set up RAID. Decent cloud providers are extremely unlikely to lose your app’s data, so sometimes I get asked what backups are really for these days. Here are some real-world stories that show exactly what.
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### Story #1
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This first story is from a data science project: it was basically a big, complex pipeline that took data collected from ongoing research and crunched it in various ways to feed some cutting-edge model. The user-facing application hadn’t been launched yet, but a team of data scientists and developers had been working on building the model and its dataset for several months.
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The people working on the project had their own development environments for experimental work. They’d do something like `export ENVIRONMENT=simonsdev` in a terminal, and then all the software running in that terminal would run against that environment instead of the production environment.
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The team was under a lot of pressure to get a user-facing app launched so that stakeholders could actually see some results from their several months of investment. One Saturday, an engineer tried to catch up with some work. He finished an experiment he was doing late in the evening, and decided to tidy up and go home. He fired off a cleanup script to delete everything from his development environment, but strangely it took a lot longer than usual. That’s when he realised he’d lost track of which terminal was configured to point to which environment.
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### Story #2
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Story #2 is from a commercial web and mobile app. The backend had a microservice architecture worked on by a team of engineers. That meant deployments required co-ordination, but things were simplified a bit using a formal release process and automation. New code would get reviewed and merged into master when ready, and every so often a senior developer would tag a release for each microservice, which would then automatically deploy to the staging environment. The releases in the staging environment would periodically get collected together into a meta-release that got signoff from various people (it was a compliance environment) before being automatically deployed to production.
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One day a developer was working on a complex feature, and the other developers working on that microservice agreed that the work-in-progress code should be committed to master with the understanding that it shouldn’t be actually released yet. To cut a long story short, not everyone in the team got the message, and the code got into the release pipeline. Worse, the experimental code required a new way to represent user profile data, so it had an ad-hoc data migration that ran on launch into production and corrupted all user profiles.
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### Story #3
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Story #3 is from another web app. This one had a much simpler architecture: most of the code was in one app, and the data was in a database. However, this app had also been written under a lot of deadline pressure. It turned out that early on in development, when radical database schema changes were common, a feature was added to detect such changes and clean up old data. This was actually useful for early development before launch, and was always meant to be a temporary feature for development environments only. Unfortunately, the code was forgotten about in the rush to build the rest of the app and get to launch. Until, of course, one day it got triggered in the production environment.
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### Postmortem
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With any outage postmortem, it’s easy to lose sight of the big picture and end up blaming everything on some little detail. A special case of that is finding some mistake someone made and then blaming that person. All of the engineers in these stories were actually good engineers (companies that hire SRE consultants aren’t the ones to cut corners with their permanent hires), so firing them and replacing them wouldn’t have solved any problem. Even if you have 100x developers, that 100x is still finite, so mistakes will happen with enough complexity and pressure. The big-picture solution is back ups, which help you however you lose the data (including from malware, which is a hot topic in the news lately). If you’re not okay with having zero copies of it, don’t have one copy.
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Story #1 had a bad end: there were no backups. The project was set back by nearly six months of data collection. By the way, some places only keep a single daily snapshot as a backup, and this story is a good example of how that can go wrong, too: if the data loss happened on Saturday and recovery was attempted on Monday, the one-day backup would only have an empty database from the Sunday.
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Story #2 wasn’t fun, but worked out much better. Backups were available, but the data migration was reversible, too. The unfun part was that the release was done just before lunch and the fix had to be coded up while the production site was down. The main reason I’m telling this story is as a reminder that backups aren’t just about catastrophic data loss. Partial data corruption happens, too, and can be extra messy.
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Story #3 was so-so. A small amount of data was lost permanently, but most was recovered from the backup. Everyone on the team felt pretty bad about not flagging the now-extremely-obviously-dangerous code. I wasn’t involved in the early development, but I felt bad because the recovery took a lot longer than it should have. With a well-tested recovery process, I think the site should have been back online in under 15mins total. But the recovery didn’t work first time, and I had to debug why not and retry. When a production site is down and it’s on you to get it up again, every 10s feels like an eternity. Thankfully, the stakeholders were much more understanding than some. They were actually relieved that a one-off disaster that could have sunk the company only resulted in minutes of lost data and under an hour of downtime.
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It’s extremely common in practice for the backup to “work” but the recovery to fail. Often the recovery works when tested on small datasets, but fails on production-sized datasets. Disaster is most likely to strike when everyone is stressed out, and having the production site down only increases the pressure. It’s a really good idea to test and document the full recovery process while times are good.
