Java性能优化实战技巧与最佳实践分享

-Xms4g -Xmx4g -XX:+UseG1GC

-XX:+UseZGC

java -Xms2g -Xmx2g -XX:+UseG1GC -Xlog:gc* MyApp

ExecutorService pool = Executors.newFixedThreadPool(20);

Integer sum = 0;
for (int i = 0; i < 10000; i++) {
    sum += i;  // 自动装箱 + 拆箱
}

int sum = 0;

for (int i = 0; i < 10000; i++) {
    StringBuilder sb = new StringBuilder(); // 频繁创建
}

StringBuilder sb = new StringBuilder();
for (int i = 0; i < 10000; i++) {
    sb.setLength(0);
}

Map<String, Object> map = new HashMap<>(1024);

List<Integer> list = new ArrayList<>();
for (int i = 0; i < 10000; i++) list.add(i);

List<Integer> list = new ArrayList<>(10000);

for (int i : list) {
}

list.stream().forEach(i -> {});

list.parallelStream()....

AtomicInteger counter = new AtomicInteger();

public void increment() {
    counter.incrementAndGet();
}

ExecutorService pool = Executors.newVirtualThreadPerTaskExecutor();

try (FileChannel channel = FileChannel.open(path)) {
    ByteBuffer buffer = ByteBuffer.allocate(8192);
    while (channel.read(buffer) > 0) {
        buffer.flip();
        buffer.clear();
    }
}

for (...) {
    pstmt.executeUpdate();
}

pstmt.addBatch();
pstmt.executeBatch();

HikariConfig config = new HikariConfig();
config.setMaximumPoolSize(20);
config.setConnectionTimeout(3000);
HikariDataSource ds = new HikariDataSource(config);

@Benchmark
public void testAdd() {
    int x = a + b;
}

List<String> results = new ArrayList<>();

for (Item item : items) {
    results.add(item.process());
}

Files.write(path, results);

List<String> results = new ArrayList<>(items.size());

items.parallelStream()          // 利用多核
     .map(Item::process)
     .forEach(results::add);

Files.write(path, results, StandardOpenOption.CREATE);