Android--file Storage Operations (i)
Last Update:2015-12-06
Source: Internet
Author: User
<span id="Label3"></p><p><p>1. Write the built-in space output write</p></p><p><p>2. Write SDcard card input read</p></p><p><p>The file pointer can be read by the Getfilepointer method and set through the Seek Method.</p></p><p><p><span style="color: #ff0000;">Randomaccessfile also integrates FileInputStream and FileOutputStream together,</span> and supports reading or writing data from any byte of a file, and the Randomaccessfile class provides a mechanism for Equivalent to inserting a pointer in the file stream that can be read on demand.</p></p><p><p>File is only an abstraction of a document or directory, can be imagined as a file handle, identity, the class itself only provides open, close, delete, attribute access to the file, and so on;</p></p><p><p>File storage is simply a general javase in the IO stream, just to apply him to the Android phone only;</p></p><p><p><strong>1 File storage</strong></p></p><p><p><strong>The core is the Openfileinput () and Openfileoutput () methods of the Context. then you can read and write with the Java Stream.</strong></p></p><pre> <span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">to save a piece of text to a file:</span></span><span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">The Save () method is called in Ondestory (). This method is written under Super.ondestory ().<br>Openfileoutput</span> --fileoutputstream--outputstreamreader-bufferedreader</span> <span style="color: #0000ff;"><span style="color: #0000ff;"></span> public</span> <span style="color: #0000ff;"><span style="color: #0000ff;">void</span></span><span style="color: #000000;"><span style="color: #000000;">Save () {String data</span></span>=<span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">Data to save</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #000000;"><span style="color: #000000;">; FileOutputStream</span></span><span style="color: #0000ff;"><span style="color: #0000ff;"></span> out</span>=<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span><span style="color: #000000;"><span style="color: #000000;">; BufferedWriter writer</span></span>=<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span><span style="color: #000000;"><span style="color: #000000;">; </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Try</span></span><span style="color: #000000;"><span style="color: #000000;"> { </span></span><span style="color: #0000ff;"><span style="color: #0000ff;"></span> out</span>= Mcontext.openfileoutput (<span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">Data</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span>, context.mode_private);<span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;">a <span style="color: #008000;">filenot error is required.</span></span>writer =<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span>BufferedWriter (<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span>OutputStreamWriter (<span style="color: #0000ff;"><span style="color: #0000ff;"></span> out</span>));<span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">Build a outputstreamwriter. then a bufferedwriter () is Constructed.</span></span>Writer.write (data);<span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">IO error Required</span></span>}<span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(filenotfoundexception E) {e.printstacktrace (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(ioexception E) {e.printstacktrace (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">finally</span></span><span style="color: #000000;"><span style="color: #000000;"> { </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">if</span></span>(writer! =<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span><span style="color: #000000;"><span style="color: #000000;">) { </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Try</span></span><span style="color: #000000;"><span style="color: #000000;">{writer.close (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(ioexception E) {e.printstacktrace (); } } } } </span></span><span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">read data from a file the next time it is opened<br>Openfileinput--fileinputstream--inputstreamreader-bufferedreader<br></span></span>The first two file is always in front of input<span style="color: #0000ff;"><span style="color: #0000ff;"></span> public</span><span style="color: #000000;"><span style="color: #000000;">String load () {fileinputstream</span></span><span style="color: #0000ff;"><span style="color: #0000ff;">inch</span></span>=<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span><span style="color: #000000;"><span style="color: #000000;">; BufferedReader Reader</span></span>=<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span><span style="color: #000000;"><span style="color: #000000;">; StringBuilder SB</span></span>=<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span><span style="color: #000000;"><span style="color: #000000;">StringBuilder (); </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Try</span></span><span style="color: #000000;"><span style="color: #000000;"> { </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">inch</span></span>= Mcontext.openfileinput (<span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">Data</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span>);<span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">Filenot Error Required</span></span>Reader =<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span>BufferedReader (<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span>InputStreamReader (<span style="color: #0000ff;"><span style="color: #0000ff;">inch</span></span><span style="color: #000000;"><span style="color: #000000;">)); String</span> line</span>=<span style="color: #800000;"><span style="color: #800000;">""</span></span><span style="color: #000000;"><span style="color: #000000;">; </span></span><span style="color: #0000ff;"><span style="color: #0000ff;"></span> while</span>(line = Reader.readline ())! =<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span>) {<span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">IO error Required</span></span><span style="color: #000000;"><span style="color: #000000;">Sb.append (line); } } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(filenotfoundexception E) {e.printstacktrace (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(ioexception E) {e.printstacktrace (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">finally</span></span><span style="color: #000000;"><span style="color: #000000;"> { </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">if</span></span>(reader! =<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span><span style="color: #000000;"><span style="color: #000000;">) { </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Try</span></span><span style="color: #000000;"><span style="color: #000000;">{reader.close (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(ioexception E) {e.printstacktrace (); } } } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">return</span></span><span style="color: #000000;"><span style="color: #000000;">sb.tostring (); }</span></span></pre><p><p></p></p><p><p></p></p><p><p></p></p><p><p></p></p><pre><span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">write to built-in storage space</span></span> <span style="color: #0000ff;"><span style="color: #0000ff;"></span> public</span> <span