Android实现png转jpg图片的方法

package com.example.pngtojpgconverter;
 
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
 
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
 
public class MainActivity extends Activity {
    private static final int REQUEST_PICK_PNG = 1001;
    private ImageView imageView;
    private Button btnSelect, btnConvert;
    private Uri selectedUri;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        // 绑定 UI 控件
        imageView = findViewById(R.id.imageView);
        btnSelect = findViewById(R.id.btnSelect);
        btnConvert = findViewById(R.id.btnConvert);
 
        // 选择 PNG 按钮点击
        btnSelect.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 启动系统相册，仅显示 PNG
                Intent intent = new Intent(Intent.ACTION_PICK);
                intent.setType("image/png");
                startActivityForResult(intent, REQUEST_PICK_PNG);
            }
        });
 
        // 转换按钮点击
        btnConvert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 确保已选图片
                if (selectedUri == null) {
                    Toast.makeText(MainActivity.this, "请先选择 PNG 图片", Toast.LENGTH_SHORT).show();
                    return;
                }
                // 调用工具类执行转换
                String jpgPath = ImageConverter.convertPngToJpg(MainActivity.this, selectedUri);
                if (jpgPath != null) {
                    // 转换成功：提示并预览
                    Toast.makeText(MainActivity.this, "转换成功: " + jpgPath, Toast.LENGTH_LONG).show();
                    imageView.setImageURI(Uri.fromFile(new File(jpgPath)));
                } else {
                    // 转换失败：提示
                    Toast.makeText(MainActivity.this, "转换失败", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
 
    // 处理选择结果
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == REQUEST_PICK_PNG && resultCode == RESULT_OK) {
            selectedUri = data.getData();
            imageView.setImageURI(selectedUri);
        }
    }
}
 
// 工具类：执行 PNG 转 JPG
class ImageConverter {
    private static final String TAG = "ImageConverter";
 
    /**
     * 将 PNG 图像转换为 JPG 并保存
     *
     * @param context 应用上下文
     * @param pngUri  PNG 图像的 Uri
     * @return 返回 JPG 文件绝对路径，失败返回 null
     */
    public static String convertPngToJpg(Context context, Uri pngUri) {
        Bitmap srcBitmap = null;
        Bitmap dstBitmap = null;
        FileOutputStream fos = null;
 
        try {
            // 1. 打开 PNG 输入流
            InputStream is = context.getContentResolver().openInputStream(pngUri);
            // 2. 解码为 Bitmap
            srcBitmap = BitmapFactory.decodeStream(is);
            if (srcBitmap == null) {
                Log.e(TAG, "解码 PNG Bitmap 失败");
                return null;
            }
 
            // 3. 创建目标 Bitmap，使用 ARGB_8888 保留高质量
            dstBitmap = Bitmap.createBitmap(
                    srcBitmap.getWidth(),
                    srcBitmap.getHeight(),
                    Bitmap.Config.ARGB_8888
            );
 
            // 4. 使用 Canvas 绘制：白底 + 原图
            Canvas canvas = new Canvas(dstBitmap);
            canvas.drawColor(Color.WHITE); // 填充白色背景
            Paint paint = new Paint();
            paint.setAntiAlias(true);     // 抗锯齿
            canvas.drawBitmap(srcBitmap, 0, 0, paint);
 
            // 5. 准备输出文件
            File outDir = context.getExternalFilesDir("converted");
            if (outDir != null && !outDir.exists()) {
                outDir.mkdirs();
            }
            File jpgFile = new File(outDir, "img_" + System.currentTimeMillis() + ".jpg");
            fos = new FileOutputStream(jpgFile);
 
            // 6. 压缩为 JPG，质量 90%
            boolean ok = dstBitmap.compress(Bitmap.CompressFormat.JPEG, 90, fos);
            fos.flush();
            if (ok) {
                Log.i(TAG, "JPG 保存成功: " + jpgFile.getAbsolutePath());
                return jpgFile.getAbsolutePath();
            } else {
                Log.e(TAG, "Bitmap.compress 返回 false");
                return null;
            }
 
        } catch (IOException e) {
            Log.e(TAG, "转换异常: " + e.getMessage());
            return null;
 
        } finally {
            // 7. 资源释放
            if (srcBitmap != null) srcBitmap.recycle();
            if (dstBitmap != null) dstBitmap.recycle();
            if (fos != null) {
                try { fos.close(); } catch (IOException ignored) {}
            }
        }
    }
}