android中的文件未找到异常，具有正确的文件路径和权限

Question

我正在尝试阅读已创建的CSV文件。 path变量显示android app文件夹中的正确路径。此外，我已添加读取和写入外部存储权限，但我仍然得到文件未找到异常，如Volley Error toast消息。

阅读CSV代码： -

    String path = String.valueOf(this.getExternalFilesDir(null));
    Log.d("Path",path+"/Final.csv");
    File csvFILE = new File(path+"/","Final.csv");
    try {
        CSVReader csvREAD = new CSVReader(new
                FileReader(path));
        String[] csvLINE;
        int skip = 0;
        try {
            Log.d("I was here","kk");
            while((csvLINE = csvREAD.readNext())!=null)
            {
                if(skip > 0)//becasue first line is column headers
                {
                    String PARAM_DISTRICT = csvLINE[0];
                    String PARAM_TALUKA = csvLINE[1];
                    String PARAM_VILLAGE = csvLINE[2];
                    String PARAM_FARMER_NAME = csvLINE[3];
                    String PARAM_CONTACT_NUMBER = csvLINE[4];
                    String PARAM_GAT_NUMBER = csvLINE[5];
                    String PARAM_CROP_NAME = csvLINE[6];
                    String PARAM_LANDUSE = csvLINE[7];
                    String PARAM_SOIL_TYPE = csvLINE[8];
                    int PARAM_SOIL_DEPTH = Integer.parseInt(csvLINE[9]);
                    double PARAM_LATITUDE = Double.parseDouble(csvLINE[10]);
                    double PARAM_LONGITUDE = Double.parseDouble(csvLINE[11]);
                    String PARAM_TIMESTAMP = csvLINE[12];

                    Data STUD_OBJECT = new Data(PARAM_DISTRICT,PARAM_TALUKA,PARAM_VILLAGE,
                            PARAM_FARMER_NAME,PARAM_CONTACT_NUMBER,PARAM_GAT_NUMBER,
                            PARAM_CROP_NAME,PARAM_LANDUSE,PARAM_SOIL_TYPE,PARAM_SOIL_DEPTH,
                            PARAM_LATITUDE,PARAM_LONGITUDE,PARAM_TIMESTAMP
                    );
                    dataArray.add(STUD_OBJECT);
                }
                else
                {
                    skip ++;
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

    } catch (FileNotFoundException e) {
        Toast.makeText(this, "Volley Error", Toast.LENGTH_SHORT).show();
    }

CSV文件是使用以下代码创建的：

    String Testfile_name="Final";
    Testfile_name=Testfile_name+".csv";
    File logFile = new File(this.getExternalFilesDir(null), Testfile_name);
    if (!logFile.exists())
    {
        try
        {
            logFile.createNewFile();
            String header= "District,Taluka,Village,Farmer_name,Contact_Number,Gat_Number,Crop_name,Landuse,Soil_Type,Soil_Depth,Latitude,Longitude,Timestamp";
            appendLog(header);
        }
        catch (IOException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

Answer 1

这个：

File logFile = new File(this.getExternalFilesDir(null), Testfile_name);

不指向同一个地方：

String path="storage/emulated/0";
Log.d("Path",path+"/Final.csv");
File csvFILE = new File(path+"/","Final.csv");

使它们相同，最好使用第一位代码和getExternalFilesDir()。

Answer 2

问题是您如何访问该文件

String path = String.valueOf(this.getExternalFilesDir(null));

需要改为Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)

检查下面的示例，它的工作原理

AndroidManifest.xml中

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.zackdawood.csvreadwrite">

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <provider
            android:name=".GenericFileProvider"
            android:authorities="${applicationId}.fileprovider"
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/external_files"/>
        </provider>
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

data.Java

package com.zackdawood.csvreadwrite;

public class Data {

    private String PARAM_DISTRICT = "";
    private String PARAM_TALUKA = "";
    private String PARAM_VILLAGE = "";
    private String PARAM_FARMER_NAME = "";
    private String PARAM_CONTACT_NUMBER = "";
    private String PARAM_GAT_NUMBER = "";
    private String PARAM_CROP_NAME = "";
    private String PARAM_LANDUSE = "";
    private String PARAM_SOIL_TYPE = "";
    private String PARAM_TIMESTAMP = "";
    private int PARAM_SOIL_DEPTH = 0;
    private double PARAM_LATITUDE = 0;
    private double PARAM_LONGITUDE = 0;


