java之数据库连接池-dbcp&c3p0&dbutils
介绍
因为数据库连接对象的创建比较消耗性能，所以可以在应用程序启动时就在内存中开辟一片空间（集合）存放多个数据库连接对象，后面需要连接时直接从该空间中取而不用新创建；使用完毕后归还连接（将连接重新放回空间），确保连接对象能重复使用。
知识储备
装饰者模式
package com.zze.test;
public interface IWaiter {
void service();
}
IWaiter.java
package com.zze.test;
public class Waiter implements IWaiter{
public void service(){
System.out.println("正在服务");
}
}
Waiter.java
package com.zze.test;
public class WaiterWrapper implements IWaiter {
public WaiterWrapper(Waiter waiter) {
this.waiter = waiter;
}
private Waiter waiter;
@Override
public void service() {
System.out.println("服务之前");
waiter.service();
System.out.println("服务之后");
}
}
WaiterWrapper.java
@Test
public void wrapperTest() {
IWaiter waiter = new WaiterWrapper(new Waiter());
waiter.service();
/*
服务之前
正在服务
服务之后
*/
}
test
自己实现一个连接池
通常一个连接使用完毕后我们要调用它的 close 方法关闭它，而这里我们是要让它归还到连接池，这里我们可以通过装饰者模式修改它的 close 方法实现：
package com.zze.util;
import java.sql.*;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor;
public class ConnectionWrap implements Connection {
private Connection connection = null;
private List<Connection> connectionList;
/**
* 构造函数
* @param connection 要装饰的连接
* @param connectionList 连接池储存连接的集合
*/
public ConnectionWrap(Connection connection, List<Connection> connectionList) {
super();
this.connection = connection;
this.connectionList = connectionList;
}
@Override
public void close() throws SQLException {
connectionList.add(connection);
}
@Override
public Statement createStatement() throws SQLException {
return connection.createStatement();
}
@Override
public PreparedStatement prepareStatement(String sql) throws SQLException {
return connection.prepareStatement(sql);
}
@Override
public CallableStatement prepareCall(String sql) throws SQLException {
return connection.prepareCall(sql);
}
@Override
public String nativeSQL(String sql) throws SQLException {
return connection.nativeSQL(sql);
}
@Override
public void setAutoCommit(boolean autoCommit) throws SQLException {
connection.setAutoCommit(autoCommit);
}
@Override
public boolean getAutoCommit() throws SQLException {
return connection.getAutoCommit();
}
@Override
public void commit() throws SQLException {
connection.commit();
}
@Override
public void rollback() throws SQLException {
connection.rollback();
}
@Override
public boolean isClosed() throws SQLException {
return connection.isClosed();
}
@Override
public DatabaseMetaData getMetaData() throws SQLException {
return connection.getMetaData();
}
@Override
public void setReadOnly(boolean readOnly) throws SQLException {
connection.setReadOnly(readOnly);
}
@Override
public boolean isReadOnly() throws SQLException {
return connection.isReadOnly();
}
@Override
public void setCatalog(String catalog) throws SQLException {
connection.setCatalog(catalog);
}
@Override
public String getCatalog() throws SQLException {
return connection.getCatalog();
}
@Override
public void setTransactionIsolation(int level) throws SQLException {
connection.setTransactionIsolation(level);
}
@Override
public int getTransactionIsolation() throws SQLException {
return connection.getTransactionIsolation();
}
@Override
public SQLWarning getWarnings() throws SQLException {
return connection.getWarnings();
}
@Override
public void clearWarnings() throws SQLException {
connection.clearWarnings();
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
return connection.createStatement(resultSetType, resultSetConcurrency);
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
return connection.prepareStatement(sql, resultSetType, resultSetConcurrency);
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
return connection.prepareCall(sql,resultSetType,resultSetConcurrency);
}
@Override
public Map<String, Class<?>> getTypeMap() throws SQLException {
return connection.getTypeMap();
}
@Override
public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
connection.setTypeMap(map);
}
@Override
public void setHoldability(int holdability) throws SQLException {
connection.setHoldability(holdability);
}
@Override
public int getHoldability() throws SQLException {
return connection.getHoldability();
}
@Override
public Savepoint setSavepoint() throws SQLException {
return connection.setSavepoint();
}
@Override