style="color: #0000ff;"><span style="color: #0000ff;">void</span></span><span style="color: #000000;"><span style="color: #000000;">Write (view view) {String inputstring</span></span>=<span style="color: #000000;"><span style="color: #000000;">inputtext.gettext (). toString (); </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">if</span></span>(inputstring = =<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span>||<span style="color: #800000;"><span style="color: #800000;">""</span></span><span style="color: #000000;"><span style="color: #000000;">. Equals (inputstring.trim ())) {toast.maketext (mcontext,</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">Please enter what you want to write, not empty</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #000000;"><span style="color: #000000;">, toast.length_short). show (); </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">return</span></span><span style="color: #000000;"><span style="color: #000000;">; } FileOutputStream Fos</span></span>=<span style="color: #0000ff;"><span style="color: #0000ff;">NULL</span></span><span style="color: #000000;"><span style="color: #000000;">; </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Try</span></span><span style="color: #000000;"><span style="color: #000000;"> { </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">if</span></span><span style="color: #000000;"><span style="color: #000000;">(appendbtn.ischecked ()) {fos</span></span>=<span style="color: #000000;"><span style="color: #000000;">mcontext.openfileoutput (fileName, context.mode_append); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Else</span></span><span style="color: #000000;"><span style="color: #000000;">{fos</span></span>=<span style="color: #000000;"><span style="color: #000000;">mcontext.openfileoutput (fileName, context.mode_private); } fos.write (inputstring.getbytes ()); </span></span><span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">write content to a file</span></span>Toast.maketext (mcontext,<span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;">the <span style="color: #800000;">content is written! </span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #000000;"><span style="color: #000000;">, toast.length_short). show (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(filenotfoundexception e) {toast.maketext (mcontext,</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">File not found, Please check file path</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #000000;"><span style="color: #000000;">, toast.length_short). show (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(ioexception e) {toast.maketext (mcontext,</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">error IO occurred during write</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #000000;"><span style="color: #000000;">, toast.length_short). show (); } } </span></span><span style="color: #008000;"><span style="color: #008000;">//</span></span><span style="color: #008000;"><span style="color: #008000;">read the built-in storage space</span></span> <span style="color: #0000ff;"><span style="color: #0000ff;"></span> public</span> <span style="color: #0000ff;"><span style="color: #0000ff;">void</span></span><span style="color: #000000;"><span style="color: #000000;">Readfromsdcard (view View) {</span></span><span style="color: #0000ff;"><span style="color: #0000ff;">if</span></span><span style="color: #000000;"><span style="color: #000000;">(environment.getexternalstoragestate (). equals (ENVIRONMENT.MEDIA_MOUNTED)) {String path</span></span>= Environment.getexternalstoragedirectory () + file.separator +<span style="color: #000000;"><span style="color: #000000;">fileName; File File</span></span>=<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span><span style="color: #000000;"><span style="color: #000000;">File (path); StringBuilder Sbuilder</span></span>=<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span>StringBuilder (<span style="color: #800000;"><span style="color: #800000;">""</span></span><span style="color: #000000;"><span style="color: #000000;">); </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">byte</span></span>[] buffer =<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span> <span style="color: #0000ff;"><span style="color: #0000ff;">byte</span></span>[<span style="color: #800080;"><span style="color: #800080;"></span> the</span><span style="color: #000000;"><span style="color: #000000;">]; </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">int</span></span>Hasread =<span style="color: #800080;"><span style="color: #800080;">0</span></span><span style="color: #000000;"><span style="color: #000000;">; </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Try</span></span><span style="color: #000000;"><span style="color: #000000;">{randomaccessfile RAF</span></span>=<span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span>Randomaccessfile (file,<span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">RW</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #000000;"><span style="color: #000000;">); </span></span><span style="color: #0000ff;"><span style="color: #0000ff;"></span> while</span>((hasread = Raf.read (buffer))! =-<span style="color: #800080;"><span style="color: #800080;">1</span></span><span style="color: #000000;"><span style="color: #000000;">) {sbuilder.append (</span></span><span style="color: #0000ff;"><span style="color: #0000ff;">New</span></span>String (buffer,<span style="color: #800080;"><span style="color: #800080;">0</span></span><span style="color: #000000;"><span style="color: #000000;">, hasread)); } Outputtext.settext (sbuilder); Raf.close (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(filenotfoundexception e) {toast.maketext (mcontext,</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">File not found, Please check file path</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #000000;"><span style="color: #000000;">, toast.length_short). show (); } </span></span><span style="color: #0000ff;"><span style="color: #0000ff;">Catch</span></span><span style="color: #000000;"><span style="color: #000000;">(ioexception e) {toast.maketext (mcontext,</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #800000;"><span style="color: #800000;">error IO occurred during write</span></span><span style="color: #800000;"><span style="color: #800000;">"</span></span><span style="color: #000000;"><span style="color: #000000;">, toast.length_short). show (); } } }</span></span></pre><p><p></p></p><p><p></p></p><p><p>The default is saved in The/data/data/<packagename>/files/directory.</p></p><p><p>The second is <span style="color: #ff0000;">the operation model of the file</span> , there are two main modes to choose</p></p> <ol> <ol> <li><span style="color: #ff0000;">mode_private</span> (overwrite, is the default mode of Operation)</li> <li><span style="color: #ff0000;">Mode_append</span> (append) does not exist create</li> <li>Mode_world_readable allows other applications to read and write to the Program. but it's too dangerous to be abandoned after 4.2.</li> <li>Mode_world_writeable</li> </ol> </ol><p><p></p></p><p><p><span style="color: #ff0000;">Edit.setselection (inputtext.length ());</span></p></p><p><p><span style="color: #ff0000;">Textutils.isempty () method, which is useful when you can judge both states (null and equal to an empty String) and return True</span></p></p><p><p></p></p><p><p>Android--file Storage Operations (i)</p></p></span>