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--------------------------------------------------------------------------------
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via: https://theartofmachinery.com/2021/06/06/how_apps_lose_data.html
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作者：[Simon Arneaud][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://theartofmachinery.com
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[b]: https://github.com/lujun9972
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@ -1,163 +0,0 @@
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[#]: subject: (Programming 101: Input and output with Java)
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[#]: via: (https://opensource.com/article/21/3/io-java)
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[#]: author: (Seth Kenlon https://opensource.com/users/seth)
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[#]: collector: (lujun9972)
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[#]: translator: (piaoshi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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Programming 101: Input and output with Java
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======
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Learn how Java handles reading and writing data.
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![Coffee beans and a cup of coffee][1]
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When you write a program, your application may need to read from and write to files stored on the user's computer. This is common in situations when you want to load or store configuration options, you need to create log files, or your user wants to save work for later. Every language handles this task a little differently. This article demonstrates how to handle data files with Java.
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### Installing Java
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Regardless of your computer's platform, you can install Java from [AdoptOpenJDK][2]. This site offers safe and open source builds of Java. On Linux, you may also find AdoptOpenJDK builds in your software repository.
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I recommend using the latest long-term support (LTS) release. The latest non-LTS release is best for developers looking to try the latest Java features, but it likely outpaces what most users have installed—either by default on their system or installed previously for some other Java application. Using the LTS release ensures you're up-to-date with what most users have installed.
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Once you have Java installed, open your favorite text editor and get ready to code. You might also want to investigate an [integrated development environment for Java][3]. BlueJ is ideal for new programmers, while Eclipse and Netbeans are nice for intermediate and experienced coders.
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### Reading a file with Java
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Java uses the `File` library to load files.
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This example creates a class called `Ingest` to read data from a file. When you open a file in Java, you create a `Scanner` object, which scans the file you provide, line by line. In fact, a `Scanner` is the same concept as a cursor in a text editor, and you can control that "cursor" for reading and writing with `Scanner` methods like `nextLine`:
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```
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import java.io.File;
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import java.util.Scanner;
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import java.io.FileNotFoundException;
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public class Ingest {
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public static void main([String][4][] args) {
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try {
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[File][5] myFile = new [File][5]("example.txt");
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Scanner myScanner = new Scanner(myFile);
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while (myScanner.hasNextLine()) {
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[String][4] line = myScanner.nextLine();
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[System][6].out.println(line);
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}
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myScanner.close();
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} catch ([FileNotFoundException][7] ex) {
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ex.printStackTrace();
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} //try
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} //main
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} //class
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```
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This code creates the variable `myfile` under the assumption that a file named `example.txt` exists. If that file does not exist, Java "throws an exception" (this means it found an error in what you attempted to do and says so), which is "caught" by the very specific `FileNotFoundException` library. The fact that there's a library specific to this exact error betrays how common this error is.
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Next, it creates a `Scanner` and loads the file into it. I call it `myScanner` to differentiate it from its generic class template. A `while` loop sends `myScanner` over the file, line by line, for as long as there _is_ a next line. That's what the `hasNextLine` method does: it detects whether there's any data after the "cursor." You can simulate this by opening a file in a text editor: Your cursor starts at the very beginning of the file, and you can use the keyboard to scan through the file with the cursor until you run out of lines.
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The `while` loop creates a variable `line` and assigns it the data of the current line. Then it prints the contents of `line` just to provide feedback. A more useful program would probably parse each line to extract whatever important data it contains.
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At the end of the process, the `myScanner` object closes.
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### Running the code
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Save your code as `Ingest.java` (it's a Java convention to give classes an initial capital letter and name the file to match). If you try to run this simple application, you will probably receive an error because there is no `example.txt` for the application to load yet:
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```
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$ java ./Ingest.java
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java.io.[FileNotFoundException][7]:
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example.txt (No such file or directory)
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```
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What a perfect opportunity to write a Java application that writes data to a file!