    public Data(String PARAM_DISTRICT, String PARAM_TALUKA, String PARAM_VILLAGE, String PARAM_FARMER_NAME, String PARAM_CONTACT_NUMBER, String PARAM_GAT_NUMBER, String PARAM_CROP_NAME, String PARAM_LANDUSE, String PARAM_SOIL_TYPE, int PARAM_SOIL_DEPTH, double PARAM_LATITUDE, double PARAM_LONGITUDE, String PARAM_TIMESTAMP) {
        this.PARAM_DISTRICT = PARAM_DISTRICT;
        this.PARAM_TALUKA = PARAM_TALUKA;
        this.PARAM_VILLAGE = PARAM_VILLAGE;
        this.PARAM_FARMER_NAME = PARAM_FARMER_NAME;
        this.PARAM_CONTACT_NUMBER = PARAM_CONTACT_NUMBER;
        this.PARAM_GAT_NUMBER = PARAM_GAT_NUMBER;
        this.PARAM_CROP_NAME = PARAM_CROP_NAME;
        this.PARAM_LANDUSE = PARAM_LANDUSE;
        this.PARAM_SOIL_TYPE = PARAM_SOIL_TYPE;
        this.PARAM_SOIL_DEPTH = PARAM_SOIL_DEPTH;
        this.PARAM_LATITUDE = PARAM_LATITUDE;
        this.PARAM_LONGITUDE = PARAM_LONGITUDE;
        this.PARAM_TIMESTAMP = PARAM_TIMESTAMP;
    }

    @Override
    public String toString() {
        return "Data{" +
                "PARAM_DISTRICT='" + PARAM_DISTRICT + '\'' +
                ", PARAM_TALUKA='" + PARAM_TALUKA + '\'' +
                ", PARAM_VILLAGE='" + PARAM_VILLAGE + '\'' +
                ", PARAM_FARMER_NAME='" + PARAM_FARMER_NAME + '\'' +
                ", PARAM_CONTACT_NUMBER='" + PARAM_CONTACT_NUMBER + '\'' +
                ", PARAM_GAT_NUMBER='" + PARAM_GAT_NUMBER + '\'' +
                ", PARAM_CROP_NAME='" + PARAM_CROP_NAME + '\'' +
                ", PARAM_LANDUSE='" + PARAM_LANDUSE + '\'' +
                ", PARAM_SOIL_TYPE='" + PARAM_SOIL_TYPE + '\'' +
                ", PARAM_TIMESTAMP='" + PARAM_TIMESTAMP + '\'' +
                ", PARAM_SOIL_DEPTH=" + PARAM_SOIL_DEPTH +
                ", PARAM_LATITUDE=" + PARAM_LATITUDE +
                ", PARAM_LONGITUDE=" + PARAM_LONGITUDE +
                '}';
    }

    public String getPARAM_DISTRICT() {
        return PARAM_DISTRICT;
    }

    public void setPARAM_DISTRICT(String PARAM_DISTRICT) {
        this.PARAM_DISTRICT = PARAM_DISTRICT;
    }

    public String getPARAM_TALUKA() {
        return PARAM_TALUKA;
    }

    public void setPARAM_TALUKA(String PARAM_TALUKA) {
        this.PARAM_TALUKA = PARAM_TALUKA;
    }

    public String getPARAM_VILLAGE() {
        return PARAM_VILLAGE;
    }

    public void setPARAM_VILLAGE(String PARAM_VILLAGE) {
        this.PARAM_VILLAGE = PARAM_VILLAGE;
    }

    public String getPARAM_FARMER_NAME() {
        return PARAM_FARMER_NAME;
    }

    public void setPARAM_FARMER_NAME(String PARAM_FARMER_NAME) {
        this.PARAM_FARMER_NAME = PARAM_FARMER_NAME;
    }

    public String getPARAM_CONTACT_NUMBER() {
        return PARAM_CONTACT_NUMBER;
    }

    public void setPARAM_CONTACT_NUMBER(String PARAM_CONTACT_NUMBER) {
        this.PARAM_CONTACT_NUMBER = PARAM_CONTACT_NUMBER;
    }