public Savepoint setSavepoint(String name) throws SQLException {
return connection.setSavepoint(name);
}
@Override
public void rollback(Savepoint savepoint) throws SQLException {
connection.rollback();
}
@Override
public void releaseSavepoint(Savepoint savepoint) throws SQLException {
connection.releaseSavepoint(savepoint);
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return connection.createStatement(resultSetType, resultSetConcurrency, resultSetHoldability);
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return connection.prepareStatement(sql, resultSetType, resultSetConcurrency, resultSetHoldability);
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
return connection.prepareCall(sql,resultSetType,resultSetConcurrency,resultSetHoldability);
}
@Override
public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
return connection.prepareStatement(sql, autoGeneratedKeys);
}
@Override
public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
return connection.prepareStatement(sql, columnIndexes);
}
@Override
public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
return connection.prepareStatement(sql, columnNames);
}
@Override
public Clob createClob() throws SQLException {
return connection.createClob();
}
@Override
public Blob createBlob() throws SQLException {
return connection.createBlob();
}
@Override
public NClob createNClob() throws SQLException {
return connection.createNClob();
}
@Override
public SQLXML createSQLXML() throws SQLException {
return connection.createSQLXML();
}
@Override
public boolean isValid(int timeout) throws SQLException {
return connection.isValid(timeout);
}
@Override
public void setClientInfo(String name, String value) throws SQLClientInfoException {
connection.setClientInfo(name,value);
}
@Override
public void setClientInfo(Properties properties) throws SQLClientInfoException {
connection.setClientInfo(properties);
}
@Override
public String getClientInfo(String name) throws SQLException {
return connection.getClientInfo(name);
}
@Override
public Properties getClientInfo() throws SQLException {
return connection.getClientInfo();
}
@Override
public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
return connection.createArrayOf(typeName,elements);
}
@Override
public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
return connection.createStruct(typeName,attributes);
}
@Override
public void setSchema(String schema) throws SQLException {
connection.setSchema(schema);
}
@Override
public String getSchema() throws SQLException {
return connection.getSchema();
}
@Override
public void abort(Executor executor) throws SQLException {
connection.abort(executor);
}
@Override
public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
connection.setNetworkTimeout(executor,milliseconds);
}
@Override
public int getNetworkTimeout() throws SQLException {
return connection.getNetworkTimeout();
}
@Override
public <T> T unwrap(Class<T> iface) throws SQLException {
return connection.unwrap(iface);
}
@Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
return connection.isWrapperFor(iface);
}
}
ConnectionWrap.java
对于连接池，java 已经给我们提供了接口 javax.sql.DataSource ，我们要做的就是实现它：
package com.zze.util;
import javax.sql.DataSource;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Logger;
public class MyDataSource implements DataSource {
// 定义一个集合用来存放连接
private List<Connection> connections = new ArrayList<>();
public MyDataSource() {
// 初始化 10 个连接
for (int i = 0; i < 10; i++) {
connections.add(JDBCUtil.getConnection());
}
}
/**
* 获取连接
*
* @return 从连接池取出的连接
*/
@Override
public Connection getConnection() throws SQLException {
// 取连接但集合没有连接时，新添加 5 个连接
if (connections.size() == 0) {
for (int i = 0; i < 5; i++) {
connections.add(JDBCUtil.getConnection());
}
}
Connection connection = connections.remove(0);
// 返回我们定义的连接包装类
ConnectionWrap connectionWrap = new ConnectionWrap(connection, connections);
return connectionWrap;
}
@Override
public Connection getConnection(String username, String password) throws SQLException {
return null;
}
@Override
public <T> T unwrap(Class<T> iface) throws SQLException {
return null;
}
@Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
return false;
}
@Override
public PrintWriter getLogWriter() throws SQLException {