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### Writing data to a file with Java
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Whether you're storing data that your user creates with your application or just metadata about what a user did in an application (for instance, game saves or recent songs played), there are lots of good reasons to store data for later use. In Java, this is achieved through the `FileWriter` library, this time by opening a file, writing data into it, and then closing the file:
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```
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import java.io.FileWriter;
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import java.io.IOException;
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public class Exgest {
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public static void main([String][4][] args) {
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try {
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[FileWriter][8] myFileWriter = new [FileWriter][8]("example.txt", true);
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myFileWriter.write("Hello world\n");
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myFileWriter.close();
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} catch ([IOException][9] ex) {
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[System][6].out.println(ex);
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} // try
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} // main
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}
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```
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The logic and flow of this class are similar to reading a file. Instead of a `Scanner`, it creates a `FileWriter` object with the name of a file. The `true` flag at the end of the `FileWriter` statement tells `FileWriter` to _append_ text to the end of the file. To overwrite a file's contents, remove the `true`:
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```
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`FileWriter myFileWriter = new FileWriter("example.txt", true);`
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```
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Because I'm writing plain text into a file, I added my own newline character (`\n`) at the end of the data (`Hello world`) written into the file.
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### Trying the code
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Save this code as `Exgest.java`, following the Java convention of naming the file to match the class name.
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Now that you have the means to create and read data with Java, you can try your new applications, in reverse order:
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```
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$ java ./Exgest.java
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$ java ./Ingest.java
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Hello world
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$
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```
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Because it appends data to the end, you can repeat your application to write data as many times as you want to add more data to your file:
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```
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$ java ./Exgest.java
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$ java ./Exgest.java
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$ java ./Exgest.java
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$ java ./Ingest.java
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Hello world
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Hello world
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Hello world
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$
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```
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### Java and data
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You're don't write raw text into a file very often; in the real world, you probably use an additional library to write a specific format instead. For instance, you might use an XML library to write complex data, an INI or YAML library to write configuration files, or any number of specialized libraries to write binary formats like images or audio.
