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本文主要研究一下sharding-jdbc的WrapperAdapter

Wrapper

jdk-12.jdk/Contents/Home/lib/src.zip!/java.sql/java/sql/Wrapper.java

public interface Wrapper {

    <T> T unwrap(java.lang.Class<T> iface) throws java.sql.SQLException;

    boolean isWrapperFor(java.lang.Class<?> iface) throws java.sql.SQLException;

}

• Wrapper接口定义了unwrap、isWrapperFor方法

WrapperAdapter

incubator-shardingsphere-4.0.0-RC1/sharding-jdbc/sharding-jdbc-core/src/main/java/org/apache/shardingsphere/shardingjdbc/jdbc/adapter/WrapperAdapter.java

public abstract class WrapperAdapter implements Wrapper {
    
    private final Collection<JdbcMethodInvocation> jdbcMethodInvocations = new ArrayList<>();
    
    @SuppressWarnings("unchecked")
    @Override
    public final <T> T unwrap(final Class<T> iface) throws SQLException {
        if (isWrapperFor(iface)) {
            return (T) this;
        }
        throw new SQLException(String.format("[%s] cannot be unwrapped as [%s]", getClass().getName(), iface.getName()));
    }
    
    @Override
    public final boolean isWrapperFor(final Class<?> iface) {
        return iface.isInstance(this);
    }
    
    /**
     * record method invocation.
     * 
     * @param targetClass target class
     * @param methodName method name
     * @param argumentTypes argument types
     * @param arguments arguments
     */
    @SneakyThrows
    public final void recordMethodInvocation(final Class<?> targetClass, final String methodName, final Class<?>[] argumentTypes, final Object[] arguments) {
        jdbcMethodInvocations.add(new JdbcMethodInvocation(targetClass.getMethod(methodName, argumentTypes), arguments));
    }
    
    /**
     * Replay methods invocation.
     * 
     * @param target target object
     */
    public final void replayMethodsInvocation(final Object target) {
        for (JdbcMethodInvocation each : jdbcMethodInvocations) {
            each.invoke(target);
        }
    }
}

• WrapperAdapter声明实现java.sql.Wrapper接口，它定义了JdbcMethodInvocation集合；recordMethodInvocation方法会往jdbcMethodInvocations添加JdbcMethodInvocation；replayMethodsInvocation方法则会挨个执行JdbcMethodInvocation的invoke方法

JdbcMethodInvocation

incubator-shardingsphere-4.0.0-RC1/sharding-jdbc/sharding-jdbc-core/src/main/java/org/apache/shardingsphere/shardingjdbc/jdbc/adapter/invocation/JdbcMethodInvocation.java

@RequiredArgsConstructor
public class JdbcMethodInvocation {
    
    @Getter
    private final Method method;
    
    @Getter
    private final Object[] arguments;
    
    /**
     * Invoke JDBC method.
     * 
     * @param target target object
     */
    @SneakyThrows
    public void invoke(final Object target) {
        method.invoke(target, arguments);
    }
}

• JdbcMethodInvocation的invoke方法执行的是method.invoke

小结

WrapperAdapter声明实现java.sql.Wrapper接口，它定义了JdbcMethodInvocation集合；recordMethodInvocation方法会往jdbcMethodInvocations添加JdbcMethodInvocation；replayMethodsInvocation方法则会挨个执行JdbcMethodInvocation的invoke方法

doc

• WrapperAdapter