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) {}
            }
        }
    }
}