    public String getPARAM_GAT_NUMBER() {
        return PARAM_GAT_NUMBER;
    }

    public void setPARAM_GAT_NUMBER(String PARAM_GAT_NUMBER) {
        this.PARAM_GAT_NUMBER = PARAM_GAT_NUMBER;
    }

    public String getPARAM_CROP_NAME() {
        return PARAM_CROP_NAME;
    }

    public void setPARAM_CROP_NAME(String PARAM_CROP_NAME) {
        this.PARAM_CROP_NAME = PARAM_CROP_NAME;
    }

    public String getPARAM_LANDUSE() {
        return PARAM_LANDUSE;
    }

    public void setPARAM_LANDUSE(String PARAM_LANDUSE) {
        this.PARAM_LANDUSE = PARAM_LANDUSE;
    }

    public String getPARAM_SOIL_TYPE() {
        return PARAM_SOIL_TYPE;
    }

    public void setPARAM_SOIL_TYPE(String PARAM_SOIL_TYPE) {
        this.PARAM_SOIL_TYPE = PARAM_SOIL_TYPE;
    }

    public int getPARAM_SOIL_DEPTH() {
        return PARAM_SOIL_DEPTH;
    }

    public void setPARAM_SOIL_DEPTH(int PARAM_SOIL_DEPTH) {
        this.PARAM_SOIL_DEPTH = PARAM_SOIL_DEPTH;
    }

    public double getPARAM_LATITUDE() {
        return PARAM_LATITUDE;
    }

    public void setPARAM_LATITUDE(double PARAM_LATITUDE) {
        this.PARAM_LATITUDE = PARAM_LATITUDE;
    }

    public double getPARAM_LONGITUDE() {
        return PARAM_LONGITUDE;
    }

    public void setPARAM_LONGITUDE(double PARAM_LONGITUDE) {
        this.PARAM_LONGITUDE = PARAM_LONGITUDE;
    }

    public String getPARAM_TIMESTAMP() {
        return PARAM_TIMESTAMP;
    }

    public void setPARAM_TIMESTAMP(String PARAM_TIMESTAMP) {
        this.PARAM_TIMESTAMP = PARAM_TIMESTAMP;
    }


}

generic file provider.Java

package com.zackdawood.csvreadwrite;

import android.support.v4.content.FileProvider;

public class GenericFileProvider extends FileProvider {
}

strings.xml中

<resources>
    <string name="app_name">CSVReadWrite</string>
    <string name="write_button">Write CSV</string>
    <string name="read_button">Read CSV</string>
    <string name="request_access">Request Access</string>
</resources>

external_files.xml

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path name="external_files" path="."/>
</paths>

main activity.Java

package com.zackdawood.csvreadwrite;

import android.content.Context;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.FileProvider;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

import com.opencsv.CSVReader;
import com.opencsv.CSVWriter;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private static final String[] PERMISSIONS = {android.Manifest.permission.READ_EXTERNAL_STORAGE, android.Manifest.permission.WRITE_EXTERNAL_STORAGE};

    private static boolean hasPermissions(Context context, String... permissions) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && context != null && permissions != null) {
            for (String permission : permissions) {
                if (ActivityCompat.checkSelfPermission(context, permission) != PackageManager.PERMISSION_GRANTED) {
                    return false;
                }
            }
        }
        return true;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ActivityCompat.requestPermissions(MainActivity.this, PERMISSIONS, 112);
        Log.v(TAG, "onCreate() Method invoked ");

    }

    public void read(View view) {
        File csvFILE = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), "Final.csv");
        Log.d(TAG, csvFILE.getAbsolutePath());
        Uri path = FileProvider.getUriForFile(this, BuildConfig.APPLICATION_ID + ".fileprovider", csvFILE);