return null;
}
@Override
public void setLogWriter(PrintWriter out) throws SQLException {
}
@Override
public void setLoginTimeout(int seconds) throws SQLException {
}
@Override
public int getLoginTimeout() throws SQLException {
return 0;
}
@Override
public Logger getParentLogger() throws SQLFeatureNotSupportedException {
return null;
}
}
MyDataSource.java
此时就可以通过我们自己编写的连接池获取连接了：
@Test
public void getConnTest() {
try {
MyDataSource dataSource = new MyDataSource();
Connection connection = dataSource.getConnection();
System.out.println(connection); // com.zze.util.ConnectionWrap@6c629d6e
} catch (SQLException e) {
e.printStackTrace();
}
}
test
第三方连接池使用
DBCP
DBCP (DataBase Connection Pool) 是 java 数据库连接池的一种，由 Apache 开发，通过它可以让程序自动管理数据库连接的释放和断开。
# 连接设置 driverClassName=com.mysql.cj.jdbc.Driver url=jdbc:mysql://localhost:3306/test username=root password=root # 初始化连接 initialSize=10 # 最大连接数量 maxActive=50 # 最大空闲连接 maxIdle=20 # 最小空闲连接 minIdle=5 # 超时等待时间以毫秒为单位 6000毫秒/1000等于60秒 maxWait=60000 # JDBC驱动建立连接时附带的连接属性属性的格式必须为这样：[属性名=property;] # 注意："user" 与 "password" 两个属性会被明确地传递，因此这里不需要包含他们。 connectionProperties=useUnicode=true;characterEncoding=gbk;serverTimezone=GMT # 指定由连接池所创建的连接的自动提交（auto-commit）状态。 defaultAutoCommit=true # driver default 指定由连接池所创建的连接的事务级别（TransactionIsolation）。 # 可用值为下列之一：（详情可见javadoc。）NONE,READ_UNCOMMITTED, READ_COMMITTED, REPEATABLE_READ, SERIALIZABLE defaultTransactionIsolation=READ_UNCOMMITTED
src:dbcpconfig.properties
package com.zze.test;
import org.apache.commons.dbcp.BasicDataSource;
import org.apache.commons.dbcp.BasicDataSourceFactory;
import org.junit.Test;
import javax.sql.DataSource;
import java.io.FileInputStream;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;
public class DemoTest {
/**
* 通过代码配置创建连接池
*/
@Test
public void dbcpTest1() {
try {
// 构建数据源对象
BasicDataSource dataSource = new BasicDataSource();
// 数据库驱动
dataSource.setDriverClassName("com.mysql.cj.jdbc.Driver");
// 用户名
dataSource.setUsername("root");
// 密码
dataSource.setPassword("root");
// 数据库链接
dataSource.setUrl("jdbc:mysql://localhost:3306/test?serverTimezone=GMT");
// 得到连接对象
Connection connection = dataSource.getConnection();
System.out.println(connection.getClass());
// class org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper
} catch (SQLException e) {
e.printStackTrace();
}
}
/**
* 通过配置文件创建连接池
*/
@Test
public void dbcpTest2() {
try {
Properties properties = new Properties();
properties.load(new FileInputStream("src//dbcpconfig.properties"));
DataSource dataSource = BasicDataSourceFactory.createDataSource(properties);
Connection connection = dataSource.getConnection();
System.out.println(connection.getClass());
} catch (Exception e) {
e.printStackTrace();
}
}
}
C3P0
C3P0 也是一个开源的 JDBC 连接池，它实现了数据源和 JNDI 绑定，支持 JDBC3 规范和 JDBC2 的标准扩展。目前使用它的开源项目有 Hibernate、Sping 等。
<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
<!--默认配置-->
<default-config>
<property name="initialPoolSize">10</property>
<property name="maxIdleTime">30</property>
<property name="maxPoolSize">100</property>
<property name="minPoolSize">10</property>
<property name="maxStatements">200</property>
</default-config>
<!--配置 mysql 连接池-->
<named-config name="mysql">
<property name="driverClass">com.mysql.jdbc.Driver</property>
<property name="jdbcUrl">jdbc:mysql://localhost:3306/test?useUnicode=true&serverTimezone=GMT&characterEncoding=utf-8</property>
<property name="user">root</property>
<property name="password">root</property>
<property name="initialPoolSize">10</property>
<property name="maxIdleTime">30</property>
<property name="maxPoolSize">100</property>
<property name="minPoolSize">10</property>
<property name="maxStatements">200</property>
</named-config>
</c3p0-config>
src:c3p0-config.xml
还可更精细的配置：
<!--acquireIncrement：链接用完了自动增量3个。 -->
<property name="acquireIncrement">3</property>
<!--acquireRetryAttempts：链接失败后重新试30次。-->
<property name="acquireRetryAttempts">30</property>
<!--acquireRetryDelay；两次连接中间隔1000毫秒。 -->
<property name="acquireRetryDelay">1000</property>
<!--autoCommitOnClose：连接关闭时默认将所有未提交的操作回滚。 -->
<property name="autoCommitOnClose">false</property>
<!--automaticTestTable：c3p0测试表，没什么用。-->
<property name="automaticTestTable">Test</property>
<!--breakAfterAcquireFailure：出错时不把正在提交的数据抛弃。-->
