结合spring jdbc 实现分表分库的数据库访问构思

数据库的分库分表访问，原理上很简单。对于一条sql来说，就是确定表名称，对于操作来说，就是要确定数据源。因此，我要对数据源与表名进行分析。

在spring中对于单数据源的配置，非常简单，相信大家也都会配置。那么对于多数据源来说有两种方式：

1，静态数据源选择方式，只需要在dao中注入对应数据源。这种也没什么好说的，但是如果存在事物的话，需要注意，一旦在 service的方法中操作不同数据源的dao应该如何处理。

2，动态数据源选择方式。动态的方式一般会在程序中通过一定的条件来选择数据源。所以对于在spring中配置数据源就有了小小改变。目前我使用的方式是实现自己的一个数据源，这个数据源的特点就是有一个map，保存了真正需要配置的数据员，然后给每个数据源分配一个key

 

示例配置

<bean id="dataSource" class="halo.dao.sql.HaloDataSourceWrapper">
        <property name="dataSourceMap">
            <map>
                <entry key="mysql_test0">
                    <bean class="com.mchange.v2.c3p0.ComboPooledDataSource">
                        ....
                    </bean>
                </entry>
                <entry key="mysql_test1">
                    <bean class="com.mchange.v2.c3p0.ComboPooledDataSource">
                        .....
                    </bean>
                </entry>
            </map>
        </property>
    </bean>

通过这种配置方式，程序就有机会根据条件来选择相应的数据源。那么，在程序的什么位置进行数据源选择才合适呢。个人认为这属于数据访问层的职责，因此，决定数据源的选择问题交给dao来处理。对dao注入自定的数据源。然后在所有的dao的方法中，肯定会多一个参数，这个参数就为了选择数据源所使用。

示例代码

 

public int count(Object key, String where, Object[] params)

 

 

 现在选择数据源的条件有了，下面要做的就是如何根据条件选择数据源，这时，我们可以专门写一个类，来做数据源的选择以及真实表名的确定。

示例代码

 

 

/**
 * 数据库表的基本信息，包括数据库真是名称与表真是名称
 *
 * @author akwei
 */
public class PartitionTableInfo {

    /**
     * 数据源key
     */
    private String dsKey;

    /**
     * 表真是名称
     */
    private String tableName;

    /**
     * 表的别名
     */
    private String aliasName;

    public PartitionTableInfo() {
    }

    public PartitionTableInfo(String dsKey, String tableName) {
        this.dsKey = dsKey;
        this.tableName = tableName;
    }

    public String getDsKey() {
        return dsKey;
    }

    /**
     * 设置数据库真实key
     *
     * @param dsKey
     */
    public void setDsKey(String dsKey) {
        this.dsKey = dsKey;
    }

    public String getTableName() {
        return tableName;
    }

    /**
     * 设置表真实名称
     *
     * @param tableName
     */
    public void setTableName(String tableName) {
        this.tableName = tableName;
    }

    /**
     * 设置表别名
     *
     * @param aliasName
     */
    public void setAliasName(String aliasName) {
        this.aliasName = aliasName;
    }

    public String getAliasName() {
        return aliasName;
    }
}

 

 

数据源表名分析的抽象类

示例代码

 

/**
 * 数据分区分析器，通过此分析器可以分析表所在的具体的数据库与数据表名称
 *
 * @author akwei
 */
public abstract class DbPartitionHelper {

    /**
     * 根据内容进行分析，创建表的分区信息
     *
     * @param tableLogicName
     *            逻辑表名称，也将会成为表的别名
     * @param ctxMap
     *            上下文信息存储,用来存储分区关键值
     * @return
     */
    public abstract PartitionTableInfo parse(String tableLogicName,
            Map<String, Object> ctxMap);
}

 

 