        try {
            CSVReader csvREAD = new CSVReader(new
                    FileReader(csvFILE));
            String[] csvLINE;
            int skip = 0;
            try {
                Log.d("I was here", "kk");
                while ((csvLINE = csvREAD.readNext()) != null) {
                    if (skip >= 0)//becasue first line is column headers
                    {
                        String PARAM_DISTRICT = csvLINE[0];
                        String PARAM_TALUKA = csvLINE[1];
                        String PARAM_VILLAGE = csvLINE[2];
                        String PARAM_FARMER_NAME = csvLINE[3];
                        String PARAM_CONTACT_NUMBER = csvLINE[4];
                        String PARAM_GAT_NUMBER = csvLINE[5];
                        String PARAM_CROP_NAME = csvLINE[6];
                        String PARAM_LANDUSE = csvLINE[7];
                        String PARAM_SOIL_TYPE = csvLINE[8];
                        int PARAM_SOIL_DEPTH = Integer.parseInt(csvLINE[9]);
                        double PARAM_LATITUDE = Double.parseDouble(csvLINE[10]);
                        double PARAM_LONGITUDE = Double.parseDouble(csvLINE[11]);
                        String PARAM_TIMESTAMP = csvLINE[12];

                        Data STUD_OBJECT = new Data(PARAM_DISTRICT, PARAM_TALUKA, PARAM_VILLAGE,
                                PARAM_FARMER_NAME, PARAM_CONTACT_NUMBER, PARAM_GAT_NUMBER,
                                PARAM_CROP_NAME, PARAM_LANDUSE, PARAM_SOIL_TYPE, PARAM_SOIL_DEPTH,
                                PARAM_LATITUDE, PARAM_LONGITUDE, PARAM_TIMESTAMP
                        );
                        //dataArray.add(STUD_OBJECT);
                        Toast.makeText(this, STUD_OBJECT.toString(), Toast.LENGTH_LONG).show();

                    } else {
                        skip++;
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
                Log.e(TAG, "read() error" + e.getMessage());
                Log.e(TAG, "read() error" + e.getStackTrace());
            }

        } catch (FileNotFoundException e) {
            Log.e(TAG, "read() error" + e.getMessage());
            Log.e(TAG, "read() error" + e.getStackTrace());
            Toast.makeText(this, "Volley Error", Toast.LENGTH_SHORT).show();
        }
    }

    public void write(View view) {
        String Testfile_name = "Final";
        Testfile_name = Testfile_name + ".csv";
        File logFile = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), Testfile_name);
        if (!logFile.exists()) {
            try {
                logFile.createNewFile();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                Log.e(TAG, "write() error" + e.getMessage());
                Log.e(TAG, "write() error" + e.getStackTrace());
            }
        }


        try {
            String header = "District,Taluka,Village,Farmer_name,Contact_Number,Gat_Number,Crop_name,Landuse,Soil_Type,Soil_Depth,Latitude,Longitude,Timestamp";
            String[] stringList = new String[13];
            stringList[0] = "District";
            stringList[1] = "Taluka";
            stringList[2] = "Village";
            stringList[3] = "Farmer_name";
            stringList[4] = "Contact_Number";
            stringList[5] = "Gat_Number";
            stringList[6] = "Crop_name";
            stringList[7] = "Landuse";
            stringList[8] = "Soil_Type";
            stringList[9] = "1";
            stringList[10] = "2";
            stringList[11] = "2";
            stringList[12] = "2007-11-11 12:13:14";
            FileWriter fw = new FileWriter(logFile);
            CSVWriter writer = new CSVWriter(fw, ',');
            writer.writeNext(stringList);
            writer.close();
            fw.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            Log.e(TAG, "write() error" + e.getMessage());
            Log.e(TAG, "write() error" + e.getStackTrace());
        }


    }

    public void request(View view) {
        ActivityCompat.requestPermissions(MainActivity.this, PERMISSIONS, 112);
    }
}

的build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.zackdawood.csvreadwrite"
        minSdkVersion 15
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation "com.opencsv:opencsv:4.0"
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'


}

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">


    <LinearLayout
        android:layout_width="395dp"
        android:layout_height="715dp"
        android:orientation="vertical"
        tools:layout_editor_absoluteX="8dp"
        tools:layout_editor_absoluteY="8dp">

        <Button
            android:id="@+id/button2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/write_button"
            android:onClick="write"/>

        <Button
            android:id="@+id/button3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/read_button"
            android:onClick="read"/>

        <Button
            android:id="@+id/button4"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/request_access"
            android:onClick="request"/>
    </LinearLayout>
</android.support.constraint.ConstraintLayout>

代码布局

代码输出