SD卡的数据读取与存储

1.添加对SD卡操作的权限

<!-- 读取SD的权限 -->
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <!-- 写入SD卡的权限 -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

2.布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <EditText
        android:id="@+id/edtext"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20sp" />

    <Button
        android:id="@+id/write"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="write"
        android:text="写入SD卡" />

    <Button
        android:id="@+id/read2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="read2"
        android:text="读取SD卡的文件" />
    <Button
        android:id="@+id/read"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="read"
        android:text="读取系统自带的文件" />

</LinearLayout>

3.Main_Activity.java主程序

package topteam.com.sdkarcunchu_demo;

import android.os.Environment;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;

public class MainActivity extends AppCompatActivity {

    EditText editText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ActionBar bar = getSupportActionBar();
        if (bar != null) {
            bar.hide();
        }
        editText = findViewById(R.id.edtext);
    }

    /**
     * 往SD卡中写入数据
     *
     * @param view
     */
    public void write(View view) {
        //得到SD卡的状态
        String state = Environment.getExternalStorageState();
        //判断sd卡是否可用
        if (state.equals(Environment.MEDIA_MOUNTED)) {
            //得到路径
            File dir = Environment.getExternalStorageDirectory();
            //创建一个文件夹
            File file = new File(dir, "text");
            FileOutputStream fos = null;
            BufferedWriter writer = null;
            String data = editText.getText().toString();
            try {
                fos = new FileOutputStream(file);
                writer = new BufferedWriter(new OutputStreamWriter(fos));
                try {
                    writer.write(data);
                    writer.flush();
                    Toast.makeText(MainActivity.this, "写入完毕", Toast.LENGTH_SHORT).show();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (writer != null) {
                        writer.close();
                    }
                    if (fos != null) {
                        fos.close();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } else {
            Toast.makeText(MainActivity.this, "SD卡不可用", Toast.LENGTH_SHORT).show();
        }
    }

    /**
     * 读取程序自带的文件
     *
     * @param view
     */
    public void read(View view) {
        InputStream in = getResources().openRawResource(R.raw.text);
        BufferedReader br = null;
        try {
            br = new BufferedReader(new InputStreamReader(in, "UTF-8"));
            StringBuilder sb = new StringBuilder();
            String str = "";
            try {
                str = br.readLine();
                while (str != null) {
                    sb.append(str);
                    str = br.readLine();
                }
                editText.setText(sb.toString());
            } catch (IOException e) {
                e.printStackTrace();
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } finally {
            try {
                if (br != null) {
                    br.close();
                }
                if (in != null) {
                    in.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 从sd卡中去读数据
     *
     * @param view
     */
    public void read2(View view) {
        //得到SD卡的状态
        String state = Environment.getExternalStorageState();
        //判断是否可用
        if (state.equals(Environment.MEDIA_MOUNTED)) {
            File dir = Environment.getExternalStorageDirectory();
            File file = new File(dir, "text");
            FileInputStream is = null;
            BufferedReader br = null;
            StringBuilder sb = new StringBuilder();
            String data = "";
            try {
                is = new FileInputStream(file);
                br = new BufferedReader(new InputStreamReader(is));
                try {
                    data = br.readLine();
                    while (data != null) {
                        sb.append(data);
                        data = br.readLine();
                    }
                    editText.setText(sb.toString());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (br != null) {
                        br.close();
                    }
                    if(is!=null){
                        is.close();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } else {
            Toast.makeText(MainActivity.this, "SD卡不可用", Toast.LENGTH_SHORT).show();
        }
    }
}