数据源的选择实现类

示例代码

 

public class TestUserDbPartitionHelper extends DbPartitionHelper {

    @Override
    public PartitionTableInfo parse(String tableLogicName,
            Map<String, Object> ctxMap) {
        // 取出在程序中传递的分表分库关键字
        long userid = (Long) ctxMap.get("userid");
        // 对关键字进行分析，最终要获得真实操作的数据源key,表名称
        String lastChar = this.get01(userid);
        PartitionTableInfo partitionTableInfo = new PartitionTableInfo();
        // 设置表的逻辑表名称，也是表的别名
        partitionTableInfo.setAliasName(tableLogicName);
        // 设置通过分析后获得的真实表名称
        partitionTableInfo.setTableName("testuser" + lastChar);
        // 设置通过分析后获得的真实数据源key(此key在配置数据源时指定)
        partitionTableInfo.setDsKey("mysql_test" + lastChar);
        return partitionTableInfo;
    }
}

 

 

这样dao的方法就获得了真正的数据源key和真实的表名称

 

调用举例代码

 

// 例如：我们需要根据useri的值来作为获取数据源以及分表的条件
        TestUserDbPartitionHelper dbPartitionHelper = new TestUserDbPartitionHelper();
        Map<String, Object> ctxMap = new HashMap<String, Object>();
        ctxMap.put("userid", 123);
        PartitionTableInfo info = dbPartitionHelper.parse("testuser", ctxMap);
        String dsKey = info.getDsKey();// 数据源的key
        String realTableName = info.getTableName();// 表的真实名称

 

 通过这种调用，我么获得了数据源的key以及表的真实名称

这样dao里面的方法就可以拼装sql了。

那么数据源的key如何使用呢？

由于我们对dao都注入了自定义的datasource，这个key我们需要在datasource中通过map.get(String name)获得真实的datasource，一个简单的方式就是我们吧数据源key放到threadlocal中，让datasource在获得connection的方法中调用

 

保存数据源key的代码示例

 

/**
 * 保存当前使用的数据库key
 *
 * @author akwei
 */
public class DataSourceStatus {

    private static final ThreadLocal<String> currentDsKey = new ThreadLocal<String>();

    public static void setCurrentDsKey(String dsKey) {
        currentDsKey.set(dsKey);
    }

    public static String getCurrentDsKey() {
        return currentDsKey.get();
    }
}

 

 

自定义的datasource代码示例

 

 

/**
 * DataSource的包装类
 *
 * @author akwei
 */
public class MyDataSourceWrapper implements DataSource {

    private Map<String, DataSource> dataSourceMap;

    private PrintWriter logWriter;

    private int loginTimeout = 3;

    public DataSource getCurrentDataSource() {
        DataSource ds = this.dataSourceMap.get(DataSourceStatus
                .getCurrentDsKey());
        if (ds == null) {
            throw new RuntimeException("no datasource [ "
                    + DataSourceStatus.getCurrentDsKey() + " ]");
        }
        return ds;
    }

    public void setDataSourceMap(Map<String, DataSource> dataSourceMap) {
        this.dataSourceMap = dataSourceMap;
    }

    @Override
    public Connection getConnection() throws SQLException {
        return this.getCurrentDataSource().getConnection();
    }

    @Override
    public Connection getConnection(String username, String password)
            throws SQLException {
        throw new SQLException("only support getConnection()");
    }

    @Override
    public PrintWriter getLogWriter() throws SQLException {
        return this.logWriter;
    }

    @Override
    public int getLoginTimeout() throws SQLException {
        return this.loginTimeout;
    }

    @Override
    public void setLogWriter(PrintWriter out) throws SQLException {
        this.logWriter = out;
    }

    @Override
    public void setLoginTimeout(int seconds) throws SQLException {
        this.loginTimeout = seconds;
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return this.getCurrentDataSource().isWrapperFor(iface);
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return this.getCurrentDataSource().unwrap(iface);
    }
}

 

到目前为止，我们就可以使用spring jdbcTemplate来进行分库分表的sql操作了。

在上述的示例代码中很多的部分可以，进行数据库路由的分析写了不少的代码，其实这些代码可以通过配置的方式来解决，不需要通过手写代码来解决。我的一个思路就是对于与数据表对应的一个实体class配置一个路由规则的标示和表的别名，然后写一段程序来对这个配置进行解析，来实现上面分库分表选择的功能