<property name="breakAfterAcquireFailure">false</property>
<!--checkoutTimeout：100毫秒后如果sql数据没有执行完将会报错，如果设置成0，那么将会无限的等待。 -->
<property name="checkoutTimeout">100</property>
<!--connectionTesterClassName：通过实现ConnectionTester或QueryConnectionTester的类来测试连接。类名需制定全路径。Default: com.mchange.v2.c3p0.impl.DefaultConnectionTester-->
<property name="connectionTesterClassName"></property>
<!--factoryClassLocation：指定c3p0 libraries的路径，如果（通常都是这样）在本地即可获得那么无需设置，默认null即可。-->
<property name="factoryClassLocation">null</property>
<!--forceIgnoreUnresolvedTransactions：作者强烈建议不使用的一个属性。-->
<property name="forceIgnoreUnresolvedTransactions">false</property>
<!--idleConnectionTestPeriod：每60秒检查所有连接池中的空闲连接。-->
<property name="idleConnectionTestPeriod">60</property>
<!--initialPoolSize：初始化时获取三个连接，取值应在minPoolSize与maxPoolSize之间。 -->
<property name="initialPoolSize">3</property>
<!--maxIdleTime：最大空闲时间,60秒内未使用则连接被丢弃。若为0则永不丢弃。-->
<property name="maxIdleTime">60</property>
<!--maxPoolSize：连接池中保留的最大连接数。 -->
<property name="maxPoolSize">15</property>
<!--maxStatements：最大链接数。-->
<property name="maxStatements">100</property>
<!--maxStatementsPerConnection：定义了连接池内单个连接所拥有的最大缓存statements数。Default: 0 -->
<property name="maxStatementsPerConnection"></property>
<!--numHelperThreads：异步操作，提升性能通过多线程实现多个操作同时被执行。Default: 3-->
<property name="numHelperThreads">3</property>
<!--overrideDefaultUser：当用户调用getConnection()时使root用户成为去获取连接的用户。主要用于连接池连接非c3p0的数据源时。Default: null-->
<property name="overrideDefaultUser">root</property>
<!--overrideDefaultPassword：与overrideDefaultUser参数对应使用的一个参数。Default: null-->
<property name="overrideDefaultPassword">password</property>
<!--password：密码。Default: null-->
<property name="password"></property>
<!--preferredTestQuery：定义所有连接测试都执行的测试语句。在使用连接测试的情况下这个一显著提高测试速度。注意： 测试的表必须在初始数据源的时候就存在。Default: null-->
<property name="preferredTestQuery">select id from test where id=1</property>
<!--propertyCycle：用户修改系统配置参数执行前最多等待300秒。Default: 300 -->
<property name="propertyCycle">300</property>
<!--testConnectionOnCheckout：因性能消耗大请只在需要的时候使用它。Default: false -->
<property name="testConnectionOnCheckout">false</property>
<!--testConnectionOnCheckin：如果设为true那么在取得连接的同时将校验连接的有效性。Default: false -->
<property name="testConnectionOnCheckin">true</property>
<!--user：用户名。Default: null-->
<property name="user">root</property>
<!--usesTraditionalReflectiveProxies：动态反射代理。Default: false-->
<property name="usesTraditionalReflectiveProxies">false</property>
src:c3p0-config.xml
package com.zze.test;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.junit.Test;
import javax.sql.DataSource;
import java.sql.Connection;
public class DemoTest {
/**
* 代码配置创建连接池
*/
@Test
public void c3p0Test1() {
try {
ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource();
comboPooledDataSource.setDriverClass("com.mysql.cj.jdbc.Driver");
comboPooledDataSource.setJdbcUrl("jdbc:mysql://localhost:3306/test?serverTimezone=GMT");
comboPooledDataSource.setUser("root");
comboPooledDataSource.setPassword("root");
Connection connection = comboPooledDataSource.getConnection();
System.out.println(connection);
// com.mchange.v2.c3p0.impl.NewProxyConnection@7a0ac6e3
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 配置文件创建连接池
*/
@Test
public void c3p0Test2() {
try {
//参数对应使用哪个config，如果不写，表示使用默认的config，即default-config里的配置，否则使用参数指定的named-config里的配置。
DataSource ds = new ComboPooledDataSource("mysql");
Connection connection = ds.getConnection();
System.out.println(connection);
// com.mchange.v2.c3p0.impl.NewProxyConnection@3796751b
} catch (Exception e) {
e.printStackTrace();
}
}
}
注意：配置文件名固定为 c3p0-config.xml 且需放在 src 根目录。
抽取工具类
package com.zze.util;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;
public class JDBCUtil {
private static final ComboPooledDataSource DATA_SOURCE = new ComboPooledDataSource("mysql");
private static final ThreadLocal<Connection> t = new ThreadLocal<>();
public static Connection getConnection() {
Connection conn = null;
try {
conn = t.get();
if (conn == null) {
conn = DATA_SOURCE.getConnection();
t.set(conn);
}
} catch (Exception e) {
e.printStackTrace();
}
return conn;
}
public static void beginTransaction() throws SQLException {
Connection conn = getConnection();
conn.setAutoCommit(false);