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For full information, refer to the [OpenJDK documentation][10].
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/3/io-java
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作者：[Seth Kenlon][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
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|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
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[a]: https://opensource.com/users/seth
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/java-coffee-mug.jpg?itok=Bj6rQo8r (Coffee beans and a cup of coffee)
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[2]: https://adoptopenjdk.net
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[3]: https://opensource.com/article/20/7/ide-java
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[4]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+string
|
||||
[5]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+file
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[6]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+system
|
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[7]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+filenotfoundexception
|
||||
[8]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+filewriter
|
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[9]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+ioexception
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[10]: https://access.redhat.com/documentation/en-us/openjdk/11/
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56
translated/talk/20210606 How Real-World Apps Lose Data.md
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56
translated/talk/20210606 How Real-World Apps Lose Data.md
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@ -0,0 +1,56 @@
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[#]: subject: (How Real-World Apps Lose Data)
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[#]: via: (https://theartofmachinery.com/2021/06/06/how_apps_lose_data.html)
|
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[#]: author: (Simon Arneaud https://theartofmachinery.com)
|
||||
[#]: collector: (lujun9972)
|
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[#]: translator: (PearFL)
|
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[#]: reviewer: ( )
|
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[#]: publisher: ( )
|
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[#]: url: ( )
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|
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真实世界的应用程序是如何丢失数据？
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======
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现代应用程序开发的一大优点是，云提供商会担心硬件故障或如何设置RAID等问题。优秀的云供应商不太可能丢失你的应用数据, 所以有时我会被询问现在的备份究竟是什么呢？下面是一些现实世界的故事。
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### 故事 #1
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第一个故事来自一个数据科学项目：它基本上是一个从正在进行的研究中来收集数据的庞大而复杂的管道，然后用各种不同的方式处理以满足一些尖端模型的需要。这个面向用户的应用程序还没有启动，但是一个由数据科学家和开发人员组成的团队已经为建立这个模型和它的数据集工作了好几个月。
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在项目中工作的人有他们自己的实验工作的开发环境。他们会在终端中做一些类似' export ENVIRONMENT=simonsdev '的事情，然后所有在终端上运行的软件都会在那个环境下运行，而不是在生产环境下。
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该团队需要承受着巨大的压力去推出面向用户的应用程序，以便利益相关者能够从他们几个月的投资中真正看到一些回报。一个星期六，一位工程师试图赶完一些工作。他在晚上很晚的时候做完了一个实验，决定收拾东西回家。他启动了一个清理脚本来删除他的开发环境中的所有内容，但奇怪的是，这比平时花费了更长的时间。那时他意识到他已经忘记了哪个终端被配置为指向哪个环境。
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### 故事 #2
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第二个故事来自于一个商业网页和手机应用。后端有一个由一组工程师负责的微服务体系结构。这意味着部署需要协调，但是使用正式的发布过程和自动化简化了一些。新代码在准备好后会被审查并合并到 master 中，并且高级开发人员经常会为每个微服务标记一个版本，然后自动部署到暂存环境。临时环境中的版本会定期收集到一个元版本中，在自动部署到生产之前，该版本会得到不同人的认可（这是一个合规环境）。
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||||
|
||||
有一天，一位开发人员正在开发一个复杂的功能，而其他开发该微服务的开发人员一致认为，应该致力于掌握正在进行的代码，并理解它不应该被实际发布。长话短说，并不是团队中的每个人都收到了消息，而是代码进入了发布管道。更糟糕的是，实验代码需要一种新的方式来表示用户配置文件数据，因此它有一个临时数据迁移，在启动到生产时运行并损坏所有用户配置文件。
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||||
|
||||
### 故事 #3
|
||||
|
||||
第三个故事来自另一款网络应用。这个有一个更简单的架构：大部分代码在一个应用程序中，数据在数据库中。然而，这个应用程序也是在很大的截止日期压力下编写的。事实证明，在开发初期，当彻底的数据库架构更改很常见时，添加了一项功能来检测此类更改并清理旧数据。这实际上对发布前的早期开发很有用，并且始终仅作为开发环境的临时功能。不幸的是，在匆忙构建应用的其余部分并启动时，我们忘记了代码。当然，直到有一天它在生产环境中被触发。
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|
||||
