android读写sd卡操作写入数据读取数据示例

package com.example.sdcardtest;
import java.io.bufferedreader;
import java.io.file;
import java.io.fileinputstream;
import java.io.filenotfoundexception;
import java.io.ioexception;
import java.io.inputstreamreader;
import java.io.randomaccessfile;

import android.os.bundle;
import android.os.environment;
import android.view.view;
import android.view.view.onclicklistener;
import android.widget.button;
import android.widget.edittext;
import android.app.activity;

public class mainactivity extends activity {
    final string file_name = "/lxp.bin";
    @override
    protected void oncreate(bundle savedinstancestate) {
        super.oncreate(savedinstancestate);
        setcontentview(r.layout.main);
        button write = (button) findviewbyid(r.id.main_btn1);
        button read = (button) findviewbyid(r.id.main_btn2);
        final edittext edit1 = (edittext) findviewbyid(r.id.main_edit1);
        final edittext edit2 = (edittext) findviewbyid(r.id.main_edit2);
        write.setonclicklistener(new onclicklistener() {

            @override
            public void onclick(view v) {
                write(edit1.gettext().tostring().trim());
                edit1.settext("");
            }
        });
        read.setonclicklistener(new onclicklistener() {

            @override
            public void onclick(view v) {
                edit2.settext(read());
            }
        });
    }
    private void write(string content){
        try {
            if(environment.getexternalstoragestate().equals(environment.media_mounted)){
                //获取sd卡的目录
                file sdcarddir = environment.getexternalstoragedirectory();
                file targetfile = new file(sdcarddir.getcanonicalpath() + file_name);
                //以指定文件创建randomaccessfile对象
                randomaccessfile raf = new randomaccessfile(targetfile, "rw");
                //将文件记录指针移动到最后
                raf.seek(targetfile.length());
                //输出文件内容
                raf.write(content.getbytes());
                raf.close();
            }
        } catch (exception e) {
            e.printstacktrace();
        }
    }

    private string read(){
        try {
            if(environment.getexternalstoragestate().equals(environment.media_mounted)){
                //获得sd卡对应的存储目录
                file sdcarddir = environment.getexternalstoragedirectory();
                //获取指定文件对应的输入流
                fileinputstream fis = new fileinputstream(sdcarddir.getcanonicalpath() + file_name);
                //将指定输入流包装成bufferreader
                bufferedreader br = new bufferedreader(new inputstreamreader(fis));
                stringbuilder sb = new stringbuilder("");
                string line = null;
                //循环读取文件内容
                while((line = br.readline()) != null){
                    sb.append(line);
                }
                br.close();
                return sb.tostring();
            }
        } catch (exception e) {
            e.printstacktrace();
        }
        return null;
    }
}

最后别忘了在androidmanafest.xml中增加访问读取sd的权限。