Countermeasures for Java OutOfMemoryError

Basically, it is necessary to investigate and analyze with gcviewer-1.36 or Memory Analyzer to identify the cause. In my case, I need to save a large object every second, and I get an error in less than an hour.

Countermeasure:

1. Add VM memory (if necessary)

startup_parameters.sh

appserver_mem="6000m"
appserver_java_opt="-Xms=3074m -Xmx=3074m -XX:PermSize=1024m -XX:MaxPermSize=1024m -XX:NewSize=1024m -XX:MaxNewSize=1024m  -server -Djava.awt.headless=true"

2. By flyingweight to the source, in the case of the same String or object, it will be saved in the memory as one.

flyweight core class

FlyweightPool.java

package util;

import java.lang.ref.WeakReference;
import java.util.WeakHashMap;

public class FlyweightPool<T> {

    private WeakHashMap<T, WeakReference<T>> pool = new WeakHashMap<>();
    public FlyweightPool() {}


    public T flyweightOf(T obj) {
        if (obj == null) {
            return null;
        }
        synchronized(pool) {
            WeakReference<T> w = pool.get(obj);
            T flyweihgt = (w == null ? null : w.get());
            if (flyweihgt != null) {
                return flyweihgt;
            }
            pool.put(obj, new WeakReference<T>(obj));
            return obj;
        }
    }

    public boolean contains(T obj) {
        synchronized (pool) {
            return pool.containsKey(obj);
        }
    }

    public void remove(T obj) {
        synchronized (pool) {
            pool.remove(obj);
        }
    }
}

flyweight implementation class

TsunamiBinaryPointBean.java

    private static final FlyweightPool<List<TsunamiBinaryFauldBean>> listFlyweights = new FlyweightPool<>();
    private static final FlyweightPool<TsunamiBinaryFauldBean> dataFlyweight = new FlyweightPool<>();

    /**
     *Set the point ID
     */
	public void setPointID(String pointID){
		this.pointID = StringUtil.flyweightOf(pointID);
	}

    /**
     *Memory tuning, flyweight objects
     */
    public void optimizeMemory() {
        List<TsunamiBinaryFauldBean> fauldBean;
        synchronized(this.tsunamiBinaryFaulds) {
        	TsunamiBinaryFauldBean[] dataArr = new TsunamiBinaryFauldBean[this.tsunamiBinaryFaulds.size()];
            for (int i = 0; i < this.tsunamiBinaryFaulds.size(); i++) {
                dataArr[i] = dataFlyweight.flyweightOf(this.tsunamiBinaryFaulds.get(i));
            }
            fauldBean = listFlyweights.flyweightOf(Arrays.asList(dataArr));
        }
        this.tsunamiBinaryFaulds = fauldBean;
    }

3. Still useless, save it in memory as a compressed binary instead of an object

compression

XXX.java

    public static ByteBuffer compress(ByteBuffer buffer){
        ByteArrayOutputStream compressBaos = new ByteArrayOutputStream();
        GZIPOutputStream gzip = null;
        try{
            gzip = new GZIPOutputStream(compressBaos) {{
                def.setLevel(Deflater.BEST_COMPRESSION);
             }};
            gzip.write(buffer.array());
            gzip.finish();
            gzip.flush();
            compressBaos.flush();
            
            byte[] compressed = compressBaos.toByteArray();
            return ByteBuffer.wrap(compressed);
        }catch(IOException e){
        	DonetLogger.LOGGER.error(1,"ByteBuffer compression", "An error has occurred.", e);
        	return null;
        }finally{
        	try{
        		if(gzip != null){
        			gzip.close();
        		}
        	}catch(Exception e){}
        	try{
        		if(compressBaos != null){
        			compressBaos.close();
        		}
        	}catch(Exception e){}
        	gzip = null;
        	compressBaos = null;
        }
    }

Defrost

XXX.java

public static ByteBuffer decompress(ByteBuffer buffer){
        ByteArrayOutputStream decompressBaos = new ByteArrayOutputStream();
        GZIPInputStream gzip = null;
        byte[] b = new byte[1024*100];
        try{
            gzip = new GZIPInputStream(new ByteArrayInputStream(buffer.array()));
            for (int read = gzip.read(b); read >= 0; read = gzip.read(b)) {
            	decompressBaos.write(b, 0, read);
            }
            decompressBaos.flush();
            byte[] decompressed = decompressBaos.toByteArray();
            return ByteBuffer.wrap(decompressed);
        }catch(IOException e){
        	DonetLogger.LOGGER.error(1,"ByteBuffer decompression", "An error has occurred. Check the accuracy of ByteBuffer.", e);
        	return null;
        }finally{
        	try{
        		if(gzip != null){
        			gzip.close();
        		}
        	}catch(Exception e){}
        	try{
        		if(decompressBaos != null){
        			decompressBaos.close();
        		}
        	}catch(Exception e){}
        	gzip = null;
        	decompressBaos = null;
        }
    }

Binary output

XXX.java

    public void binaryWrite(DataOutputStream output) throws IOException{
    	if(this.getPointCount() <= 0){
    		return;
    	}
		output.writeUTF(this.header);
		output.writeUTF(toSimpleDateTimeString(this.tsunamiDatetime));
		output.writeShort(pointCount);
    	for(TsunamiBinaryPointBean point :tsunamiBinaryPoints){
    		output.writeUTF(point.getAreaID());
    		output.writeUTF(point.getPointID());
    		output.writeFloat(point.getLineAbsAverage());
    		output.writeShort(point.getFauldCount());
    		output.writeFloat(point.getFirstLineAbsAverage());
        	for(int i=0; i<point.getTsunamiBinaryFaulds().length; i++){
        		output.writeUTF(point.getTsunamiBinaryFaulds()[i].getFauldID());
        		output.writeUTF(point.getTsunamiBinaryFaulds()[i].getStartDatetime());
        		output.writeFloat(point.getTsunamiBinaryFaulds()[i].getAmplificationFactor());
        		output.writeFloat(point.getTsunamiBinaryFaulds()[i].getFauldAbsAverageValue());
        	}
    	}
	    output.flush();
    }

Binary reception What is output by DataOutputStream is only received by DataInputStream, and in other cases it becomes an unintended operation.

XXX.java

   public static ByteBuffer toByteBuffer(DataInputStream input){
    	ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    	DataOutputStream out = new DataOutputStream(buffer);
    	byte[] result;
    	try{
	    	out.writeUTF(input.readUTF());
			out.writeUTF(input.readUTF());
			int point = input.readShort();
			out.writeShort(point);
			for(int i=0;i<point;i++){
				out.writeUTF(input.readUTF());
				out.writeUTF(input.readUTF());
				out.writeFloat(input.readFloat());
				int fauld = input.readShort();
				out.writeShort(fauld);
				out.writeFloat(input.readFloat());
				for(int j=0;j<fauld;j++){
					out.writeUTF(input.readUTF());
					out.writeUTF(input.readUTF());
					out.writeFloat(input.readFloat());
					out.writeFloat(input.readFloat());
				}
			}
			result = buffer.toByteArray();
			return ByteBuffer.wrap(result);
		}catch(IOException e){
			return null;
		}finally{
	        try {
	            if (out != null) {
	            	out.close();
	            }
	        }catch (IOException e) {}
	        try {
	            if (buffer != null) {
	            	buffer.close();
	            }
	        }catch (IOException e) {}
	    	buffer = null;
	    	out = null;
		}
    }