}
public static void commitTransaction() throws SQLException {
Connection conn = getConnection();
conn.commit();
}
public static DataSource getDataSource() {
return DATA_SOURCE;
}
}
DBUtils
使用
要使用 dbutils 需要提供一个连接池，这里我使用 c3p0 。
package com.zze.bean;
public class User {
public User() {
}
public User(Integer id, String username, String password) {
this.id = id;
this.username = username;
this.password = password;
}
private Integer id;
private String password;
private String username;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
@Override
public String toString() {
return String.format("id=%d,username=%s", this.id, this.username);
}
}
com.zze.bean.User
package com.zze.test;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import com.zze.bean.User;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.ResultSetHandler;
import org.junit.Test;
import javax.sql.DataSource;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
public class DemoTest {
/**
* 查询所有
*/
@Test
public void listAllTest() {
try {
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
List<User> userList = qr.query("select * from user", new ResultSetHandler<List<User>>() {
@Override
public List<User> handle(ResultSet resultSet) throws SQLException {
List<User> users = new ArrayList<>();
while (resultSet.next()) {
int id = resultSet.getInt("id");
String username = resultSet.getString("username");
String password = resultSet.getString("password");
users.add(new User(id, username, password));
}
return users;
}
});
System.out.println(userList);
// [id=1,username=张三, id=2,username=李四]
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 根据 Id 查询
*/
@Test
public void getByIdTest() {
try {
Integer id = 1;
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
User user = qr.query("select * from user where id=?", new ResultSetHandler<User>() {
@Override
public User handle(ResultSet resultSet) throws SQLException {
if (resultSet.next()) {
int id = resultSet.getInt("id");
String username = resultSet.getString("username");
String password = resultSet.getString("password");
return new User(id, username, password);
}
return null;
}
}, id);
System.out.println(user);
// id=1,username=张三
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 新增
*/
@Test
public void testAdd() {
Integer id = 1;
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
try {
int count = qr.update("insert into user (username,password) values(?,?)", "王五", "1226");
System.out.println(count > 0 ? "success" : "failed");
} catch (SQLException e) {
e.printStackTrace();
}
}
/**
* 更新
*/
@Test
public void testUpdate() {
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
try {
int count = qr.update("update user set username=? where id=?", "赵六", 3);
System.out.println(count > 0 ? "success" : "failed");
} catch (SQLException e) {
e.printStackTrace();
}
}
/**
* 删除
*/
@Test
public void testDelete() {
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
try {
int count = qr.update("delete from user where id=?", 3);
System.out.println(count > 0 ? "success" : "failed");
} catch (SQLException e) {
e.printStackTrace();
}
}
}
自己实现一个QueryRunner
package com.zze.util;
import java.sql.ResultSet;
public interface ResultHandler<T> {
T handle(ResultSet resultSet);
}
com.zze.util.ResultHandler
package com.zze.util;
import javax.sql.DataSource;
import javax.xml.crypto.Data;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class MyQueryRunner {
public MyQueryRunner(DataSource dataSource){
this.dataSource = dataSource;
}
private DataSource dataSource;
public int update(String sql, Object... args) {
try {
Connection conn = dataSource.getConnection();
PreparedStatement preparedStatement = conn.prepareStatement(sql);
int parameterCount = preparedStatement.getParameterMetaData().getParameterCount();
for (int i = 0; i < parameterCount; i++) {
preparedStatement.setObject(i + 1, args[i]);
}
return preparedStatement.executeUpdate();
} catch (Exception e) {
e.printStackTrace();
}
return 0;
}
public <T> T query(String sql, ResultHandler<T> handler, Object... args) {
try {
Connection conn = dataSource.getConnection();
PreparedStatement preparedStatement = conn.prepareStatement(sql);
int parameterCount = preparedStatement.getParameterMetaData().getParameterCount();