上述方法解决了分库分表功能，但是没有解决单库的事务问题。由于数据库的选择是在dao层决定，那么对于一个service的方法就无法获得数据库，并开启事务。为了解决这种情况，我们可以对connection进行改造，然后再对自定义的datasource再次改造。我们在使用spring数据库事务的使用，大多情况都是在service的方法上加上事务，这样对于这个方法里面的dao调用都具有了事务操作。这样就必须在service方法运行之前就决定数据源是什么。

其实spring的事务方法只需要一个数据源，并获得connection然后进行connection.setAutoCommit等操作。spring并不关心你的connection是什么，是哪个数据源的。所以我们就可以写一个与数据源没有直接关系的自定义connection，让他来沉承担选择数据源之前对connection的所有操作。

自定义数据源示例代码

接口

 

/**
 * Connection代理,不产生实际的connection资源
 *
 * @author yuanwei
 */
public interface ConnectionProxy extends Connection {

    /**
     * 获得当前使用的Connection
     *
     * @return
     * @see Connection
     */
    Connection getCurrentConnection();
}

 

 实现

 

public class ConnectionProxyImpl implements ConnectionProxy {

    /**
     * 保存了真正的Connection
     */
    private final Map<String, Connection> conMap = new HashMap<String, Connection>();

    private boolean autoCommit;

    private int transactionIsolation;

    private int holdability;

    private boolean readOnly;

    /**
     * 自定义的数据源
     */
    private HkDataSourceWrapper cloudDataSourceWrapper;

    public ConnectionProxyImpl(HkDataSourceWrapper cloudDataSourceWrapper)
            throws SQLException {
        this.cloudDataSourceWrapper = cloudDataSourceWrapper;
        this.setAutoCommit(true);
    }

    @Override
    public void clearWarnings() throws SQLException {
        this.getCurrentConnection().clearWarnings();
    }

    @Override
    public void close() throws SQLException {
        Collection<Connection> c = this.conMap.values();
        for (Connection con : c) {
            con.close();
        }
        DataSourceStatus.setCurrentDsKey(null);
    }

    @Override
    public void commit() throws SQLException {
        Collection<Connection> c = this.conMap.values();
        for (Connection con : c) {
            con.commit();
        }
    }

    @Override
    public Statement createStatement() throws SQLException {
        return this.getCurrentConnection().createStatement();
    }

    @Override
    public Connection getCurrentConnection() {
        String name = DataSourceStatus.getCurrentDsKey();
        Connection con = this.conMap.get(name);
        if (con == null) {
            try {
                con = this.cloudDataSourceWrapper.getCurrentDataSource()
                        .getConnection();
                this.initCurrentConnection(con);
                this.conMap.put(name, con);
            }
            catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
        return con;
    }

    private void initCurrentConnection(Connection con) throws SQLException {
        con.setAutoCommit(this.getAutoCommit());
        if (this.getTransactionIsolation() != 0) {
            con.setTransactionIsolation(this.getTransactionIsolation());
        }
        con.setHoldability(this.getHoldability());
        con.setReadOnly(this.isReadOnly());
    }

    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency)
            throws SQLException {
        return this.getCurrentConnection().createStatement(resultSetType,
                resultSetConcurrency);
    }

    @Override
    public Statement createStatement(int resultSetType,
            int resultSetConcurrency, int resultSetHoldability)
            throws SQLException {
        return this.getCurrentConnection().createStatement(resultSetType,
                resultSetConcurrency, resultSetHoldability);
    }

    @Override
    public boolean getAutoCommit() throws SQLException {
        return this.autoCommit;
    }

    @Override
    public int getHoldability() throws SQLException {
        return this.holdability;
    }

    @Override
    public DatabaseMetaData getMetaData() throws SQLException {
        return this.getCurrentConnection().getMetaData();
    }

    @Override
    public int getTransactionIsolation() throws SQLException {
        return this.transactionIsolation;
    }

    @Override
    public Map<String, Class<?>> getTypeMap() throws SQLException {
        return this.getCurrentConnection().getTypeMap();
    }

    @Override
    public SQLWarning getWarnings() throws SQLException {
        return this.getCurrentConnection().getWarnings();
    }

    @Override
    public boolean isClosed() throws SQLException {
        return this.getCurrentConnection().isClosed();
    }

    @Override
    public boolean isReadOnly() throws SQLException {
        return this.readOnly;
    }