### 事后分析
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||||
|
||||
对于任何停机问题的事后分析，很容易忽视大局，最终将一切归咎于一些小细节。一个特例是发现某人犯了一些错误，然后责怪那个人。这些故事中的所有工程师实际上都是优秀的工程师（雇佣SRE顾问的公司不是为了偷工减料），所以解雇他们，换掉他们并不能解决任何问题。即使你拥有100个开发人员，这100个开发人员仍然是有限的，所以在足够的复杂性和压力下，错误也会发生。最重要的解决方案是备份，它可以帮助你在丢失数据的情况下(包括来自恶意软件的数据，这是最近新闻中的一个热门话题)。如果你无法容忍零拷贝，就不要只有一个副本。
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|
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故事1的结局很糟糕：没有备份。该项目因近六个月的数据收集而推迟。顺便说一句，有些地方只保留一个每日快照作为备份，这个故事也是一个很好的例子，说明了这是如何出错的：如果数据丢失发生在星期六，并且准备在星期一尝试恢复，那么一日备份就只能得到星期日的空数据。
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故事2并不有趣，但效果要好得多。备份可用，但数据迁移也是可逆的。不有趣的部分是发布是在午餐前完成的，并且必须在生产站点关闭时对修复进行编码。我讲这个故事的主要原因是为了提醒大家，备份并不仅仅是灾难性的数据丢失。部分数据损坏也会发生，而且可能会更加混乱。
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|
||||
故事3仅仅只是一般。尽管少量数据永久丢失，但大部分数据可以从备份中恢复。团队中的每个人都对现在没有注释的极其危险的代码感到非常糟糕。我没有参与早期的开发，但我感觉很糟糕，因为恢复数据所需的时间比正常情况要长得多。通过经过良好测试的恢复过程，我认为该站点应该在总共不到 15 分钟的时间内重新上线。但是第一次恢复没有成功，我不得不调试为什么不能成功，然后重试。当一个生产站点宕机了，需要你重新启动它，每10秒就会感觉很漫长。 值得庆幸的是，涉众比某些人理解得多。他们实际上松了一口气，因为一次数分钟的数据丢失和不到一小时的停机时间本就可以使公司陷入瘫痪的灾难。
|
||||
|
||||
在实践中，进行了备份“工作”但恢复失败是非常常见的。很多时候，小型数据集上进行恢复测试是可以正常工作的，但在生产规模的大数据集上就会失败。当每个人都压力过大时，灾难最有可能发生，而关闭生产站点只会增加压力。在时间合适的时候测试和记录完整的恢复过程是一个非常好的主意。
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://theartofmachinery.com/2021/06/06/how_apps_lose_data.html
|
||||
|
||||
作者：[Simon Arneaud][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[PearFL](https://github.com/PearFL)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://theartofmachinery.com
|
||||
[b]: https://github.com/lujun9972
|
||||
@ -0,0 +1,163 @@
|
||||
[#]: subject: (Programming 101: Input and output with Java)
|
||||
[#]: via: (https://opensource.com/article/21/3/io-java)
|
||||
[#]: author: (Seth Kenlon https://opensource.com/users/seth)
|
||||
[#]: collector: (lujun9972)
|
||||
[#]: translator: (piaoshi)
|
||||
[#]: reviewer: ( )
|
||||
[#]: publisher: ( )
|
||||
[#]: url: ( )
|
||||
|
||||
编程秘笈：Java 中的输入和输出
|
||||
======
|
||||
学习 Java 如何外理数据的读与写
|
||||
![Coffee beans and a cup of coffee][1]
|
||||
|
||||
当你写一个程序时，你的应用程序可能需要读取和写入存储在用户计算机上的文件。这在你想加载或存储配置选项，你需要创建日志文件，或你的用户想要保存工作以待后用的情况下是很常见的。每种语言处理这项任务的方式都有所不同。本文演示了如何用 Java 处理数据文件。
|
||||
|
||||
### 安装 Java
|
||||
|
||||
不管你的计算机是什么平台，你都可以从 [AdoptOpenJDK][2] 安装 Java。这个网站提供安全和开源的 Java 构建。在 Linux 上，你的软件库中也可能找到 AdvertOpenJDK 的构建。
|
||||
|
||||
我建议你使用最新的长期支持（LTS）版本。最新的非 LTS 版本对希望尝试最新 Java 功能的开发者来说是最好的，但它很可能超过大多数用户所安装的版本——要么是系统上默认安装的，要么是以前为其他 Java 应用安装的。使用 LTS 版本可以确保你与大多数用户所安装的版本保持一致。
|
||||
|
||||
一旦你安装好了 Java，就可以打开你最喜欢的文本编辑器并准备开始写代码了。你可能还想要研究一下 [Java 集成开发环境][3]。BlueJ 是新程序员的理想选择，而 Eclipse 和 Netbeans 对中级和有经验的编码者更友好。
|
||||
|
||||
### 利用 Java 读取文件
|
||||
|
||||
Java 使用 `File` 类来加载文件。
|
||||
|
||||
这个例子创建了一个叫 `Ingest` 的类来读取文件中数据。当你要在 Java 中打开一个文件时，你创建了一个 `Scanner` 对象，它可以逐行扫描你提供的文件。事实上，`Scanner` 与文本编辑器中的光标是相同的概念，这样你可以用 `Scanner` 的一些方法（如 `nextLine`）来控制这个“光标”以进行读写。
|
||||
|
||||
|
||||
```
|
||||
import java.io.File;
|
||||
import java.util.Scanner;
|
||||
import java.io.FileNotFoundException;
|
||||
|
||||
public class Ingest {
|
||||
public static void main([String][4][] args) {
|
||||
|
||||
try {
|
||||
[File][5] myFile = new [File][5]("example.txt");
|
||||
Scanner myScanner = new Scanner(myFile);
|
||||
while (myScanner.hasNextLine()) {
|
||||
[String][4] line = myScanner.nextLine();
|
||||
[System][6].out.println(line);
|
||||
}
|
||||
myScanner.close();
|
||||
} catch ([FileNotFoundException][7] ex) {
|
||||
ex.printStackTrace();
|
||||
} //try
|
||||
} //main
|
||||
} //class
|
||||
```
|
||||
|
||||
这段代码首先在假设存在一个名为 `example.txt` 的文件的情况下创建了变量 `myfile`。如果该文件不存在，Java 就会“抛出一个异常”（这意味着它在你试图做的事情中发现了一个错误，并这样告诉你），这个异常是被非常明确的 `FileNotFoundException` 类所“捕获”。事实上，有一个专门的类来处理这个明确的错误，这说明这个错误是多么常见。
|
||||
|
||||
接下来，它创建了一个 `Scanner` 并将文件加载到其中。我把它叫做 `myScanner`，以区别于它的通用类模板。接着，一个 `while` 循环将 `myScanner` 逐行送入文件中，只要_存在_下一行。这就是 `hasNextLine` 方法的作用：它检测“光标”之后是否还有数据。你可以通过在文本编辑器中打开一个文件来模拟这个过程：你的光标从文件的第一行开始，你可以用键盘控制光标来向下扫描文件，直到你用完了所有的行。
|
||||
|
||||
`while` 循环创建了一个变量 `line`，并将文件当前行的数据分配给它。然后将 `line` 的内容打印出来以提供反馈。一个更有用的程序可能会解析每一行的内容，从而提取它所包含的任何重要数据。
|
||||
|
||||
在这个过程结束时，关闭 `myScanner` 对象。
|
||||
|
||||
### 运行代码
|
||||
|
||||
将你的代码保存到 `Ingest.java` 文件（这是一个 Java 惯例，将类名的首字母大写，并以类名来命名相应的文件）。如果你试图运行这个简单的应用程序，你可能会接收到一个错误信息，这是因为还没有 `example.txt` 文件供应用程序加载:
|
||||
|
||||
|
||||
```
|
||||
$ java ./Ingest.java
|
||||
java.io.[FileNotFoundException][7]:
|
||||
example.txt (No such file or directory)
|
||||
```
|
||||
|
||||
正好可以编写一个将数据写入文件的 Java 应用程序，多么完美的时机!
