java - 无法初始化类

Question

我正在编写一个依赖于数据库的 webapp

我尝试检查如果许多用户尝试同时注册会发生什么我正在使用 Gson 从数据库中获取对象

如果我一次注册 50 个用户(通过生成新线程)，一切都很好但是如果我尝试注册 100 个或更多，我会得到 2 个异常，一个说我打开了太多连接，另一个说加载 gson 类失败

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"
at sun.reflect.GeneratedConstructorAccessor13.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.Util.getInstance(Util.java:386)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1014)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:988)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:974)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1110)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2465)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2498)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2283)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:822)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.GeneratedConstructorAccessor1.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:404)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:317)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at com.database.Database.openDatabase(Database.java:229)
at com.database.Database.log(Database.java:253)
at com.electronicarena.utils.Log.debug(Log.java:54)
at com.electronicarena.utils.Log.info(Log.java:68)
at com.database.Database.findAll(Database.java:434)
at com.database.Database.find(Database.java:490)
at com.database.Database.find(Database.java:514)
at com.database.adapters.UserAdapter.getUserByLoginName(UserAdapter.java:53)
at com.database.adapters.UserAdapter.isUserExist(UserAdapter.java:41)
at com.database.adapters.UserAdapter.register(UserAdapter.java:173)
at com.lenabru.webservice.ElectronicArenaWebService.memberRegister(ElectronicArenaWebService.java:65)
at test.UserAdapterTest$UserThread.run(UserAdapterTest.java:168)



Exception in thread "Thread-87" java.lang.NoClassDefFoundError: Could not initialize class com.electronicarena.utils.EAGson
at com.database.DatabaseObject.get(DatabaseObject.java:299)
at com.database.DatabaseObject.set(DatabaseObject.java:365)
at com.database.DatabaseObject.set(DatabaseObject.java:337)
at com.database.DatabaseObject.getFindByKeysPreparedStatement(DatabaseObject.java:97)
at com.database.Database.findAll(Database.java:435)
at com.database.Database.find(Database.java:490)
at com.database.Database.find(Database.java:514)
at com.database.adapters.UserAdapter.getUserByLoginName(UserAdapter.java:53)
at com.database.adapters.UserAdapter.isUserExist(UserAdapter.java:41)
at com.database.adapters.UserAdapter.register(UserAdapter.java:173)
at com.lenabru.webservice.ElectronicArenaWebService.memberRegister(ElectronicArenaWebService.java:65)
at test.UserAdapterTest$UserThread.run(UserAdapterTest.java:168)

---

这是我将用户插入数据库的代码

public int insert(DatabaseObject object) {
    int dbEntry = -1;
    Connection con = null;
    PreparedStatement statement = null;
    String sql = null;
    try {
        Log.info("inserting object: " + object);
        con = openDatabase();
        statement = object.getInsertPreparedStatement(con);
        sql = statement.toString();
        dbEntry = statement.executeUpdate();
        Log.info("dbEntry: " + dbEntry);
    } catch (SQLException e) {
        Log.error("failed to insert object " + object + " into database ", e);
    } finally {

        close(null, statement, con);
        backupSQL(sql);
    }
    return dbEntry;
     }

这是我的 Gson 类代码

    public static JSONObject toJsonObject(Object o) {
    Log.info(o);
    JSONObject result = null;
    try {
        String jsonString = toJson(o);
        result = new JSONObject(jsonString);
    } catch (JSONException e) {
        Log.warning("toJSonObject failed '" + o + "'",e);
    }
    return result;
 }

我该怎么做才能避免“太多打开的连接”错误，为什么我会收到第二个错误？该类应该被初始化一次，并在整个应用程序中使用

Answer 1

第一个问题

数据库上的连接数将始终受到限制(至少受数据库服务器上 RAM 的限制)，因此:

1. 将连接数量增加到 100，如果这个数量足以满足您的测试需求，但这会消耗更多服务器资源或(更好)
2. 使用连接池来管理服务器上的连接，这是最好的解决方案，因为连接将被重用，您可以随时尝试进行测试。您可以在网上找到许多现成的解决方案。参见 here例如。

第二个问题

您的类 com.electronicarena.utils.EAGson 不在 Java 期望的位置。与 Gson 本身无关。所以你必须检查你的 PATH 变量。如果您使用的是 Eclipse，则可能是该类未编译，或者您必须检查项目首选项的“部署”部分。