    @Override
    public String nativeSQL(String sql) throws SQLException {
        return this.getCurrentConnection().nativeSQL(sql);
    }

    @Override
    public CallableStatement prepareCall(String sql) throws SQLException {
        return this.getCurrentConnection().prepareCall(sql);
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType,
            int resultSetConcurrency) throws SQLException {
        return this.getCurrentConnection().prepareCall(sql, resultSetType,
                resultSetConcurrency);
    }

    @Override
    public CallableStatement prepareCall(String sql, int resultSetType,
            int resultSetConcurrency, int resultSetHoldability)
            throws SQLException {
        return this.getCurrentConnection().prepareCall(sql, resultSetType,
                resultSetConcurrency, resultSetHoldability);
    }

    @Override
    public PreparedStatement prepareStatement(String sql) throws SQLException {
        return this.getCurrentConnection().prepareStatement(sql);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys)
            throws SQLException {
        return this.getCurrentConnection().prepareStatement(sql,
                autoGeneratedKeys);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int[] columnIndexes)
            throws SQLException {
        return this.getCurrentConnection().prepareStatement(sql, columnIndexes);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, String[] columnNames)
            throws SQLException {
        return this.getCurrentConnection().prepareStatement(sql, columnNames);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType,
            int resultSetConcurrency) throws SQLException {
        return this.getCurrentConnection().prepareStatement(sql, resultSetType,
                resultSetConcurrency);
    }

    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType,
            int resultSetConcurrency, int resultSetHoldability)
            throws SQLException {
        return this.getCurrentConnection().prepareStatement(sql, resultSetType,
                resultSetConcurrency, resultSetHoldability);
    }

    @Override
    public void rollback() throws SQLException {
        Collection<Connection> c = conMap.values();
        for (Connection con : c) {
            con.rollback();
        }
    }

    @Override
    public void setAutoCommit(boolean autoCommit) throws SQLException {
        this.autoCommit = autoCommit;
        Collection<Connection> c = conMap.values();
        for (Connection con : c) {
            con.setAutoCommit(autoCommit);
        }
    }

    @Override
    public void setCatalog(String catalog) throws SQLException {
        this.getCurrentConnection().setCatalog(catalog);
    }

    @Override
    public String getCatalog() throws SQLException {
        return this.getCurrentConnection().getCatalog();
    }

    @Override
    public void setHoldability(int holdability) throws SQLException {
        this.holdability = holdability;
    }

    @Override
    public void setReadOnly(boolean readOnly) throws SQLException {
        this.readOnly = readOnly;
    }

    @Override
    public void setTransactionIsolation(int level) throws SQLException {
        this.transactionIsolation = level;
        Collection<Connection> c = conMap.values();
        for (Connection con : c) {
            con.setTransactionIsolation(level);
        }
    }

    @Override
    public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
        this.getCurrentConnection().setTypeMap(map);
    }

    @Override
    public void releaseSavepoint(Savepoint savepoint) throws SQLException {
        throw new SQLException("do not support savepoint");
    }

    @Override
    public void rollback(Savepoint savepoint) throws SQLException {
        throw new SQLException("do not support savepoint");
    }

    @Override
    public Savepoint setSavepoint() throws SQLException {
        throw new SQLException("do not support savepoint");
    }

    @Override
    public Savepoint setSavepoint(String name) throws SQLException {
        throw new SQLException("do not support savepoint");
    }

    @Override
    public Array createArrayOf(String typeName, Object[] elements)
            throws SQLException {
        return this.getCurrentConnection().createArrayOf(typeName, elements);
    }

    @Override
    public Blob createBlob() throws SQLException {
        return this.getCurrentConnection().createBlob();
    }

    @Override
    public Clob createClob() throws SQLException {
        return this.getCurrentConnection().createClob();
    }

    @Override
    public NClob createNClob() throws SQLException {
        return this.getCurrentConnection().createNClob();
    }

    @Override
    public SQLXML createSQLXML() throws SQLException {
        return this.getCurrentConnection().createSQLXML();
    }

