How to change a value of a file using Java IO function

问题

Can anyone help me how to change a line in a file using java IO function. The file is located at SDCard. I have tried some solution from different blog, but failed.

I need to change one attribute wpa_oper_channel=1 to 2,3,4..... as user demand in the file sdcard/sample.txt.

I have also tried using SED command, but still not working. Please suggest if there any solution using java IO function.

The Command I have used using SED :

sed -i 's/wpa_oper_channel=[0-9]\\+/wpa_oper_channel=7/' sample.txt

回答1:

If your configuration file is in the form of a Properties file. This means each line is in a format of key=value. You can easily read, modify and write it. Here is an example, I assume you have no problem with reading and writing a file through streams.

File sdcard = Environment.getExternalStorageDirectory();
File file = new File(sdcard,"sample.txt");
InputStream is = new FileInputStream(file); // Read your existing file
Properties props = new Properties();
props.load(is);
props.setProperty("wpa_oper_channel", "4");
OutputStream out = new FileOutputStream(file); // Your output file stream
prop.store(output, null); // Save your properties file without header

By doing this, you may lose if there is another type of line like comments or else.

Update

I updated to source code. But still you need to get read and write permission.

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

I haven't test the code, It will work with some exception handling. If it is not work please specify your error.

回答2:

You just have to

read the file's content into memory (there are millions of examples on how to do that with java),
change the content (finding the position could be done using e.g. indexOf("wpa_oper_channel="))
write the content back to the file (there are millions of examples for that too)

回答3:

What android do you use?

From android 4.4+ user haven't access to edit and remove files from SD Card. You must copy them to external storage and use there. See this link - http://code.google.com/p/android/issues/detail?id=67570

来源：https://stackoverflow.com/questions/30774066/how-to-change-a-value-of-a-file-using-java-io-function

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java

android

java-io