|
||||
|
||||
### 利用 Java 将数据写入文件
|
||||
|
||||
无论你是存储用户使用你的应用程序创建的数据，还是仅仅存储关于用户在应用程序中做了什么的元数据（例如，游戏保存或最近播放的歌曲），有很多很好的理由来存储数据供以后使用。在 Java 中，这是通过 `FileWriter` 类实现的，这次先打开一个文件，向其中写入数据，然后关闭该文件。
|
||||
|
||||
|
||||
```
|
||||
import java.io.FileWriter;
|
||||
import java.io.IOException;
|
||||
|
||||
public class Exgest {
|
||||
public static void main([String][4][] args) {
|
||||
try {
|
||||
[FileWriter][8] myFileWriter = new [FileWriter][8]("example.txt", true);
|
||||
myFileWriter.write("Hello world\n");
|
||||
myFileWriter.close();
|
||||
} catch ([IOException][9] ex) {
|
||||
[System][6].out.println(ex);
|
||||
} // try
|
||||
} // main
|
||||
}
|
||||
```
|
||||
|
||||
这个类的逻辑和流程与读取文件类似。但它不是一个 `Scanner`，而是以一个文件的名字为参数创建的一个 `FileWriter` 对象。`FileWriter` 语句末尾的 `true` 标志告诉 `FileWriter` 将文本_追加_到文件的末尾。要覆盖一个文件的内容，请移除 `true` 标志。
|
||||
|
||||
|
||||
```
|
||||
`FileWriter myFileWriter = new FileWriter("example.txt", true);`
|
||||
```
|
||||
|
||||
因为我在向文件中写入纯文本，所以我在写入文件的数据（Hello world）的结尾处手动添加了换行符（\n）。
|
||||
|
||||
### 试试代码
|
||||
|
||||
将这段代码保存到 `Exgest.java` 文件，遵循 Java 的惯例，使文件名为与类名相匹配。
|
||||
|
||||
既然你已经掌握了用 Java 创建和读取数据的方法，你可以按相反的顺序尝试运行你的新应用程序。
|
||||
|
||||
|
||||
```
|
||||
$ java ./Exgest.java
|
||||
$ java ./Ingest.java
|
||||
Hello world
|
||||
$
|
||||
```
|
||||
|
||||
因为程序是把数据追加到文件末尾，所以你可以重复执行你的应用程序以多次写入数据，只要你想把更多的数据添加到你的文件中。
|
||||
|
||||
|
||||
```
|
||||
$ java ./Exgest.java
|
||||
$ java ./Exgest.java
|
||||
$ java ./Exgest.java
|
||||
$ java ./Ingest.java
|
||||
Hello world
|
||||
Hello world
|
||||
Hello world
|
||||
$
|
||||
```
|
||||
|
||||
### Java 和数据
|
||||
|
||||
你并不经常向文件中写入原始文本；实事上，你可能会使用一个其它的类库以写入特定的格式。例如，你可能使用 XML 类库来写复杂的数据，使用 INI 或 YAML 类库来写配置文件，或者使用任何数量的专门类库来写二进制格式，如图像或音频。
|
||||
|
||||
更完整的信息，请参阅 [OpenJDK 文档][10]。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/21/3/io-java
|
||||
|
||||
作者：[Seth Kenlon][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[piaoshi](https://github.com/piaoshi)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/seth
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/java-coffee-mug.jpg?itok=Bj6rQo8r (Coffee beans and a cup of coffee)
|
||||
[2]: https://adoptopenjdk.net
|
||||
[3]: https://opensource.com/article/20/7/ide-java
|
||||
[4]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+string
|
||||
[5]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+file
|
||||
[6]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+system
|
||||
[7]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+filenotfoundexception
|
||||
[8]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+filewriter
|
||||
[9]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+ioexception
|
||||
[10]: https://access.redhat.com/documentation/en-us/openjdk/11/
|
||||
Loading…
Reference in New Issue
Block a user