    @Override
    public Struct createStruct(String typeName, Object[] attributes)
            throws SQLException {
        return this.getCurrentConnection().createStruct(typeName, attributes);
    }

    @Override
    public Properties getClientInfo() throws SQLException {
        return this.getCurrentConnection().getClientInfo();
    }

    @Override
    public String getClientInfo(String name) throws SQLException {
        Connection con = this.getCurrentConnection();
        return con.getClientInfo(name);
    }

    @Override
    public boolean isValid(int timeout) throws SQLException {
        return this.getCurrentConnection().isValid(timeout);
    }

    @Override
    public void setClientInfo(Properties properties)
            throws SQLClientInfoException {
        this.getCurrentConnection().setClientInfo(properties);
    }

    @Override
    public void setClientInfo(String name, String value)
            throws SQLClientInfoException {
        this.getCurrentConnection().setClientInfo(name, value);
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return this.getCurrentConnection().isWrapperFor(iface);
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return this.getCurrentConnection().unwrap(iface);
    }
}

 

 

然后我们对自定义的datasource再次进行改造，新的datasource代码如下

 

 

/**
 * DataSource的包装类
 *
 * @author akwei
 */
public class HkDataSourceWrapper implements DataSource, InitializingBean {

    public static final String DEFAULT_DBKEY = "defaultdbkey";

    private Map<String, DataSource> dataSourceMap;

    private PrintWriter logWriter;

    private int loginTimeout = 3;

    private boolean debugConnection;

    public void setDebugConnection(boolean debugConnection) {
        this.debugConnection = debugConnection;
    }

    public boolean isDebugConnection() {
        return debugConnection;
    }

    public DataSource getCurrentDataSource() {
        DataSource ds = this.dataSourceMap.get(DataSourceStatus
                .getCurrentDsKey());
        if (ds == null) {
            throw new RuntimeException("no datasource");
        }
        return ds;
    }

    public void setDataSourceMap(Map<String, DataSource> dataSourceMap) {
        this.dataSourceMap = dataSourceMap;
    }

    @Override
    public Connection getConnection() throws SQLException {
        return new ConnectionProxyImpl(this);
    }

    @Override
    public Connection getConnection(String username, String password)
            throws SQLException {
        throw new SQLException("only support getConnection()");
    }

    @Override
    public PrintWriter getLogWriter() throws SQLException {
        return this.logWriter;
    }

    @Override
    public int getLoginTimeout() throws SQLException {
        return this.loginTimeout;
    }

    @Override
    public void setLogWriter(PrintWriter out) throws SQLException {
        this.logWriter = out;
    }

    @Override
    public void setLoginTimeout(int seconds) throws SQLException {
        this.loginTimeout = seconds;
    }

    @Override
    public boolean isWrapperFor(Class<?> iface) throws SQLException {
        return this.getCurrentDataSource().isWrapperFor(iface);
    }

    @Override
    public <T> T unwrap(Class<T> iface) throws SQLException {
        return this.getCurrentDataSource().unwrap(iface);
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        if (this.dataSourceMap.size() == 1) {
            this.dataSourceMap.put(DEFAULT_DBKEY, this.dataSourceMap.values()
                    .iterator().next());
        }
    }
}

 

 

其中最主要的部分就是

 

@Override
    public Connection getConnection() throws SQLException {
        return new ConnectionProxyImpl(this);
    }

 

 

就是这部分返回了一个虚假的connection让spring进行事务开启等操作，那么既然spring进行了事务等设置，如何反应到真实的connection上呢，最住院哦的代码部分就是

 

private void initCurrentConnection(Connection con) throws SQLException {
        con.setAutoCommit(this.getAutoCommit());
        if (this.getTransactionIsolation() != 0) {
            con.setTransactionIsolation(this.getTransactionIsolation());
        }
        con.setHoldability(this.getHoldability());
        con.setReadOnly(this.isReadOnly());
    }

 

 

这部分代码会在获得真正的connection的时候进行对connection的初始化。这样就解决了事务问题。

评论

1 楼 antao592 2017-02-23  

楼主，HkDataSourceWrapper中的getCurrentDataSource()方法肯定会抛异常吧。开启事务的时候DataSourceStatus.getCurrentDsKey()可以还没有赋值呢