for (int i = 0; i < parameterCount; i++) {
preparedStatement.setObject(i + 1, args[i]);
}
ResultSet resultSet = preparedStatement.executeQuery();
T result = handler.handle(resultSet);
return result;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}
com.zze.util.MyQueryRunner
package com.zze.test;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import com.zze.bean.User;
import com.zze.util.MyQueryRunner;
import com.zze.util.ResultHandler;
import org.junit.Test;
import javax.sql.DataSource;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
/**
* 自定义的 DBUtils 测试
*/
public class MyDBUtilsTest {
/**
* 查询所有
*/
@Test
public void listAllTest() {
DataSource ds = new ComboPooledDataSource("mysql");
MyQueryRunner myQueryRunner = new MyQueryRunner(ds);
List<User> userList = myQueryRunner.query("select * from user", new ResultHandler<List<User>>() {
@Override
public List<User> handle(ResultSet resultSet) {
try {
List<User> users = new ArrayList<>();
while (resultSet.next()) {
int id = resultSet.getInt("id");
String username = resultSet.getString("username");
String password = resultSet.getString("password");
users.add(new User(id, username, password));
}
return users;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
});
System.out.println(userList);
}
@Test
public void getByIdTest() {
DataSource ds = new ComboPooledDataSource("mysql");
MyQueryRunner myQueryRunner = new MyQueryRunner(ds);
int id = 1;
User user = myQueryRunner.query("select * from user where id=?", new ResultHandler<User>() {
@Override
public User handle(ResultSet resultSet) {
try {
if (resultSet.next()) {
int id = resultSet.getInt("id");
String username = resultSet.getString("username");
String password = resultSet.getString("password");
return new User(id, username, password);
}
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
}, id);
System.out.println(user);
}
/**
* 新增
*/
@Test
public void testAdd() {
Integer id = 1;
DataSource ds = new ComboPooledDataSource("mysql");
MyQueryRunner qr = new MyQueryRunner(ds);
try {
int count = qr.update("insert into user (username,password) values(?,?)", "王五", "1226");
System.out.println(count > 0 ? "success" : "failed");
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 更新
*/
@Test
public void testUpdate() {
DataSource ds = new ComboPooledDataSource("mysql");
MyQueryRunner qr = new MyQueryRunner(ds);
try {
int count = qr.update("update user set username=? where id=?", "赵六", 7);
System.out.println(count > 0 ? "success" : "failed");
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 删除
*/
@Test
public void testDelete() {
DataSource ds = new ComboPooledDataSource("mysql");
MyQueryRunner qr = new MyQueryRunner(ds);
try {
int count = qr.update("delete from user where id=?", 6);
System.out.println(count > 0 ? "success" : "failed");
} catch (Exception e) {
e.printStackTrace();
}
}
}
DBUtils提供的结果集处理器
@Test
public void beanHandlerTest() {
try {
Integer id = 1;
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
User user = qr.query("select * from user where id=?", new BeanHandler<>(User.class), id);
System.out.println(user);
} catch (Exception e) {
e.printStackTrace();
}
}
@Test
public void beanListHandlerTest() {
try {
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
List<User> userList = qr.query("select * from user", new BeanListHandler<>(User.class));
System.out.println(userList);
} catch (Exception e) {
e.printStackTrace();
}
}
@Test
public void mapHandlerTest() {
try {
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
Map<String, Object> user = qr.query("select * from user where id=?", new MapHandler(), 2);
System.out.println(user); // {password=1226, id=2, username=李四}
} catch (Exception e) {
e.printStackTrace();
}
}
@Test
public void mapListHandlerTest() {
try {
DataSource ds = new ComboPooledDataSource("mysql");
QueryRunner qr = new QueryRunner(ds);
List<Map<String, Object>> users = qr.query("select * from user", new MapListHandler());
System.out.println(users); // [{password=1226, id=1, username=张三}, {password=1226, id=2, username=李四}]
} catch (Exception e) {
e.printStackTrace();
}
}
练习
这个练习算是对之前知识的总结，一个包含 CRUD、模糊查询、分页功能的简易版学生管理系统，点击下载。
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